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Fix Hardwareserial sending a byte twice #3865

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Fix Hardwareserial sending a byte twice #3865

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9aa902e
Fix Hardwareserial sending a byte twice
NicoHood Sep 25, 2015
3076251
Changed Hardwareserial cli() to Atomic Blocks
NicoHood Sep 26, 2015
7b87a52
Made Serial.write() buffer comparison atomic
NicoHood Sep 26, 2015
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27 changes: 19 additions & 8 deletions hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include <util/atomic.h>
#include "Arduino.h"

#include "HardwareSerial.h"
Expand Down Expand Up @@ -178,13 +179,12 @@ int HardwareSerial::read(void)
int HardwareSerial::availableForWrite(void)
{
#if (SERIAL_TX_BUFFER_SIZE>256)
uint8_t oldSREG = SREG;
cli();
ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
#endif
tx_buffer_index_t head = _tx_buffer_head;
tx_buffer_index_t tail = _tx_buffer_tail;
#if (SERIAL_TX_BUFFER_SIZE>256)
SREG = oldSREG;
}
#endif
if (head >= tail) return SERIAL_TX_BUFFER_SIZE - 1 - head + tail;
return tail - head - 1;
Expand Down Expand Up @@ -217,9 +217,18 @@ size_t HardwareSerial::write(uint8_t c)
// to the data register and be done. This shortcut helps
// significantly improve the effective datarate at high (>
// 500kbit/s) bitrates, where interrupt overhead becomes a slowdown.
if (_tx_buffer_head == _tx_buffer_tail && bit_is_set(*_ucsra, UDRE0)) {
*_udr = c;
sbi(*_ucsra, TXC0);
#if (SERIAL_TX_BUFFER_SIZE>256)
ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
#endif
bool emptyBuffer = _tx_buffer_head == _tx_buffer_tail;
#if (SERIAL_TX_BUFFER_SIZE>256)
}
#endif
if (emptyBuffer && bit_is_set(*_ucsra, UDRE0)) {
ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
*_udr = c;
sbi(*_ucsra, TXC0);
}
return 1;
}
tx_buffer_index_t i = (_tx_buffer_head + 1) % SERIAL_TX_BUFFER_SIZE;
Expand All @@ -240,9 +249,11 @@ size_t HardwareSerial::write(uint8_t c)
}

_tx_buffer[_tx_buffer_head] = c;
_tx_buffer_head = i;
ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
_tx_buffer_head = i;

sbi(*_ucsrb, UDRIE0);
sbi(*_ucsrb, UDRIE0);
}

return 1;
}
Expand Down