Add delay function to platform layer. (aws#235)

Author: gordonwang0

PortingGuide.md

@@ -15,8 +15,8 @@ Current SDK Directory Layout (mbedTLS)
 |--`include` (Header files of the AWS IoT device SDK) <br>
 |--`src` (Source files of the AWS IoT device SDK) <br>
 |--`platform` (Platform specific files) <br>
-|--`samples` (Samples including makefiles for building on mbedTLS) <br> 
-|--`tests` (Tests for verifying SDK is functioning as expected) <br> 
+|--`samples` (Samples including makefiles for building on mbedTLS) <br>
+|--`tests` (Tests for verifying SDK is functioning as expected) <br>
 
 All makefiles in this SDK were configured using the documented folder structure above, so moving or renaming folders will require modifications to makefiles.
 
@@ -44,7 +44,7 @@ This section explains the API calls that need to be implemented in order for the
 
 ### Timer Functions
 
-A timer implementation is necessary to handle request timeouts (sending MQTT connect, subscribe, etc. commands) as well as connection maintenance (MQTT keep-alive pings). Timers need millisecond resolution and are polled for expiration so these can be implemented using a "milliseconds since startup" free-running counter if desired. In the synchronous sample provided with this SDK only one command will be "in flight" at one point in time plus the client's ping timer. 
+A timer implementation is necessary to handle request timeouts (sending MQTT connect, subscribe, etc. commands) as well as connection maintenance (MQTT keep-alive pings). Timers need millisecond resolution and are polled for expiration so these can be implemented using a "milliseconds since startup" free-running counter if desired. In the synchronous sample provided with this SDK only one command will be "in flight" at one point in time plus the client's ping timer.
 
 Define the `Timer` Struct as in `timer_platform.h`
 
@@ -63,10 +63,13 @@ countdown_sec - set the timer to expire in x seconds and start the timer.
 `uint32_t left_ms(Timer *);`
 left_ms - query time in milliseconds left on the timer.
 
+`void delay(unsigned milliseconds)`
+delay - sleep for the specified number of milliseconds.
+
 
 ### Network Functions
 
-In order for the MQTT client stack to be able to communicate via the TCP/IP network protocol stack using a mutually authenticated TLS connection, the following API calls need to be implemented for your platform. 
+In order for the MQTT client stack to be able to communicate via the TCP/IP network protocol stack using a mutually authenticated TLS connection, the following API calls need to be implemented for your platform.
 
 For additional details about API parameters refer to the [API documentation](http://aws-iot-device-sdk-embedded-c-docs.s3-website-us-east-1.amazonaws.com/index.html).
 
@@ -76,7 +79,7 @@ This is used for data specific to the TLS library being used.
 `IoT_Error_t iot_tls_init(Network *pNetwork, char *pRootCALocation, char *pDeviceCertLocation,
   						 char *pDevicePrivateKeyLocation, char *pDestinationURL,
   						 uint16_t DestinationPort, uint32_t timeout_ms, bool ServerVerificationFlag);`
-Initialize the network client / structure.  
+Initialize the network client / structure.
 
 `IoT_Error_t iot_tls_connect(Network *pNetwork, TLSConnectParams *TLSParams);`
 Create a TLS TCP socket to the configure address using the credentials provided via the NewNetwork API call. This will include setting up certificate locations / arrays.
@@ -102,15 +105,15 @@ The TLS library generally provides the API for the underlying TCP socket.
 
 ### Threading Functions
 
-The MQTT client uses a state machine to control operations in multi-threaded situations. However it requires a mutex implementation to guarantee thread safety. This is not required in situations where thread safety is not important and it is disabled by default. The _ENABLE_THREAD_SUPPORT_ macro needs to be defined in aws_iot_config.h to enable this layer. You will also need to add the -lpthread linker flag for the compiler if you are using the provided reference implementation.   
+The MQTT client uses a state machine to control operations in multi-threaded situations. However it requires a mutex implementation to guarantee thread safety. This is not required in situations where thread safety is not important and it is disabled by default. The _ENABLE_THREAD_SUPPORT_ macro needs to be defined in aws_iot_config.h to enable this layer. You will also need to add the -lpthread linker flag for the compiler if you are using the provided reference implementation.
 
 For additional details about API parameters refer to the [API documentation](http://aws-iot-device-sdk-embedded-c-docs.s3-website-us-east-1.amazonaws.com/index.html).
 
 Define the `IoT_Mutex_t` Struct as in `threads_platform.h`
 This is used for data specific to the TLS library being used.
 
 `IoT_Error_t aws_iot_thread_mutex_init(IoT_Mutex_t *);`
-Initialize the mutex provided as argument.  
+Initialize the mutex provided as argument.
 
 `IoT_Error_t aws_iot_thread_mutex_lock(IoT_Mutex_t *);`
 Lock the mutex provided as argument
@@ -125,7 +128,7 @@ The threading layer provides the implementation of mutexes used for thread-safe
 
 ### Sample Porting:
 
-Marvell has ported the SDK for their development boards. [These](https://github.com/marvell-iot/aws_starter_sdk/tree/master/sdk/external/aws_iot/platform/wmsdk) files are example implementations of the above mentioned functions. 
+Marvell has ported the SDK for their development boards. [These](https://github.com/marvell-iot/aws_starter_sdk/tree/master/sdk/external/aws_iot/platform/wmsdk) files are example implementations of the above mentioned functions.
 This provides a port of the timer and network layer. The threading layer is not a part of this port.
 
 ## Time source for certificate validation

platform/linux/common/timer.c

@@ -26,6 +26,7 @@ extern "C" {
 #include <sys/types.h>
 #include <stdint.h>
 #include <stdbool.h>
+#include <unistd.h>
 
 #include "timer_platform.h"
 
@@ -69,6 +70,13 @@ void init_timer(Timer *timer) {
 	timer->end_time = (struct timeval) {0, 0};
 }
 
+void delay(unsigned milliseconds)
+{
+	useconds_t sleepTime = (useconds_t)(milliseconds * 1000);
+
+	usleep(sleepTime);
+}
+
 #ifdef __cplusplus
 }
 #endif

platform/linux/common/timer_platform.h

@@ -34,6 +34,13 @@ struct Timer {
 	struct timeval end_time;
 };
 
+/**
+ * @brief Delay (sleep) for the specified number of milliseconds.
+ *
+ * @param milliseconds The number of milliseconds to sleep.
+ */
+void delay(unsigned milliseconds);
+
 #ifdef __cplusplus
 }
 #endif