8000 rp2pio: Transfer up to 32 bytes before checking background tasks by jepler · Pull Request #4155 · adafruit/circuitpython · GitHub
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rp2pio: Transfer up to 32 bytes before checking background tasks #4155

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Merged
merged 1 commit into from
Feb 8, 2021
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rp2pio: Transfer up to 32 bytes before checking background tasks #4155

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26 changes: 17 additions & 9 deletions ports/raspberrypi/common-hal/rp2pio/StateMachine.c
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Original file line number Diff line number Diff line change
Expand Up @@ -546,15 +546,23 @@ static bool _transfer(rp2pio_statemachine_obj_t *self,
size_t tx_remaining = out_len;

while (rx_remaining || tx_remaining) {
if (tx_remaining && !pio_sm_is_tx_fifo_full(self->pio, self->state_machine)) {
*tx_destination = *data_out;
data_out++;
--tx_remaining;
}
if (rx_remaining && !pio_sm_is_rx_fifo_empty(self->pio, self->state_machine)) {
*data_in = (uint8_t) *rx_source;
data_in++;
--rx_remaining;
for (int i=0; i<32; i++) {
bool did_transfer = false;
if (tx_remaining && !pio_sm_is_tx_fifo_full(self->pio, self->state_machine)) {
*tx_destination = *data_out;
data_out++;
--tx_remaining;
did_transfer = true;
}
if (rx_remaining && !pio_sm_is_rx_fifo_empty(self->pio, self->state_machine)) {
*data_in = (uint8_t) *rx_source;
data_in++;
--rx_remaining;
did_transfer = true;
}
if (!did_transfer) {
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I think it'd be clearer if you replaced the original if statements with while loops. That way you'd load up the 4 or 8 entry FIFO and then move on. 32 seems arbitrary and I'm skeptical you'd ever hit that many due to the FIFO size.

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I chose 32 because it was the DMA threshold. I didn't check the FIFO size at all! I'll open an issue suggesting the clean-up, but try to get to it next time I'm working in this code.

break;
}
}
RUN_BACKGROUND_TASKS;
if (mp_hal_is_interrupted()) {
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