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fix: SPI: remove holes between transfer() #288

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fix: SPI: remove holes between transfer() #288

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91390ac
fix: SPI: remove holes between transfer()
facchinm Dec 10, 2025
95b2b95
SPI: fix: avoid locks with 8/16 bit transfers
pillo79 Dec 18, 2025
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23 changes: 8 additions & 15 deletions libraries/SPI/SPI.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,28 +13,26 @@ arduino::ZephyrSPI::ZephyrSPI(const struct device *spi) : spi_dev(spi) {

uint8_t arduino::ZephyrSPI::transfer(uint8_t data) {
uint8_t rx = data;
if (transfer(&rx, sizeof(rx), &config) < 0) {
if (transfer(&rx, sizeof(rx), SPI_WORD_SET(8)) < 0) {
return 0;
}
return rx;
}

uint16_t arduino::ZephyrSPI::transfer16(uint16_t data) {
uint16_t rx = data;
if (transfer(&rx, sizeof(rx), &config16) < 0) {
if (transfer(&rx, sizeof(rx), SPI_WORD_SET(16)) < 0) {
return 0;
}
return rx;
}

void arduino::ZephyrSPI::transfer(void *buf, size_t count) {
int ret = transfer(buf, count, &config);
int ret = transfer(buf, count, SPI_WORD_SET(8));
(void)ret;
}

int arduino::ZephyrSPI::transfer(void *buf, size_t len, const struct spi_config *config) {
int ret;

int arduino::ZephyrSPI::transfer(void *buf, size_t len, uint32_t flags) {
const struct spi_buf tx_buf = {.buf = buf, .len = len};
const struct spi_buf_set tx_buf_set = {
.buffers = &tx_buf,
Expand All @@ -47,7 +45,8 @@ int arduino::ZephyrSPI::transfer(void *buf, size_t len, const struct spi_config
.count = 1,
};

return spi_transceive(spi_dev, config, &tx_buf_set, &rx_buf_set);
config.operation = mode | flags;
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@iabdalkader iabdalkader Dec 19, 2025

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Suggested change
config.operation = mode | flags;
config.operation = (config.operation & ~SPI_WORD_SIZE_MASK) | flags;

return spi_transceive(spi_dev, &config, &tx_buf_set, &rx_buf_set);
}

void arduino::ZephyrSPI::usingInterrupt(int interruptNumber) {
Expand All @@ -57,7 +56,7 @@ void arduino::ZephyrSPI::notUsingInterrupt(int interruptNumber) {
}

void arduino::ZephyrSPI::beginTransaction(SPISettings settings) {
uint32_t mode = 0;
mode = SPI_HOLD_ON_CS;
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@iabdalkader iabdalkader Dec 19, 2025

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This doesn't really fix the issue as discussed. In any case, it should Never be set unconditionally, what if causes an issue with some random SPI device? This should be added to the API and passed in settings.

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@pennam pennam Dec 19, 2025

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It does not removes the holes, it forces to keep the data and clock line controlled until endTransaction is called.

Releasing data and clock lines causes issues with some SPI sensors libraries.

SPI.transfer(0x2A);
SPI.transfer16(0x010F);

Without SPI_HOLD_ON_CS

GIGA_transfer8_transfer16

With SPI_HOLD_ON_CS

GIGA_transfer8_transfer16_HOLD_CS

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@pennam pennam Dec 19, 2025

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In my opinion SPI_HOLD_ON_CS should be the default way of working, and this is how SPI works with other Arduino cores.

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@iabdalkader iabdalkader Dec 19, 2025 •
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I forgot about endTransaction. Okay then. It's weird though that I don't see CS toggling in the first capture, maybe not enough delay? Also, seems the 16bit transfer is swapped.

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@pennam pennam Dec 19, 2025

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That is not an HW CS is a GPIO. Yes it looks swapped, I've used MSBFIRST flag; let me doublecheck.

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@pennam pennam Dec 19, 2025

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I've used MSBFIRST flag; let me doublecheck.

just ignore this, it changes the bit order so it is unrelated.

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That is not an HW CS is a GPIO.

I know. The GPIO CS delay is also controllable.

Yes it looks swapped

If it matches mbed core, an others, then it's probably fine, I guess.

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See _spi_context_cs_control in spi_context.h.


// Set bus mode
switch (settings.getBusMode()) {
Expand Down Expand Up @@ -93,15 +92,9 @@ void arduino::ZephyrSPI::beginTransaction(SPISettings settings) {
break;
}

// Set SPI configuration structure for 8-bit transfers
// Set SPI configuration structure except for operation
memset(&config, 0, sizeof(struct spi_config));
config.operation = mode | SPI_WORD_SET(8);
config.frequency = max(SPI_MIN_CLOCK_FREQUENCY, settings.getClockFreq());

// Set SPI configuration structure for 16-bit transfers
memset(&config16, 0, sizeof(struct spi_config));
config16.operation = mode | SPI_WORD_SET(16);
config16.frequency = max(SPI_MIN_CLOCK_FREQUENCY, settings.getClockFreq());
}

void arduino::ZephyrSPI::endTransaction(void) {
Expand Down
4 changes: 2 additions & 2 deletions libraries/SPI/SPI.h
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Original file line number Diff line number Diff line change
Expand Up @@ -59,12 +59,12 @@ class ZephyrSPI : public HardwareSPI {
virtual void end();

private:
int transfer(void *buf, size_t len, const struct spi_config *config);
int transfer(void *buf, size_t len, uint32_t flags);

protected:
const struct device *spi_dev;
struct spi_config config;
struct spi_config config16;
uint32_t mode;
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Suggested change
uint32_t mode;

Already stored in operation.

int interrupt[INTERRUPT_COUNT];
size_t interrupt_pos = 0;
};
Expand Down