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Remove very bad loop in Serial transmit driver that causes the CPU #42

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Merged
merged 5 commits into from
Aug 19, 2019
Merged

Remove very bad loop in Serial transmit driver that causes the CPU #42

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525bb7d
Remove very bad loop in Serial transmit driver that causes the CPU
egilkv Aug 2, 2019
8462a25
Make one common method to handle the interrupt emulation,
egilkv Aug 2, 2019
106efcf
Remove comment no longer valid
egilkv Aug 4, 2019
08e530f
Improve name of DRE polling function
egilkv Aug 5, 2019
3b23183
Formatting according to Arduino standards
egilkv Aug 6, 2019
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36 changes: 19 additions & 17 deletions cores/arduino/UART.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -88,7 +88,6 @@ void serialEventRun(void)
void UartClass::_tx_data_empty_irq(void)
{
// Check if tx buffer already empty.
// This interrupt-handler can be called "manually" from flush();
if (_tx_buffer_head == _tx_buffer_tail) {
// Buffer empty, so disable "data register empty" interrupt
(*_hwserial_module).CTRLA &= (~USART_DREIE_bm);
Expand All @@ -107,8 +106,6 @@ void UartClass::_tx_data_empty_irq(void)

(*_hwserial_module).TXDATAL = c;

while(!((*_hwserial_module).STATUS & USART_DREIF_bm));

if (_tx_buffer_head == _tx_buffer_tail) {
// Buffer empty, so disable "data register empty" interrupt
(*_hwserial_module).CTRLA &= (~USART_DREIE_bm);
Expand All @@ -121,6 +118,22 @@ void UartClass::_tx_data_empty_irq(void)
}
}

// To invoke data empty "interrupt" via a call, use this method
void UartClass::_poll_tx_data_empty(void) {
if ( (!(SREG & CPU_I_bm)) || (!((*_hwserial_module).CTRLA & USART_DREIE_bm)) ) {
// Interrupts are disabled either globally or for data register empty,
// so we'll have to poll the "data register empty" flag ourselves.
// If it is set, pretend an interrupt has happened and call the handler
//to free up space for us.

// Invoke interrupt handler only if conditions data register is empty
if ((*_hwserial_module).STATUS & USART_DREIF_bm) {
_tx_data_empty_irq();
}
}
// In case interrupts are enabled, the interrupt routine will be invoked by itself
}

// Public Methods //////////////////////////////////////////////////////////////

void UartClass::begin(unsigned long baud, uint16_t config)
Expand Down Expand Up @@ -253,9 +266,7 @@ void UartClass::flush()

// If interrupts are globally disabled or the and DR empty interrupt is disabled,
// poll the "data register empty" interrupt flag to prevent deadlock
if ( (!(SREG & CPU_I_bm)) || (!((*_hwserial_module).CTRLA & USART_DREIE_bm)) ) {
_tx_data_empty_irq();
}
_poll_tx_data_empty();
}
// If we get here, nothing is queued anymore (DREIE is disabled) and
// the hardware finished transmission (TXCIF is set).
Expand Down Expand Up @@ -294,18 +305,9 @@ size_t UartClass::write(uint8_t c)
tx_buffer_index_t i = (_tx_buffer_head + 1) % SERIAL_TX_BUFFER_SIZE;

//If the output buffer is full, there's nothing for it other than to
//wait for the interrupt handler to empty it a bit
//wait for the interrupt handler to empty it a bit (or emulate interrupts)
while (i == _tx_buffer_tail) {
if ( ( !(SREG & CPU_I_bm) ) || ( !((*_hwserial_module).CTRLA & USART_DREIE_bm) ) ) {
// Interrupts are disabled either globally or for data register empty,
// so we'll have to poll the "data register empty" flag ourselves.
// If it is set, pretend an interrupt has happened and call the handler
//to free up space for us.

_tx_data_empty_irq();
} else {
// nop, the interrupt handler will free up space for us
}
_poll_tx_data_empty();
}

_tx_buffer[_tx_buffer_head] = c;
Expand Down
2 changes: 2 additions & 0 deletions cores/arduino/UART.h
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Original file line number Diff line number Diff line change
Expand Up @@ -169,6 +169,8 @@ class UartClass : public HardwareSerial
// Interrupt handlers - Not intended to be called externally
inline void _rx_complete_irq(void);
void _tx_data_empty_irq(void);
private:
void _poll_tx_data_empty(void);
};

#if defined(HWSERIAL0)
Expand Down