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[WIP]: PX4IO F7 DMA buffer review (dcache flush and alignment) #12075

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[WIP]: PX4IO F7 DMA buffer review (dcache flush and alignment) #12075

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2 changes: 1 addition & 1 deletion src/drivers/px4io/px4io_serial.h
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Original file line number Diff line number Diff line change
Expand Up @@ -252,7 +252,7 @@ class PX4IO_serial_f7 : public PX4IO_serial
/**
* IO Buffer storage
*/
static uint8_t _io_buffer_storage[];
static uint8_t _io_buffer_storage[] __attribute__((aligned(ARMV7M_DCACHE_LINESIZE)));
};

#else
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16 changes: 7 additions & 9 deletions src/drivers/px4io/px4io_serial_f7.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -57,12 +57,10 @@
#define rCR3 REG(STM32_USART_CR3_OFFSET)
#define rGTPR REG(STM32_USART_GTPR_OFFSET)

#define CACHE_LINE_SIZE 32
#define DMA_BUFFER_MASK (ARMV7M_DCACHE_LINESIZE - 1)
#define DMA_ALIGN_UP(n) (((n) + DMA_BUFFER_MASK) & ~DMA_BUFFER_MASK)

#define ROUND_UP_TO_POW2_CT(size, alignment) (((uintptr_t)((size) + ((alignment) - 1u))) & (~((uintptr_t)((alignment) - 1u))))
#define ALIGNED_IO_BUFFER_SIZE ROUND_UP_TO_POW2_CT(sizeof(IOPacket), CACHE_LINE_SIZE)

uint8_t PX4IO_serial_f7::_io_buffer_storage[ALIGNED_IO_BUFFER_SIZE + CACHE_LINE_SIZE];
uint8_t PX4IO_serial_f7::_io_buffer_storage[DMA_ALIGN_UP(sizeof(IOPacket))];

PX4IO_serial_f7::PX4IO_serial_f7() :
_tx_dma(nullptr),
Expand Down Expand Up @@ -119,9 +117,9 @@ int
PX4IO_serial_f7::init()
{
/* initialize base implementation */
int r;
int r = PX4IO_serial::init((IOPacket *)&_io_buffer_storage[0]);

if ((r = PX4IO_serial::init((IOPacket *)ROUND_UP_TO_POW2_CT((uintptr_t)_io_buffer_storage, CACHE_LINE_SIZE))) != 0) {
if (r != 0) {
return r;
}

Expand Down Expand Up @@ -289,7 +287,7 @@ PX4IO_serial_f7::_bus_exchange(IOPacket *_packet)

/* Clean _current_packet, so DMA can see the data */
arch_clean_dcache((uintptr_t)_current_packet,
(uintptr_t)_current_packet + ALIGNED_IO_BUFFER_SIZE);
(uintptr_t)_current_packet + sizeof(_current_packet));

/* start TX DMA - no callback if we also expect a reply */
/* DMA setup time ~3µs */
Expand Down Expand Up @@ -459,7 +457,7 @@ PX4IO_serial_f7::_do_interrupt()
if (_rx_dma_status == _dma_status_waiting) {
/* Invalidate _current_packet, so we get fresh data from RAM */
arch_invalidate_dcache((uintptr_t)_current_packet,
(uintptr_t)_current_packet + ALIGNED_IO_BUFFER_SIZE);
(uintptr_t)_current_packet + sizeof(_current_packet));

/* verify that the received packet is complete */
size_t length = sizeof(*_current_packet) - stm32_dmaresidual(_rx_dma);
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