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Add documentation to dma_channel_abort regarding errata RP2040-E13 (#816)

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Co-authored-by: Luke Wren <wren6991@gmail.com>
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Graham Sanderson 2022-05-11 19:24:42 -05:00 committed by GitHub
parent 5a927792ef
commit 4e62c26a2c
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1 changed files with 27 additions and 1 deletions
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src/rp2_common/hardware_dma/include/hardware/dma.h
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@ -473,6 +473,32 @@ static inline void dma_channel_start(uint channel) {
* *
* Function will only return once the DMA has stopped. * Function will only return once the DMA has stopped.
* *
* Note that due to errata RP2040-E13, aborting a channel which has transfers
* in-flight (i.e. an individual read has taken place but the corresponding write has not), the ABORT
* status bit will clear prematurely, and subsequently the in-flight
* transfers will trigger a completion interrupt once they complete.
*
* The effect of this is that you \em may see a spurious completion interrupt
* on the channel as a result of calling this method.
*
* The calling code should be sure to ignore a completion IRQ as a result of this method. This may
* not require any additional work, as aborting a channel which may be about to complete, when you have a completion
* IRQ handler registered, is inherently race-prone, and so code is likely needed to disambiguate the two occurrences.
*
* If that is not the case, but you do have a channel completion IRQ handler registered, you can simply
* disable/re-enable the IRQ around the call to this method as shown by this code fragment (using DMA IRQ0).
*
* \code
* // disable the channel on IRQ0
* dma_channel_set_irq0_enabled(channel, false);
* // abort the channel
* dma_channel_abort(channel);
* // clear the spurious IRQ (if there was one)
* dma_channel_acknowledge_irq0(channel);
* // re-enable the channel on IRQ0
* dma_channel_set_irq0_enabled(channel, true);
*\endcode
*
* \param channel DMA channel * \param channel DMA channel
*/ */
static inline void dma_channel_abort(uint channel) { static inline void dma_channel_abort(uint channel) {
@ -480,7 +506,7 @@ static inline void dma_channel_abort(uint channel) {
dma_hw->abort = 1u << channel; dma_hw->abort = 1u << channel;
// Bit will go 0 once channel has reached safe state // Bit will go 0 once channel has reached safe state
// (i.e. any in-flight transfers have retired) // (i.e. any in-flight transfers have retired)
while (dma_hw->abort & (1ul << channel)) tight_loop_contents(); while (dma_hw->ch[channel].ctrl_trig & DMA_CH0_CTRL_TRIG_BUSY_BITS) tight_loop_contents();
} }
/*! \brief Enable single DMA channel's interrupt via DMA_IRQ_0 /*! \brief Enable single DMA channel's interrupt via DMA_IRQ_0