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Fix display glitch during neopixel update #10600

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Merged
dhalbert merged 1 commit into from
Aug 29, 2025
Merged

Fix display glitch during neopixel update #10600

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90 changes: 71 additions & 19 deletions ports/raspberrypi/common-hal/rp2pio/StateMachine.c
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Original file line number Diff line number Diff line change
Expand Up @@ -853,32 +853,77 @@ static bool _transfer(rp2pio_statemachine_obj_t *self,
// This implementation is based on SPI but varies because the tx and rx buffers
// may be different lengths and occur at different times or speeds.

// Use DMA for large transfers if channels are available.
// Don't exceed FIFO size.
const size_t dma_min_size_threshold = self->fifo_depth;
int chan_tx = -1;
int chan_rx = -1;
size_t len = MAX(out_len, in_len);
bool tx = data_out != NULL;
bool rx = data_in != NULL;
bool use_dma = len >= dma_min_size_threshold || swap_out || swap_in;
bool free_data_out = false;
bool free_data_in = false;
uint8_t *sram_data_out = (uint8_t *)data_out;
uint8_t *sram_data_in = data_in;
bool tx_fits_in_fifo = (out_len / out_stride_in_bytes) <= self->fifo_depth;
bool rx_fits_in_fifo = (in_len / in_stride_in_bytes) <= self->fifo_depth;
bool use_dma = !(tx_fits_in_fifo && rx_fits_in_fifo) || swap_out || swap_in;

if (use_dma) {
// Use DMA channels to service the two FIFOs
// We can only reliably use DMA for SRAM buffers. So, if we're given PSRAM buffers,
// then copy them to SRAM first. If we can't, then fail.
// Use DMA channels to service the two FIFOs. Fail if we can't allocate DMA channels.
if (tx) {
if (data_out < (uint8_t *)SRAM_BASE) {
// Try to allocate a temporary buffer for DMA transfer
uint8_t *temp_buffer = (uint8_t *)port_malloc(len, true);
if (temp_buffer == NULL) {
mp_printf(&mp_plat_print, "Failed to allocate temporary buffer for DMA tx\n");
return false;
}
memcpy(temp_buffer, data_out, len);
sram_data_out = temp_buffer;
free_data_out = true;
}
chan_tx = dma_claim_unused_channel(false);
// DMA allocation failed...
if (chan_tx < 0) {
if (free_data_out) {
port_free(sram_data_out);
}
if (free_data_in) {
port_free(sram_data_in);
}
return false;
}
}
if (rx) {
if (data_in < (uint8_t *)SRAM_BASE) {
// Try to allocate a temporary buffer for DMA transfer
uint8_t *temp_buffer = (uint8_t *)port_malloc(len, true);
if (temp_buffer == NULL) {
mp_printf(&mp_plat_print, "Failed to allocate temporary buffer for DMA rx\n");
if (chan_tx >= 0) {
dma_channel_unclaim(chan_tx);
}
if (free_data_out) {
port_free(sram_data_out);
}
return false;
}
sram_data_in = temp_buffer;
free_data_in = true;
}
chan_rx = dma_claim_unused_channel(false);
// DMA allocation failed...
if (chan_rx < 0) {
// may need to free tx channel
if (chan_tx >= 0) {
dma_channel_unclaim(chan_tx);
}
if (free_data_out) {
port_free(sram_data_out);
}
if (free_data_in) {
port_free(sram_data_in);
}
return false;
}
}
Expand Down Expand Up @@ -910,7 +955,7 @@ static bool _transfer(rp2pio_statemachine_obj_t *self,
channel_config_set_bswap(&c, swap_out);
dma_channel_configure(chan_tx, &c,
tx_destination,
data_out,
sram_data_out,
out_len / out_stride_in_bytes,
false);
channel_mask |= 1u << chan_tx;
Expand All @@ -923,7 +968,7 @@ static bool _transfer(rp2pio_statemachine_obj_t *self,
channel_config_set_write_increment(&c, true);
channel_config_set_bswap(&c, swap_in);
dma_channel_configure(chan_rx, &c,
data_in,
sram_data_in,
rx_source,
in_len / in_stride_in_bytes,
false);
Expand All @@ -950,8 +995,7 @@ static bool _transfer(rp2pio_statemachine_obj_t *self,
self->pio->fdebug = stall_mask;
}

// If we have claimed only one channel successfully, we should release immediately. This also
// releases the DMA after use_dma has been done.
// Release the DMA channels after use_dma has been done.
if (chan_rx >= 0) {
dma_channel_unclaim(chan_rx);
}
Expand All @@ -960,31 +1004,31 @@ static bool _transfer(rp2pio_statemachine_obj_t *self,
}

if (!use_dma && !(self->user_interruptible && mp_hal_is_interrupted())) {
// Use software for small transfers, or if couldn't claim two DMA channels
// Use software for small transfers
size_t rx_remaining = in_len / in_stride_in_bytes;
size_t tx_remaining = out_len / out_stride_in_bytes;

while (rx_remaining || tx_remaining) {
while (tx_remaining && !pio_sm_is_tx_fifo_full(self->pio, self->state_machine)) {
if (out_stride_in_bytes == 1) {
*tx_destination = *data_out;
*tx_destination = *sram_data_out;
} else if (out_stride_in_bytes == 2) {
*((uint16_t *)tx_destination) = *((uint16_t *)data_out);
*((uint16_t *)tx_destination) = *((uint16_t *)sram_data_out);
} else if (out_stride_in_bytes == 4) {
*((uint32_t *)tx_destination) = *((uint32_t *)data_out);
*((uint32_t *)tx_destination) = *((uint32_t *)sram_data_out);
}
data_out += out_stride_in_bytes;
sram_data_out += out_stride_in_bytes;
--tx_remaining;
}
while (rx_remaining && !pio_sm_is_rx_fifo_empty(self->pio, self->state_machine)) {
if (in_stride_in_bytes == 1) {
*data_in = (uint8_t)*rx_source;
*sram_data_in = (uint8_t)*rx_source;
} else if (in_stride_in_bytes == 2) {
*((uint16_t *)data_in) = *((uint16_t *)rx_source);
*((uint16_t *)sram_data_in) = *((uint16_t *)rx_source);
} else if (in_stride_in_bytes == 4) {
*((uint32_t *)data_in) = *((uint32_t *)rx_source);
*((uint32_t *)sram_data_in) = *((uint32_t *)rx_source);
}
data_in += in_stride_in_bytes;
sram_data_in += in_stride_in_bytes;
--rx_remaining;
}
RUN_BACKGROUND_TASKS;
Expand All @@ -996,7 +1040,7 @@ static bool _transfer(rp2pio_statemachine_obj_t *self,
self->pio->fdebug = stall_mask;
}
// Wait for the state machine to finish transmitting the data we've queued
// up.
// up (either from the CPU or via DMA.)
if (tx) {
while (!pio_sm_is_tx_fifo_empty(self->pio, self->state_machine) ||
(self->wait_for_txstall && (self->pio->fdebug & stall_mask) == 0)) {
Expand All @@ -1006,6 +1050,14 @@ static bool _transfer(rp2pio_statemachine_obj_t *self,
}
}
}
if (free_data_out) {
port_free(sram_data_out);
}
if (free_data_in) {
// Copy the data from the SRAM buffer to the user PSRAM buffer.
memcpy(data_in, sram_data_in, len);
port_free(sram_data_in);
}
return true;
}

Expand Down