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samd51: Work around DMA hang #29

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Merged
merged 3 commits into from
Jan 2, 2020
Merged

samd51: Work around DMA hang #29

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168f636
dma: Add to a comment that misled me
jepler Dec 24, 2019
28ad937
dma: Detect hung audio DMA and restart it
jepler Dec 24, 2019
5ca3a8a
Clean up comments and dead code
jepler Dec 31, 2019
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45 changes: 30 additions & 15 deletions samd/dma.c
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Original file line number Diff line number Diff line change
Expand Up @@ -110,7 +110,6 @@ static int32_t shared_dma_transfer(void* peripheral,
} else {
#endif

// sercom index is incorrect for SAMD51
dma_configure(SHARED_TX_CHANNEL, sercom_index(peripheral) * 2 + FIRST_SERCOM_TX_TRIGSRC, false);
tx_active = true;
if (buffer_in != NULL) {
Expand Down Expand Up @@ -155,8 +154,6 @@ static int32_t shared_dma_transfer(void* peripheral,
if (sercom) {
SercomSpi *s = &((Sercom*) peripheral)->SPI;
s->INTFLAG.reg = SERCOM_SPI_INTFLAG_RXC | SERCOM_SPI_INTFLAG_DRE;
} else {
//QSPI->INTFLAG.reg = QSPI_INTFLAG_RXC | QSPI_INTFLAG_DRE;
}
// Start the RX job first so we don't miss the first byte. The TX job clocks
// the output.
Expand All @@ -168,23 +165,41 @@ static int32_t shared_dma_transfer(void* peripheral,
}


if (sercom) {
//DMAC->SWTRIGCTRL.reg |= (1 << SHARED_TX_CHANNEL);
} else {
// Do a manual copy to trigger then DMA. We do 32-bit accesses to match the DMA.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wcast-align"
if (!sercom) {
if (rx_active) {
//buffer_in[0] = *src;
DMAC->SWTRIGCTRL.reg |= (1 << SHARED_RX_CHANNEL);
} else {
//*(uint32_t*)dest = ((uint32_t*) buffer_out)[0];
}
#pragma GCC diagnostic pop
}

// Channels cycle between Suspend -> Pending -> Busy and back while transfering. So, we check
// the channels transfer status for an error or completion.
#ifdef SAMD51
// Sometimes (silicon bug?) this DMA transfer never starts, and another channel sits with
// CHSTATUS.reg = 0x3 (BUSY | PENDING). On the other hand, this is a
// legitimate state for a DMA channel to be in (apparently), so we can't use that alone as a check.
// Instead, let's look at the ACTIVE flag. When DMA is hung, everything in ACTIVE is zeros.
bool is_okay = false;
for (int i=0; i<10 && !is_okay; i++) {
bool complete = true;
if (rx_active) {
if (DMAC->Channel[SHARED_RX_CHANNEL].CHSTATUS.reg & 0x3)
complete = false;
}
if (tx_active) {
if (DMAC->Channel[SHARED_TX_CHANNEL].CHSTATUS.reg & 0x3)
complete = false;
}
is_okay = is_okay || (DMAC->ACTIVE.bit.ABUSY || complete);
}
if (!is_okay) {
for (int i=0; i<AUDIO_DMA_CHANNEL_COUNT; i++) {
if(DMAC->Channel[i].CHCTRLA.bit.ENABLE) {
DMAC->Channel[i].CHCTRLA.bit.ENABLE = 0;
DMAC->Channel[i].CHCTRLA.bit.ENABLE = 1;
}
}
}
#endif

// busy-wait for the RX and TX DMAs to either complete or encounter an error
if (rx_active) {
while ((dma_transfer_status(SHARED_RX_CHANNEL) & 0x3) == 0) {}
}
Expand Down