diff --git a/Cargo.toml b/Cargo.toml
index aefbca93..ffbdf0ea 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,6 +20,7 @@ libtock_low_level_debug = { path = "apis/low_level_debug" }
 libtock_platform = { path = "platform" }
 libtock_runtime = { path = "runtime" }
 libtock_temperature = { path = "apis/temperature" }
+libtock_humidity = { path = "apis/humidity" }
 
 [profile.dev]
 panic = "abort"
@@ -38,6 +39,7 @@ members = [
     "apis/gpio",
     "apis/buttons",
     "apis/console",
+    "apis/humidity",
     "apis/leds",
     "apis/low_level_debug",
     "apis/temperature",
diff --git a/apis/humidity/Cargo.toml b/apis/humidity/Cargo.toml
new file mode 100644
index 00000000..acf1ff14
--- /dev/null
+++ b/apis/humidity/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "libtock_humidity"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+libtock_platform = { path = "../../platform" }
+
+[dev-dependencies]
+libtock_unittest = { path = "../../unittest" }
\ No newline at end of file
diff --git a/apis/humidity/src/lib.rs b/apis/humidity/src/lib.rs
new file mode 100644
index 00000000..26eb1b35
--- /dev/null
+++ b/apis/humidity/src/lib.rs
@@ -0,0 +1,81 @@
+#![no_std]
+
+use core::cell::Cell;
+use libtock_platform::{
+    share, subscribe::OneId, DefaultConfig, ErrorCode, Subscribe, Syscalls, Upcall,
+};
+
+pub struct Humidity<S: Syscalls>(S);
+
+impl<S: Syscalls> Humidity<S> {
+    /// Returns Ok() if the driver was present.This does not necessarily mean
+    /// that the driver is working.
+    pub fn exists() -> Result<(), ErrorCode> {
+        S::command(DRIVER_NUM, EXISTS, 0, 0).to_result()
+    }
+
+    /// Initiate a humidity measurement.
+    ///
+    /// This function is used both for synchronous and asynchronous readings
+    pub fn read_humidity() -> Result<(), ErrorCode> {
+        S::command(DRIVER_NUM, READ_HUM, 0, 0).to_result()
+    }
+
+    /// Register an events listener
+    pub fn register_listener<'share, F: Fn(i32)>(
+        listener: &'share HumidityListener<F>,
+        subscribe: share::Handle<Subscribe<'share, S, DRIVER_NUM, 0>>,
+    ) -> Result<(), ErrorCode> {
+        S::subscribe::<_, _, DefaultConfig, DRIVER_NUM, 0>(subscribe, listener)
+    }
+
+    /// Unregister the events listener
+    pub fn unregister_listener() {
+        S::unsubscribe(DRIVER_NUM, 0)
+    }
+
+    /// Initiate a synchronous humidity measurement.
+    /// Returns Ok(humidity_value) if the operation was successful
+    /// humidity_value is returned in hundreds of centigrades
+    pub fn read_humidity_sync() -> Result<i32, ErrorCode> {
+        let humidity_cell: Cell<Option<i32>> = Cell::new(None);
+        let listener = HumidityListener(|hum_val| {
+            humidity_cell.set(Some(hum_val));
+        });
+        share::scope(|subscribe| {
+            if let Ok(()) = Self::register_listener(&listener, subscribe) {
+                if let Ok(()) = Self::read_humidity() {
+                    while humidity_cell.get() == None {
+                        S::yield_wait();
+                    }
+                }
+            }
+        });
+
+        match humidity_cell.get() {
+            None => Err(ErrorCode::Busy),
+            Some(hum_val) => Ok(hum_val),
+        }
+    }
+}
+
+pub struct HumidityListener<F: Fn(i32)>(pub F);
+impl<F: Fn(i32)> Upcall<OneId<DRIVER_NUM, 0>> for HumidityListener<F> {
+    fn upcall(&self, hum_val: u32, _arg1: u32, _arg2: u32) {
+        self.0(hum_val as i32)
+    }
+}
+
+#[cfg(test)]
+mod tests;
+
+// -----------------------------------------------------------------------------
+// Driver number and command IDs
+// -----------------------------------------------------------------------------
+
+const DRIVER_NUM: u32 = 0x60001;
+
+// Command IDs
+
+const EXISTS: u32 = 0;
+const READ_HUM: u32 = 1;
diff --git a/apis/humidity/src/tests.rs b/apis/humidity/src/tests.rs
new file mode 100644
index 00000000..f7af706e
--- /dev/null
+++ b/apis/humidity/src/tests.rs
@@ -0,0 +1,81 @@
+use core::cell::Cell;
+use libtock_platform::{share, ErrorCode, Syscalls, YieldNoWaitReturn};
+use libtock_unittest::fake;
+
+type Humidity = super::Humidity<fake::Syscalls>;
+
+#[test]
+fn no_driver() {
+    let _kernel = fake::Kernel::new();
+    assert_eq!(Humidity::exists(), Err(ErrorCode::NoDevice));
+}
+
+#[test]
+fn driver_check() {
+    let kernel = fake::Kernel::new();
+    let driver = fake::Humidity::new();
+    kernel.add_driver(&driver);
+
+    assert_eq!(Humidity::exists(), Ok(()));
+}
+
+#[test]
+fn read_humidity() {
+    let kernel = fake::Kernel::new();
+    let driver = fake::Humidity::new();
+    kernel.add_driver(&driver);
+
+    assert_eq!(Humidity::read_humidity(), Ok(()));
+    assert!(driver.is_busy());
+
+    assert_eq!(Humidity::read_humidity(), Err(ErrorCode::Busy));
+    assert_eq!(Humidity::read_humidity_sync(), Err(ErrorCode::Busy));
+}
+
+#[test]
+fn register_unregister_listener() {
+    let kernel = fake::Kernel::new();
+    let driver = fake::Humidity::new();
+    kernel.add_driver(&driver);
+
+    let humidity_cell: Cell<Option<i32>> = Cell::new(None);
+    let listener = crate::HumidityListener(|hum_val| {
+        humidity_cell.set(Some(hum_val));
+    });
+    share::scope(|subscribe| {
+        assert_eq!(Humidity::read_humidity(), Ok(()));
+        driver.set_value(100);
+        assert_eq!(fake::Syscalls::yield_no_wait(), YieldNoWaitReturn::NoUpcall);
+
+        assert_eq!(Humidity::register_listener(&listener, subscribe), Ok(()));
+        assert_eq!(Humidity::read_humidity(), Ok(()));
+        driver.set_value(100);
+        assert_eq!(fake::Syscalls::yield_no_wait(), YieldNoWaitReturn::Upcall);
+        assert_eq!(humidity_cell.get(), Some(100));
+
+        Humidity::unregister_listener();
+        assert_eq!(Humidity::read_humidity(), Ok(()));
+        driver.set_value(100);
+        assert_eq!(fake::Syscalls::yield_no_wait(), YieldNoWaitReturn::NoUpcall);
+    });
+}
+
+#[test]
+fn read_humidity_sync() {
+    let kernel = fake::Kernel::new();
+    let driver = fake::Humidity::new();
+    kernel.add_driver(&driver);
+
+    driver.set_value_sync(1000);
+    assert_eq!(Humidity::read_humidity_sync(), Ok(1000));
+}
+
+#[test]
+fn negative_value() {
+    let kernel = fake::Kernel::new();
+    let driver = fake::Humidity::new();
+    kernel.add_driver(&driver);
+
+    driver.set_value_sync(-1000);
+    assert_eq!(Humidity::read_humidity_sync(), Ok(-1000));
+}
diff --git a/examples/humidity.rs b/examples/humidity.rs
new file mode 100644
index 00000000..138997a3
--- /dev/null
+++ b/examples/humidity.rs
@@ -0,0 +1,41 @@
+//! A simple libtock-rs example. Checks for humidity driver
+//! and samples the sensor every 2 seconds.
+
+#![no_main]
+#![no_std]
+
+use core::fmt::Write;
+use libtock::console::Console;
+
+use libtock::alarm::{Alarm, Milliseconds};
+use libtock::humidity::Humidity;
+use libtock::runtime::{set_main, stack_size};
+
+set_main! {main}
+stack_size! {0x200}
+
+fn main() {
+    match Humidity::exists() {
+        Ok(()) => writeln!(Console::writer(), "humidity driver available").unwrap(),
+        Err(_) => {
+            writeln!(Console::writer(), "humidity driver unavailable").unwrap();
+            return;
+        }
+    }
+
+    loop {
+        match Humidity::read_humidity_sync() {
+            Ok(hum_val) => writeln!(
+                Console::writer(),
+                "Humidity: {}{}.{}*C\n",
+                if hum_val > 0 { "" } else { "-" },
+                i32::abs(hum_val) / 100,
+                i32::abs(hum_val) % 100
+            )
+            .unwrap(),
+            Err(_) => writeln!(Console::writer(), "error while reading humidity",).unwrap(),
+        }
+
+        Alarm::sleep_for(Milliseconds(2000)).unwrap();
+    }
+}
diff --git a/log.log b/log.log
new file mode 100644
index 00000000..8de839cb
--- /dev/null
+++ b/log.log
@@ -0,0 +1,969 @@
+    Finished release [optimized + debuginfo] target(s) in 0.03s
+    Finished release [optimized + debuginfo] target(s) in 0.02s
+    Finished dev [unoptimized + debuginfo] target(s) in 0.05s
+    Checking libtock_platform v0.1.0 (/home/alex/myfork/libtock-rs/platform)
+   Compiling libtock_runtime v0.1.0 (/home/alex/myfork/libtock-rs/runtime)
+    Checking ufmt-write v0.1.0 (/home/alex/myfork/libtock-rs/ufmt/write)
+error[E0463]: can't find crate for `core`
+  |
+  = note: the `thumbv7em-none-eabi` target may not be installed
+  = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `compiler_builtins`
+
+error[E0412]: cannot find type `Result` in this scope
+  --> ufmt/write/src/lib.rs:22:41
+   |
+22 |     fn write_str(&mut self, s: &str) -> Result<(), Self::Error>;
+   |                                         ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+  --> ufmt/write/src/lib.rs:29:42
+   |
+29 |     fn write_char(&mut self, c: char) -> Result<(), Self::Error> {
+   |                                          ^^^^^^ not found in this scope
+
+error: requires `receiver` lang_item
+  --> ufmt/write/src/lib.rs:22:18
+   |
+22 |     fn write_str(&mut self, s: &str) -> Result<(), Self::Error>;
+   |                  ^^^^^^^^^
+
+error: requires `receiver` lang_item
+  --> ufmt/write/src/lib.rs:29:19
+   |
+29 |     fn write_char(&mut self, c: char) -> Result<(), Self::Error> {
+   |                   ^^^^^^^^^
+
+Some errors have detailed explanations: E0412, E0463.
+For more information about an error, try `rustc --explain E0412`.
+error: could not compile `ufmt-write` due to 6 previous errors
+warning: build failed, waiting for other jobs to finish...
+error[E0463]: can't find crate for `core`
+ --> platform/src/allow_ro.rs:3:5
+  |
+3 | use core::marker::PhantomData;
+  |     ^^^^ can't find crate
+  |
+  = note: the `thumbv7em-none-eabi` target may not be installed
+  = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+ --> platform/src/allow_rw.rs:3:5
+  |
+3 | use core::marker::PhantomData;
+  |     ^^^^ can't find crate
+  |
+  = note: the `thumbv7em-none-eabi` target may not be installed
+  = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+ --> platform/src/share/handle.rs:2:5
+  |
+2 | use core::marker::PhantomData;
+  |     ^^^^ can't find crate
+  |
+  = note: the `thumbv7em-none-eabi` target may not be installed
+  = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+ --> platform/src/command_return.rs:3:5
+  |
+3 | use core::mem::transmute;
+  |     ^^^^ can't find crate
+  |
+  = note: the `thumbv7em-none-eabi` target may not be installed
+  = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+ --> platform/src/error_code.rs:1:5
+  |
+1 | use core::{convert::TryFrom, fmt, mem::transmute};
+  |     ^^^^ can't find crate
+  |
+  = note: the `thumbv7em-none-eabi` target may not be installed
+  = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error: cannot find attribute `derive` in this scope
+  --> platform/src/command_return.rs:62:3
+   |
+62 | #[derive(Clone, Copy, Debug)]
+   |   ^^^^^^
+
+error: cannot find attribute `derive` in this scope
+ --> platform/src/error_code.rs:9:3
+  |
+9 | #[derive(Clone, Copy, PartialEq, Eq)]
+  |   ^^^^^^
+
+error: cannot find attribute `derive` in this scope
+   --> platform/src/error_code.rs:240:3
+    |
+240 | #[derive(PartialEq, Eq, Debug)]
+    |   ^^^^^^
+
+error: cannot find macro `write` in this scope
+   --> platform/src/error_code.rs:269:24
+    |
+269 |             Some(s) => write!(f, "{}", s),
+    |                        ^^^^^
+
+error: cannot find macro `write` in this scope
+   --> platform/src/error_code.rs:270:21
+    |
+270 |             None => write!(f, "code {}", *self as u16),
+    |                     ^^^^^
+
+error: cannot find attribute `derive` in this scope
+ --> platform/src/register.rs:9:3
+  |
+9 | #[derive(Clone, Copy, Debug)]
+  |   ^^^^^^
+
+error: cannot find attribute `derive` in this scope
+ --> platform/src/return_variant.rs:8:3
+  |
+8 | #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+  |   ^^^^^^
+
+error: cannot find attribute `derive` in this scope
+  --> platform/src/yield_types.rs:10:3
+   |
+10 | #[derive(Clone, Copy, Debug, Eq, PartialEq)]
+   |   ^^^^^^
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/allow_ro.rs:31:25
+   |
+31 |     _share: PhantomData<core::cell::Cell<&'share [u8]>>,
+   |                         ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/allow_rw.rs:31:25
+   |
+31 |     _share: PhantomData<core::cell::Cell<&'share mut [u8]>>,
+   |                         ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/exit_on_drop.rs:15:43
+   |
+15 | pub struct ExitOnDrop<S: crate::Syscalls>(core::marker::PhantomData<S>);
+   |                                           ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/exit_on_drop.rs:19:20
+   |
+19 |         ExitOnDrop(core::marker::PhantomData)
+   |                    ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/register.rs:92:18
+   |
+92 |     type Error = core::num::TryFromIntError;
+   |                  ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/register.rs:94:52
+   |
+94 |     fn try_from(register: Register) -> Result<u32, core::num::TryFromIntError> {
+   |                                                    ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/subscribe.rs:13:16
+   |
+13 |     _syscalls: core::marker::PhantomData<S>,
+   |                ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/subscribe.rs:25:13
+   |
+25 |     _scope: core::marker::PhantomData<core::cell::Cell<&'share ()>>,
+   |             ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/subscribe.rs:25:39
+   |
+25 |     _scope: core::marker::PhantomData<core::cell::Cell<&'share ()>>,
+   |                                       ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/subscribe.rs:90:24
+   |
+90 | impl Upcall<AnyId> for core::cell::Cell<bool> {
+   |                        ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/subscribe.rs:99:24
+   |
+99 | impl Upcall<AnyId> for core::cell::Cell<Option<()>> {
+   |                        ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+   --> platform/src/subscribe.rs:106:24
+    |
+106 | impl Upcall<AnyId> for core::cell::Cell<Option<(u32,)>> {
+    |                        ^^^^ can't find crate
+    |
+    = note: the `thumbv7em-none-eabi` target may not be installed
+    = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+   --> platform/src/subscribe.rs:113:24
+    |
+113 | impl Upcall<AnyId> for core::cell::Cell<Option<(u32, u32)>> {
+    |                        ^^^^ can't find crate
+    |
+    = note: the `thumbv7em-none-eabi` target may not be installed
+    = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+   --> platform/src/subscribe.rs:120:24
+    |
+120 | impl Upcall<AnyId> for core::cell::Cell<Option<(u32, u32, u32)>> {
+    |                        ^^^^ can't find crate
+    |
+    = note: the `thumbv7em-none-eabi` target may not be installed
+    = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/syscalls_impl.rs:15:24
+   |
+15 |         let mut flag = core::mem::MaybeUninit::<YieldNoWaitReturn>::uninit();
+   |                        ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+  --> platform/src/syscalls_impl.rs:65:13
+   |
+65 |             core::mem::forget(exit);
+   |             ^^^^ can't find crate
+   |
+   = note: the `thumbv7em-none-eabi` target may not be installed
+   = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+   --> platform/src/syscalls_impl.rs:121:37
+    |
+121 |                 return Err(unsafe { core::mem::transmute(r1.as_u32()) });
+    |                                     ^^^^ can't find crate
+    |
+    = note: the `thumbv7em-none-eabi` target may not be installed
+    = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+   --> platform/src/syscalls_impl.rs:234:37
+    |
+234 |                 return Err(unsafe { core::mem::transmute(r1.as_u32()) });
+    |                                     ^^^^ can't find crate
+    |
+    = note: the `thumbv7em-none-eabi` target may not be installed
+    = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+   --> platform/src/syscalls_impl.rs:321:37
+    |
+321 |                 return Err(unsafe { core::mem::transmute(r1.as_u32()) });
+    |                                     ^^^^ can't find crate
+    |
+    = note: the `thumbv7em-none-eabi` target may not be installed
+    = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+   --> platform/src/syscalls_impl.rs:370:13
+    |
+370 |             core::hint::unreachable_unchecked()
+    |             ^^^^ can't find crate
+    |
+    = note: the `thumbv7em-none-eabi` target may not be installed
+    = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0463]: can't find crate for `core`
+   --> platform/src/syscalls_impl.rs:382:13
+    |
+382 |             core::hint::unreachable_unchecked()
+    |             ^^^^ can't find crate
+    |
+    = note: the `thumbv7em-none-eabi` target may not be installed
+    = help: consider downloading the target with `rustup target add thumbv7em-none-eabi`
+
+error[E0405]: cannot find trait `Default` in this scope
+  --> platform/src/allow_ro.rs:37:73
+   |
+37 | impl<'share, S: Syscalls, const DRIVER_NUM: u32, const BUFFER_NUM: u32> Default
+   |                                                                         ^^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Drop` in this scope
+  --> platform/src/allow_ro.rs:48:73
+   |
+48 | impl<'share, S: Syscalls, const DRIVER_NUM: u32, const BUFFER_NUM: u32> Drop
+   |                                                                         ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Default` in this scope
+  --> platform/src/allow_rw.rs:37:73
+   |
+37 | impl<'share, S: Syscalls, const DRIVER_NUM: u32, const BUFFER_NUM: u32> Default
+   |                                                                         ^^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Drop` in this scope
+  --> platform/src/allow_rw.rs:48:73
+   |
+48 | impl<'share, S: Syscalls, const DRIVER_NUM: u32, const BUFFER_NUM: u32> Drop
+   |                                                                         ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:138:34
+    |
+138 |     pub fn get_failure(&self) -> Option<ErrorCode> {
+    |                                  ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:140:20
+    |
+140 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:147:38
+    |
+147 |     pub fn get_failure_u32(&self) -> Option<(ErrorCode, u32)> {
+    |                                      ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:149:20
+    |
+149 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:156:40
+    |
+156 |     pub fn get_failure_2_u32(&self) -> Option<(ErrorCode, u32, u32)> {
+    |                                        ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:158:20
+    |
+158 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:165:38
+    |
+165 |     pub fn get_failure_u64(&self) -> Option<(ErrorCode, u64)> {
+    |                                      ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:167:20
+    |
+167 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:176:38
+    |
+176 |     pub fn get_success_u32(&self) -> Option<u32> {
+    |                                      ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:178:20
+    |
+178 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:184:40
+    |
+184 |     pub fn get_success_2_u32(&self) -> Option<(u32, u32)> {
+    |                                        ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:186:20
+    |
+186 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:192:38
+    |
+192 |     pub fn get_success_u64(&self) -> Option<u64> {
+    |                                      ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:194:20
+    |
+194 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:200:40
+    |
+200 |     pub fn get_success_3_u32(&self) -> Option<(u32, u32, u32)> {
+    |                                        ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:202:20
+    |
+202 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/command_return.rs:209:42
+    |
+209 |     pub fn get_success_u32_u64(&self) -> Option<(u32, u64)> {
+    |                                          ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/command_return.rs:211:20
+    |
+211 |             return None;
+    |                    ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+   --> platform/src/command_return.rs:235:37
+    |
+235 |     pub fn to_result<T, E>(self) -> Result<T, E>
+    |                                     ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/error_code.rs:245:24
+    |
+245 |     fn as_str(self) -> Option<&'static str> {
+    |                        ^^^^^^ not found in this scope
+
+error[E0425]: cannot find value `None` in this scope
+   --> platform/src/error_code.rs:261:18
+    |
+261 |             _ => None,
+    |                  ^^^^ not found in this scope
+
+error[E0531]: cannot find tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:269:13
+    |
+269 |             Some(s) => write!(f, "{}", s),
+    |             ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+   --> platform/src/error_code.rs:278:32
+    |
+278 |     fn try_from(value: u32) -> Result<Self, Self::Error> {
+    |                                ^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Default` in this scope
+  --> platform/src/exit_on_drop.rs:17:26
+   |
+17 | impl<S: crate::Syscalls> Default for ExitOnDrop<S> {
+   |                          ^^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Drop` in this scope
+  --> platform/src/exit_on_drop.rs:23:26
+   |
+23 | impl<S: crate::Syscalls> Drop for ExitOnDrop<S> {
+   |                          ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Sized` in this scope
+  --> platform/src/raw_syscalls.rs:66:31
+   |
+66 | pub unsafe trait RawSyscalls: Sized {
+   |                               ^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/register.rs:17:6
+   |
+17 | impl From<crate::ErrorCode> for Register {
+   |      ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/register.rs:23:6
+   |
+23 | impl From<u32> for Register {
+   |      ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/register.rs:29:6
+   |
+29 | impl From<usize> for Register {
+   |      ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/register.rs:35:9
+   |
+35 | impl<T> From<*mut T> for Register {
+   |         ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/register.rs:41:9
+   |
+41 | impl<T> From<*const T> for Register {
+   |         ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/register.rs:66:6
+   |
+66 | impl From<Register> for usize {
+   |      ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/register.rs:72:9
+   |
+72 | impl<T> From<Register> for *mut T {
+   |         ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/register.rs:78:9
+   |
+78 | impl<T> From<Register> for *const T {
+   |         ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `TryFrom` in this scope
+  --> platform/src/register.rs:91:6
+   |
+91 | impl TryFrom<Register> for u32 {
+   |      ^^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+  --> platform/src/register.rs:94:40
+   |
+94 |     fn try_from(register: Register) -> Result<u32, core::num::TryFromIntError> {
+   |                                        ^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/return_variant.rs:11:6
+   |
+11 | impl From<u32> for ReturnVariant {
+   |      ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/return_variant.rs:17:6
+   |
+17 | impl From<ReturnVariant> for crate::Register {
+   |      ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `From` in this scope
+  --> platform/src/return_variant.rs:23:6
+   |
+23 | impl From<ReturnVariant> for u32 {
+   |      ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Clone` in this scope
+  --> platform/src/share/handle.rs:25:24
+   |
+25 | impl<'handle, L: List> Clone for Handle<'handle, L> {
+   |                        ^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Copy` in this scope
+  --> platform/src/share/handle.rs:31:24
+   |
+31 | impl<'handle, L: List> Copy for Handle<'handle, L> {}
+   |                        ^^^^ not found in this scope
+
+error[E0405]: cannot find trait `FnOnce` in this scope
+  --> platform/src/share/mod.rs:10:34
+   |
+10 | pub fn scope<L: List, Output, F: FnOnce(Handle<L>) -> Output>(fcn: F) -> Output {
+   |                                  ^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Default` in this scope
+  --> platform/src/share/mod.rs:21:17
+   |
+21 | pub trait List: Default {}
+   |                 ^^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Default` in this scope
+  --> platform/src/subscribe.rs:31:76
+   |
+31 | impl<'share, S: Syscalls, const DRIVER_NUM: u32, const SUBSCRIBE_NUM: u32> Default
+   |                                                                            ^^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Drop` in this scope
+  --> platform/src/subscribe.rs:42:76
+   |
+42 | impl<'share, S: Syscalls, const DRIVER_NUM: u32, const SUBSCRIBE_NUM: u32> Drop
+   |                                                                            ^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+  --> platform/src/subscribe.rs:99:41
+   |
+99 | impl Upcall<AnyId> for core::cell::Cell<Option<()>> {
+   |                                         ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/subscribe.rs:106:41
+    |
+106 | impl Upcall<AnyId> for core::cell::Cell<Option<(u32,)>> {
+    |                                         ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/subscribe.rs:113:41
+    |
+113 | impl Upcall<AnyId> for core::cell::Cell<Option<(u32, u32)>> {
+    |                                         ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Option` in this scope
+   --> platform/src/subscribe.rs:120:41
+    |
+120 | impl Upcall<AnyId> for core::cell::Cell<Option<(u32, u32, u32)>> {
+    |                                         ^^^^^^ not found in this scope
+
+error[E0405]: cannot find trait `Sized` in this scope
+ --> platform/src/syscalls.rs:9:35
+  |
+9 | pub trait Syscalls: RawSyscalls + Sized {
+  |                                   ^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+  --> platform/src/syscalls.rs:38:10
+   |
+38 |     ) -> Result<(), ErrorCode>;
+   |          ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+  --> platform/src/syscalls.rs:58:10
+   |
+58 |     ) -> Result<(), ErrorCode>;
+   |          ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+  --> platform/src/syscalls.rs:73:10
+   |
+73 |     ) -> Result<(), ErrorCode>;
+   |          ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+  --> platform/src/syscalls_impl.rs:52:10
+   |
+52 |     ) -> Result<(), ErrorCode> {
+   |          ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+  --> platform/src/syscalls_impl.rs:81:14
+   |
+81 |         ) -> Result<(), ErrorCode> {
+   |              ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+   --> platform/src/syscalls_impl.rs:191:10
+    |
+191 |     ) -> Result<(), ErrorCode> {
+    |          ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+   --> platform/src/syscalls_impl.rs:201:14
+    |
+201 |         ) -> Result<(), ErrorCode> {
+    |              ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+   --> platform/src/syscalls_impl.rs:275:10
+    |
+275 |     ) -> Result<(), ErrorCode> {
+    |          ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+   --> platform/src/syscalls_impl.rs:288:14
+    |
+288 |         ) -> Result<(), ErrorCode> {
+    |              ^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Result` in this scope
+  --> platform/src/termination.rs:16:22
+   |
+16 | impl Termination for Result<(), ErrorCode> {
+   |                      ^^^^^^ not found in this scope
+
+error[E0531]: cannot find tuple struct or tuple variant `Ok` in this scope
+  --> platform/src/termination.rs:19:13
+   |
+19 |             Ok(()) => 0,
+   |             ^^ not found in this scope
+
+error[E0531]: cannot find tuple struct or tuple variant `Err` in this scope
+  --> platform/src/termination.rs:20:13
+   |
+20 |             Err(ec) => ec as u32,
+   |             ^^^ not found in this scope
+
+error[E0433]: failed to resolve: use of undeclared type `Default`
+  --> platform/src/share/mod.rs:11:16
+   |
+11 |     let list = Default::default();
+   |                ^^^^^^^ use of undeclared type `Default`
+
+error[E0433]: failed to resolve: use of undeclared type `Default`
+  --> platform/src/subscribe.rs:36:24
+   |
+36 |             _syscalls: Default::default(),
+   |                        ^^^^^^^ use of undeclared type `Default`
+
+error[E0433]: failed to resolve: use of undeclared type `Default`
+  --> platform/src/subscribe.rs:37:21
+   |
+37 |             _scope: Default::default(),
+   |                     ^^^^^^^ use of undeclared type `Default`
+
+error[E0433]: failed to resolve: use of undeclared type `Default`
+  --> platform/src/syscalls_impl.rs:62:53
+   |
+62 |             let exit: exit_on_drop::ExitOnDrop<S> = Default::default();
+   |                                                     ^^^^^^^ use of undeclared type `Default`
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:142:9
+    |
+142 |         Some(unsafe { transmute(self.r1) })
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:151:9
+    |
+151 |         Some((unsafe { transmute(self.r1) }, self.r2))
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:160:9
+    |
+160 |         Some((unsafe { transmute(self.r1) }, self.r2, self.r3))
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:169:9
+    |
+169 |         Some((
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:180:9
+    |
+180 |         Some(self.r1)
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:188:9
+    |
+188 |         Some((self.r1, self.r2))
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:196:9
+    |
+196 |         Some(self.r1 as u64 + ((self.r2 as u64) << 32))
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:204:9
+    |
+204 |         Some((self.r1, self.r2, self.r3))
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/command_return.rs:213:9
+    |
+213 |         Some((self.r1, self.r2 as u64 + ((self.r3 as u64) << 32)))
+    |         ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Ok` in this scope
+   --> platform/src/command_return.rs:242:20
+    |
+242 |             return Ok(T::from_raw_values(r1, r2, r3));
+    |                    ^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Err` in this scope
+   --> platform/src/command_return.rs:253:9
+    |
+253 |         Err(E::from_raw_values(ec, r2, r3))
+    |         ^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:247:27
+    |
+247 |             Self::Fail => Some("FAIL"),
+    |                           ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:248:27
+    |
+248 |             Self::Busy => Some("BUSY"),
+    |                           ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:249:30
+    |
+249 |             Self::Already => Some("ALREADY"),
+    |                              ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:250:26
+    |
+250 |             Self::Off => Some("OFF"),
+    |                          ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:251:30
+    |
+251 |             Self::Reserve => Some("RESERVE"),
+    |                              ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:252:30
+    |
+252 |             Self::Invalid => Some("INVALID"),
+    |                              ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:253:27
+    |
+253 |             Self::Size => Some("SIZE"),
+    |                           ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:254:29
+    |
+254 |             Self::Cancel => Some("CANCEL"),
+    |                             ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:255:28
+    |
+255 |             Self::NoMem => Some("NOMEM"),
+    |                            ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:256:32
+    |
+256 |             Self::NoSupport => Some("NOSUPPORT"),
+    |                                ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:257:31
+    |
+257 |             Self::NoDevice => Some("NODEVICE"),
+    |                               ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:258:34
+    |
+258 |             Self::Uninstalled => Some("UNINSTALLED"),
+    |                                  ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:259:28
+    |
+259 |             Self::NoAck => Some("NOACK"),
+    |                            ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/error_code.rs:260:30
+    |
+260 |             Self::BadRVal => Some("BADRVAL"),
+    |                              ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Ok` in this scope
+   --> platform/src/error_code.rs:280:13
+    |
+280 |             Ok(unsafe { transmute(value) })
+    |             ^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Err` in this scope
+   --> platform/src/error_code.rs:282:13
+    |
+282 |             Err(NotAnErrorCode)
+    |             ^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/subscribe.rs:101:18
+    |
+101 |         self.set(Some(()));
+    |                  ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/subscribe.rs:108:18
+    |
+108 |         self.set(Some((arg0,)));
+    |                  ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/subscribe.rs:115:18
+    |
+115 |         self.set(Some((arg0, arg1)));
+    |                  ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Some` in this scope
+   --> platform/src/subscribe.rs:122:18
+    |
+122 |         self.set(Some((arg0, arg1, arg2)));
+    |                  ^^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Err` in this scope
+   --> platform/src/syscalls_impl.rs:121:24
+    |
+121 |                 return Err(unsafe { core::mem::transmute(r1.as_u32()) });
+    |                        ^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Ok` in this scope
+   --> platform/src/syscalls_impl.rs:134:13
+    |
+134 |             Ok(())
+    |             ^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Err` in this scope
+   --> platform/src/syscalls_impl.rs:234:24
+    |
+234 |                 return Err(unsafe { core::mem::transmute(r1.as_u32()) });
+    |                        ^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Ok` in this scope
+   --> platform/src/syscalls_impl.rs:245:13
+    |
+245 |             Ok(())
+    |             ^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Err` in this scope
+   --> platform/src/syscalls_impl.rs:321:24
+    |
+321 |                 return Err(unsafe { core::mem::transmute(r1.as_u32()) });
+    |                        ^^^ not found in this scope
+
+error[E0425]: cannot find function, tuple struct or tuple variant `Ok` in this scope
+   --> platform/src/syscalls_impl.rs:332:13
+    |
+332 |             Ok(())
+    |             ^^ not found in this scope
+
+Some errors have detailed explanations: E0405, E0412, E0425, E0433, E0463, E0531.
+For more information about an error, try `rustc --explain E0405`.
+error: could not compile `libtock_platform` due to 143 previous errors
+make: *** [Makefile:112: test-stable] Error 101
diff --git a/src/lib.rs b/src/lib.rs
index c13b39db..e0745aea 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -29,6 +29,12 @@ pub mod gpio {
         PullDown, PullNone, PullUp,
     };
 }
+
+pub mod humidity {
+    use libtock_humidity as humidity;
+    pub type Humidity = humidity::Humidity<super::runtime::TockSyscalls>;
+}
+
 pub mod leds {
     use libtock_leds as leds;
     pub type Leds = leds::Leds<super::runtime::TockSyscalls>;
diff --git a/unittest/src/fake/humidity/mod.rs b/unittest/src/fake/humidity/mod.rs
new file mode 100644
index 00000000..d5110935
--- /dev/null
+++ b/unittest/src/fake/humidity/mod.rs
@@ -0,0 +1,85 @@
+//! Fake implementation of the Humidity API, documented here:
+//! https://github.com/tock/tock/blob/master/doc/syscalls/60000_ambient_humidity.md
+//!
+//! Like the real API, `Humidity` controls a fake humidity sensor. It provides
+//! a function `set_value` used to immediately call an upcall with a humidity value read by the sensor
+//! and a function 'set_value_sync' used to call the upcall when the read command is received.
+
+use crate::{DriverInfo, DriverShareRef};
+use libtock_platform::{CommandReturn, ErrorCode};
+use std::cell::Cell;
+
+// The `upcall_on_command` field is set to Some(value) if an upcall(with value as its argument) should be called when read command is received,
+// or None otherwise. It was needed for testing `read_sync` library function which simulates a synchronous humidity read,
+// because it was impossible to schedule an upcall during the `synchronous` read in other ways.
+pub struct Humidity {
+    busy: Cell<bool>,
+    upcall_on_command: Cell<Option<i32>>,
+    share_ref: DriverShareRef,
+}
+
+impl Humidity {
+    pub fn new() -> std::rc::Rc<Humidity> {
+        std::rc::Rc::new(Humidity {
+            busy: Cell::new(false),
+            upcall_on_command: Cell::new(None),
+            share_ref: Default::default(),
+        })
+    }
+
+    pub fn is_busy(&self) -> bool {
+        self.busy.get()
+    }
+    pub fn set_value(&self, value: i32) {
+        if self.busy.get() {
+            self.share_ref
+                .schedule_upcall(0, (value as u32, 0, 0))
+                .expect("Unable to schedule upcall");
+            self.busy.set(false);
+        }
+    }
+    pub fn set_value_sync(&self, value: i32) {
+        self.upcall_on_command.set(Some(value));
+    }
+}
+
+impl crate::fake::SyscallDriver for Humidity {
+    fn info(&self) -> DriverInfo {
+        DriverInfo::new(DRIVER_NUM).upcall_count(1)
+    }
+
+    fn register(&self, share_ref: DriverShareRef) {
+        self.share_ref.replace(share_ref);
+    }
+
+    fn command(&self, command_id: u32, _argument0: u32, _argument1: u32) -> CommandReturn {
+        match command_id {
+            EXISTS => crate::command_return::success(),
+
+            READ_HUM => {
+                if self.busy.get() {
+                    return crate::command_return::failure(ErrorCode::Busy);
+                }
+                self.busy.set(true);
+                if let Some(val) = self.upcall_on_command.take() {
+                    self.set_value(val);
+                }
+                crate::command_return::success()
+            }
+            _ => crate::command_return::failure(ErrorCode::NoSupport),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests;
+// -----------------------------------------------------------------------------
+// Driver number and command IDs
+// -----------------------------------------------------------------------------
+
+const DRIVER_NUM: u32 = 0x60001;
+
+// Command IDs
+
+const EXISTS: u32 = 0;
+const READ_HUM: u32 = 1;
diff --git a/unittest/src/fake/humidity/tests.rs b/unittest/src/fake/humidity/tests.rs
new file mode 100644
index 00000000..31501537
--- /dev/null
+++ b/unittest/src/fake/humidity/tests.rs
@@ -0,0 +1,67 @@
+use crate::fake::{self, SyscallDriver};
+use fake::humidity::*;
+use libtock_platform::{share, DefaultConfig, YieldNoWaitReturn};
+
+//Test the command implementation
+#[test]
+fn command() {
+    let hum = Humidity::new();
+
+    assert!(hum.command(EXISTS, 1, 2).is_success());
+
+    assert!(hum.command(READ_HUM, 0, 0).is_success());
+
+    assert_eq!(
+        hum.command(READ_HUM, 0, 0).get_failure(),
+        Some(ErrorCode::Busy)
+    );
+
+    hum.set_value(100);
+    assert!(hum.command(READ_HUM, 0, 1).is_success());
+    hum.set_value(100);
+
+    hum.set_value_sync(100);
+    assert!(hum.command(READ_HUM, 0, 1).is_success());
+    assert!(hum.command(READ_HUM, 0, 1).is_success());
+}
+
+// Integration test that verifies Humidity works with fake::Kernel and
+// libtock_platform::Syscalls.
+#[test]
+fn kernel_integration() {
+    use libtock_platform::Syscalls;
+    let kernel = fake::Kernel::new();
+    let hum = Humidity::new();
+    kernel.add_driver(&hum);
+    assert!(fake::Syscalls::command(DRIVER_NUM, EXISTS, 1, 2).is_success());
+    assert!(fake::Syscalls::command(DRIVER_NUM, READ_HUM, 0, 0).is_success());
+    assert_eq!(
+        fake::Syscalls::command(DRIVER_NUM, READ_HUM, 0, 0).get_failure(),
+        Some(ErrorCode::Busy)
+    );
+    hum.set_value(100);
+    assert!(fake::Syscalls::command(DRIVER_NUM, READ_HUM, 0, 1).is_success());
+
+    let listener = Cell::<Option<(u32,)>>::new(None);
+    share::scope(|subscribe| {
+        assert_eq!(
+            fake::Syscalls::subscribe::<_, _, DefaultConfig, DRIVER_NUM, 0>(subscribe, &listener),
+            Ok(())
+        );
+
+        hum.set_value(100);
+        assert_eq!(fake::Syscalls::yield_no_wait(), YieldNoWaitReturn::Upcall);
+        assert_eq!(listener.get(), Some((100,)));
+
+        hum.set_value(200);
+        assert_eq!(fake::Syscalls::yield_no_wait(), YieldNoWaitReturn::NoUpcall);
+
+        assert!(fake::Syscalls::command(DRIVER_NUM, READ_HUM, 0, 1).is_success());
+        hum.set_value(200);
+        assert_eq!(fake::Syscalls::yield_no_wait(), YieldNoWaitReturn::Upcall);
+
+        hum.set_value_sync(200);
+        assert!(fake::Syscalls::command(DRIVER_NUM, READ_HUM, 0, 1).is_success());
+        assert_eq!(fake::Syscalls::yield_no_wait(), YieldNoWaitReturn::Upcall);
+    });
+}
diff --git a/unittest/src/fake/mod.rs b/unittest/src/fake/mod.rs
index bf29e4ff..156616f5 100644
--- a/unittest/src/fake/mod.rs
+++ b/unittest/src/fake/mod.rs
@@ -13,6 +13,7 @@ mod alarm;
 mod buttons;
 mod console;
 mod gpio;
+mod humidity;
 mod kernel;
 mod leds;
 mod low_level_debug;
@@ -24,6 +25,7 @@ pub use alarm::Alarm;
 pub use buttons::Buttons;
 pub use console::Console;
 pub use gpio::{Gpio, GpioMode, InterruptEdge, PullMode};
+pub use humidity::Humidity;
 pub use kernel::Kernel;
 pub use leds::Leds;
 pub use low_level_debug::{LowLevelDebug, Message};