noisymime
/
ArduinoCore-avr
mirror of https://github.com/noisymime/ArduinoCore-avr.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

make serial.available, peek, read atomic 

when SERIAL_RX_BUFFER_SIZE is defined as greater than 256, the current HardwareSerial.cpp code almost works correctly. but not quite. the function serial.available may return an incorrect number of characters waiting (though when treated purely as a boolean it seems not to fault).serial.peek has a similar issue detecting if a character is waiting, while serial.read may also leave _rx_buffer_tail corrupt to an interrupt occurring mid-update (this corruption may cause the ISR to be mistaken about how much free is available in the Rx buffer).

the proposed changes to these three functions add cli/sti pairings around the critical pieces of code. i have tested and verified the change made to serial.available as correcting the problem, while the change to serial.peek follows the exact same pattern. the changes to serial.read have been confirmed as not breaking the function, but i have not been in a position to test the failure of the original (non-atomic) version to make comparisons.

multiple testing was conducted at 115,200 baud and 500,000 baud using data streams of 1,000,000 characters sent over a 2 minute interval. any error causing loss of character would have resulted in a catastrophic (ie, very obvious) failure.

cheers,
rob   :-)

-> Squash and rebase of https://github.com/arduino/Arduino/pull/3848
This commit is contained in:
robert rozee 2017-11-13 17:03:55 +01:00 committed by Martino Facchin
parent b084848f2e
commit 95bb83ef96
1 changed files with 42 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
cores/arduino/HardwareSerial.cpp
View File

@ -151,26 +151,62 @@ void HardwareSerial::end()
int HardwareSerial::available(void)
{
return ((unsigned int)(SERIAL_RX_BUFFER_SIZE + _rx_buffer_head - _rx_buffer_tail)) % SERIAL_RX_BUFFER_SIZE;
#if (SERIAL_RX_BUFFER_SIZE>256)
uint8_t oldSREG = SREG; // save interrupt flag
cli(); // disable interrupts
#endif
rx_buffer_index_t head = _rx_buffer_head; // retrieve Rx head index
rx_buffer_index_t tail = _rx_buffer_tail; // retrieve Rx tail index
#if (SERIAL_RX_BUFFER_SIZE>256)
SREG = oldSREG; // restore the interrupt flag
#endif
return ((unsigned int)(SERIAL_RX_BUFFER_SIZE + head - tail)) % SERIAL_RX_BUFFER_SIZE;
}
int HardwareSerial::peek(void)
{
if (_rx_buffer_head == _rx_buffer_tail) {
#if (SERIAL_RX_BUFFER_SIZE>256)
uint8_t oldSREG = SREG; // save interrupt flag
cli(); // disable interrupts
#endif
rx_buffer_index_t head = _rx_buffer_head; // retrieve Rx head index
rx_buffer_index_t tail = _rx_buffer_tail; // retrieve Rx tail index
#if (SERIAL_RX_BUFFER_SIZE>256)
SREG = oldSREG; // restore the interrupt flag
#endif
if (head == tail) {
return -1;
} else {
return _rx_buffer[_rx_buffer_tail];
return _rx_buffer[tail];
}
}
int HardwareSerial::read(void)
{
// if the head isn't ahead of the tail, we don't have any characters
if (_rx_buffer_head == _rx_buffer_tail) {
#if (SERIAL_RX_BUFFER_SIZE>256)
uint8_t oldSREG = SREG; // save interrupt flag
cli(); // disable interrupts
#endif
rx_buffer_index_t head = _rx_buffer_head; // retrieve Rx head index
rx_buffer_index_t tail = _rx_buffer_tail; // retrieve Rx tail index
#if (SERIAL_RX_BUFFER_SIZE>256)
SREG = oldSREG; // restore the interrupt flag
#endif
if (head == tail) {
return -1;
} else {
unsigned char c = _rx_buffer[_rx_buffer_tail];
_rx_buffer_tail = (rx_buffer_index_t)(_rx_buffer_tail + 1) % SERIAL_RX_BUFFER_SIZE;
unsigned char c = _rx_buffer[tail];
#if (SERIAL_RX_BUFFER_SIZE>256)
uint8_t oldSREG = SREG; // save interrupt flag
cli(); // disable interrupts
#endif
_rx_buffer_tail = (tail + 1) % SERIAL_RX_BUFFER_SIZE;
#if (SERIAL_RX_BUFFER_SIZE>256)
SREG = oldSREG; // restore the interrupt flag
#endif
return c;
}
}