In document, there is a remark to highlight each write (or read) transfer is limited to 4096 bytes.
https://docs.microsoft.com/en-us/azure-sphere/reference/applibs-reference/applibs-spi/function-spimaster-transfersequential
What I'm trying to do is split my large data blocks into multiple transfers. I wrote below code and did some debug. When I have two transfer descriptor, e.g. the first one is 4096, then second one is 8, I will get a invalid augment error.
Is this API limited to 4096 bytes in maximum or applied to each transfer descriptor?
My code:
#define MAX_SPI_TRANSFER_BYTES 4096
int ll_spi_rx(uint8_t *rx_data, uint32_t rx_len)
{
size_t numOfXfer = (rx_len % MAX_SPI_TRANSFER_BYTES == 0) ? (rx_len / MAX_SPI_TRANSFER_BYTES) : (rx_len / MAX_SPI_TRANSFER_BYTES + 1);
SPIMaster_Transfer *p_transfer_array = malloc(sizeof(SPIMaster_Transfer) * numOfXfer);
int ret = SPIMaster_InitTransfers(p_transfer_array, numOfXfer);
if (ret < 0) {
Log_Debug("ERROR: SPIMaster_InitTransfers: errno=%d (%s)\n", errno, strerror(errno));
free(p_transfer_array);
return -1;
}
int32_t offset = 0;
int32_t sizeleft = rx_len;
for (uint32_t i = 0; i < numOfXfer; i++) {
p_transfer_array[i].flags = SPI_TransferFlags_Read;
p_transfer_array[i].readData = rx_data + offset;
p_transfer_array[i].length = sizeleft > MAX_SPI_TRANSFER_BYTES ? MAX_SPI_TRANSFER_BYTES : sizeleft;
sizeleft -= MAX_SPI_TRANSFER_BYTES;
offset += MAX_SPI_TRANSFER_BYTES;
}
ret = SPIMaster_TransferSequential(spiFd, p_transfer_array, numOfXfer);
if (ret < 0) {
Log_Debug("ERROR: SPIMaster_TransferSequential: errno=%d (%s)\n", errno, strerror(errno));
free(p_transfer_array);
return -1;
} else if (ret != rx_len) {
Log_Debug("ERROR: SPIMaster_TransferSequential transfer %d bytes, expect %d bytes\n", ret, rx_len);
free(p_transfer_array);
return -1;
}
free(p_transfer_array);
return 0;
}
