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add support for different serial formats #63

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206 changes: 176 additions & 30 deletions AltSoftSerial.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -59,15 +59,20 @@ static volatile uint8_t tx_buffer_head;
static volatile uint8_t tx_buffer_tail;
#define TX_BUFFER_SIZE 68
static volatile uint8_t tx_buffer[TX_BUFFER_SIZE];
static uint8_t tx_parity;

static uint8_t data_bits, stop_bits;
static uint8_t parity; // 0 for none, 1 for odd, 2 for even
static uint8_t total_bits, almost_total_bits; // these are sums calculated during .begin() to speed up the loop in ISR(CAPTURE_INTERRUPT)
static uint8_t byte_alignment;

#ifndef INPUT_PULLUP
#define INPUT_PULLUP INPUT
#endif

#define MAX_COUNTS_PER_BIT 6241 // 65536 / 10.5

void AltSoftSerial::init(uint32_t cycles_per_bit)
void AltSoftSerial::init(uint32_t cycles_per_bit, uint8_t config)
{
//Serial.printf("cycles_per_bit = %d\n", cycles_per_bit);
if (cycles_per_bit < MAX_COUNTS_PER_BIT) {
Expand Down Expand Up @@ -100,7 +105,14 @@ void AltSoftSerial::init(uint32_t cycles_per_bit)
}
}
ticks_per_bit = cycles_per_bit;
rx_stop_ticks = cycles_per_bit * 37 / 4;
/* [2019-08-11, stattin42]: Length of frame depends on total number of symbols/bits.
Need to adjust for number of data bits and parity bits. If not, start bit may be missed
for short formats if msb is a 1. In this case there is no edge between data/parity and
stop bit --> no capture interrupt --> relies on timer interrupt. Have not looked into
aspects of longer formats. */
// rx_stop_ticks = cycles_per_bit * 37 / 4;
setBitCounts(config); // total_bits are calculated here
rx_stop_ticks = cycles_per_bit * ((4*(total_bits))+1)/4;
pinMode(INPUT_CAPTURE_PIN, INPUT_PULLUP);
digitalWrite(OUTPUT_COMPARE_A_PIN, HIGH);
pinMode(OUTPUT_COMPARE_A_PIN, OUTPUT);
Expand Down Expand Up @@ -144,14 +156,15 @@ void AltSoftSerial::writeByte(uint8_t b)
tx_state = 1;
tx_byte = b;
tx_bit = 0;
if (parity)
tx_parity = parity_even_bit(b) == (parity==2);
ENABLE_INT_COMPARE_A();
CONFIG_MATCH_CLEAR();
SET_COMPARE_A(GET_TIMER_COUNT() + 16);
}
SREG = intr_state;
}


ISR(COMPARE_A_INTERRUPT)
{
uint8_t state, byte, bit, head, tail;
Expand All @@ -160,15 +173,22 @@ ISR(COMPARE_A_INTERRUPT)
state = tx_state;
byte = tx_byte;
target = GET_COMPARE_A();
while (state < 10) {
target += ticks_per_bit;
if (state < 9)
bit = byte & 1;
else
bit = 1; // stopbit
byte >>= 1;
while (state < 11) {
target += ticks_per_bit; // Bit start time
if (state < 9) {
bit = byte & 1; // data bit
byte >>= 1;
} else {
if (state == 9) {
bit = tx_parity; // parity bit
} else {
bit = 1; // stop bit
}
}
state++;
if (bit != tx_bit) {
if (state == (data_bits+1))
state = 9 + !parity;
if (bit != tx_bit) { // schedule flip of output for bit starting at time target
if (bit) {
CONFIG_MATCH_SET();
} else {
Expand All @@ -185,10 +205,10 @@ ISR(COMPARE_A_INTERRUPT)
head = tx_buffer_head;
tail = tx_buffer_tail;
if (head == tail) {
if (state == 10) {
if (state == 11) {
// Wait for final stop bit to finish
tx_state = 11;
SET_COMPARE_A(target + ticks_per_bit);
tx_state = 12;
SET_COMPARE_A(target + (stop_bits * ticks_per_bit));
} else {
tx_state = 0;
CONFIG_MATCH_NORMAL();
Expand All @@ -199,9 +219,11 @@ ISR(COMPARE_A_INTERRUPT)
tx_buffer_tail = tail;
tx_byte = tx_buffer[tail];
tx_bit = 0;
if (parity)
tx_parity = parity_even_bit(tx_byte) == (parity==2);
CONFIG_MATCH_CLEAR();
if (state == 10)
SET_COMPARE_A(target + ticks_per_bit);
if (state == 11)
SET_COMPARE_A(target + (stop_bits * ticks_per_bit));
else
SET_COMPARE_A(GET_TIMER_COUNT() + 16);
tx_state = 1;
Expand Down Expand Up @@ -249,16 +271,24 @@ ISR(CAPTURE_INTERRUPT)
while (1) {
offset = capture - target;
if (offset > offset_overflow) break;
rx_byte = (rx_byte >> 1) | rx_bit;
if (state <= data_bits) // only store data bits
rx_byte = (rx_byte >> 1) | rx_bit;
target += ticks_per_bit;
state++;
if (state >= 9) {
if (state > almost_total_bits) {
DISABLE_INT_COMPARE_B();
head = rx_buffer_head + 1;
if (head >= RX_BUFFER_SIZE) head = 0;
if (head != rx_buffer_tail) {
rx_buffer[head] = rx_byte;
rx_buffer_head = head;
/* [2019-08-11, stattin42]: Bits in rx_byte are in correct
position only for 8-bit data format. For less than 8 bits,
rx_byte needs to be shifted for LS bit to get to bit0 location.
Added byte_alignment variable for speed: */
rx_byte = rx_byte>>byte_alignment;
if (!parity || (parity_even_bit(rx_byte) == (parity==2)) == (bool)rx_bit) {
head = rx_buffer_head + 1;
if (head >= RX_BUFFER_SIZE) head = 0;
if (head != rx_buffer_tail) {
rx_buffer[head] = rx_byte;
rx_buffer_head = head;
}
}
CONFIG_CAPTURE_FALLING_EDGE();
rx_bit = 0;
Expand All @@ -280,15 +310,21 @@ ISR(COMPARE_B_INTERRUPT)
CONFIG_CAPTURE_FALLING_EDGE();
state = rx_state;
bit = rx_bit ^ 0x80;
while (state < 9) {
while (state <= data_bits) {
rx_byte = (rx_byte >> 1) | bit;
state++;
}
head = rx_buffer_head + 1;
if (head >= RX_BUFFER_SIZE) head = 0;
if (head != rx_buffer_tail) {
rx_buffer[head] = rx_byte;
rx_buffer_head = head;
/* [2019-08-11, stattin42]: Bits in rx_byte are in correct position only for 8-bit
data format. For less than 8 bits, rx_byte needs to be shifted for LS bit to get to
bit0 location. Added byte_alignment variable for speed: */
rx_byte = rx_byte>>byte_alignment;
if (!parity || (parity_even_bit(rx_byte) == (parity==2)) == (bool)bit) {
head = rx_buffer_head + 1;
if (head >= RX_BUFFER_SIZE) head = 0;
if (head != rx_buffer_tail) {
rx_buffer[head] = rx_byte;
rx_buffer_head = head;
}
}
rx_state = 0;
CONFIG_CAPTURE_FALLING_EDGE();
Expand Down Expand Up @@ -339,13 +375,123 @@ int AltSoftSerial::availableForWrite(void)

if (tail > head) return tail - head;
return TX_BUFFER_SIZE + tail - head;
};
}

void AltSoftSerial::flushInput(void)
{
rx_buffer_head = rx_buffer_tail;
}

void AltSoftSerial::setBitCounts(uint8_t config) {
parity = 0;
stop_bits = 1;
switch (config) {
case SERIAL_5N1:
data_bits = 5;
break;
case SERIAL_6N1:
data_bits = 6;
break;
case SERIAL_7N1:
data_bits = 7;
break;
case SERIAL_8N1:
data_bits = 8;
break;
case SERIAL_5N2:
data_bits = 5;
stop_bits = 2;
break;
case SERIAL_6N2:
data_bits = 6;
stop_bits = 2;
break;
case SERIAL_7N2:
data_bits = 7;
stop_bits = 2;
break;
case SERIAL_8N2:
data_bits = 8;
stop_bits = 2;
break;
case SERIAL_5O1:
parity = 1;
data_bits = 5;
break;
case SERIAL_6O1:
parity = 1;
data_bits = 6;
break;
case SERIAL_7O1:
parity = 1;
data_bits = 7;
break;
case SERIAL_8O1:
parity = 1;
data_bits = 8;
break;
case SERIAL_5O2:
parity = 1;
data_bits = 5;
stop_bits = 2;
break;
case SERIAL_6O2:
parity = 1;
data_bits = 6;
stop_bits = 2;
break;
case SERIAL_7O2:
parity = 1;
data_bits = 7;
stop_bits = 2;
break;
case SERIAL_8O2:
parity = 1;
data_bits = 8;
stop_bits = 2;
break;
case SERIAL_5E1:
parity = 2;
data_bits = 5;
break;
case SERIAL_6E1:
parity = 2;
data_bits = 6;
break;
case SERIAL_7E1:
parity = 2;
data_bits = 7;
break;
case SERIAL_8E1:
parity = 2;
data_bits = 8;
break;
case SERIAL_5E2:
parity = 2;
data_bits = 5;
stop_bits = 2;
break;
case SERIAL_6E2:
parity = 2;
data_bits = 6;
stop_bits = 2;
break;
case SERIAL_7E2:
parity = 2;
data_bits = 7;
stop_bits = 2;
break;
case SERIAL_8E2:
parity = 2;
data_bits = 8;
stop_bits = 2;
break;
}

total_bits = data_bits + (parity ? 1 : 0) + stop_bits;
almost_total_bits = total_bits - stop_bits;
byte_alignment = 8-data_bits;
}

#ifdef ALTSS_USE_FTM0
void ftm0_isr(void)
Expand Down
6 changes: 4 additions & 2 deletions AltSoftSerial.h
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@
#define AltSoftSerial_h

#include <inttypes.h>
#include <util/parity.h>

#if ARDUINO >= 100
#include "Arduino.h"
Expand All @@ -44,7 +45,7 @@ class AltSoftSerial : public Stream
public:
AltSoftSerial() { }
~AltSoftSerial() { end(); }
static void begin(uint32_t baud) { init((ALTSS_BASE_FREQ + baud / 2) / baud); }
static void begin(uint32_t baud, uint8_t config = SERIAL_8N1) { init((ALTSS_BASE_FREQ + baud / 2) / baud, config); }
static void end();
int peek();
int read();
Expand All @@ -69,8 +70,9 @@ class AltSoftSerial : public Stream
static void enable_timer0(bool enable) { (void)enable; }
static bool timing_error;
private:
static void init(uint32_t cycles_per_bit);
static void init(uint32_t cycles_per_bit, uint8_t config);
static void writeByte(uint8_t byte);
static void setBitCounts(uint8_t config);
};

#endif