After I write to the FIFO, I read the FIFO to check if the bytes were property transferred (I understand that I cannot read and then transmit, this is just for debugging). I have a strange issue where the number of bytes in the FIFO are exactly half of what I write. Also, the bytes themselves are not what I wrote. Each time I read from the FIFO, the number of bytes in the FIFO are halved until there are zero bytes.
Here I write to the FIFO:
HAL_GPIO_WritePin(SPI_SS_GPIO_Port, SPI_SS_Pin, GPIO_PIN_RESET);
ret = HAL_SPI_Transmit(&hspi2, &FIFO_w, 1, 50);
ret = HAL_SPI_Transmit(&hspi2, &sof, 1, 50);
ret = HAL_SPI_Transmit(&hspi2, ppm_message, ppm_message_len, 50);
ret = HAL_SPI_Transmit(&hspi2, &eof, 1, 50);
HAL_GPIO_WritePin(SPI_SS_GPIO_Port, SPI_SS_Pin, GPIO_PIN_SET);
And here I read the FIFO length and FIFO itself:
HAL_GPIO_WritePin(SPI_SS_GPIO_Port, SPI_SS_Pin, GPIO_PIN_RESET);
ret = HAL_SPI_Transmit(&hspi2, &FIFO_status_addr_r, 1, 50);
ret = HAL_SPI_Receive(&hspi2, &raw_rx_len, 1, 50);
HAL_GPIO_WritePin(SPI_SS_GPIO_Port, SPI_SS_Pin, GPIO_PIN_SET);
uint8_t raw_rx[raw_rx_len];
HAL_GPIO_WritePin(SPI_SS_GPIO_Port, SPI_SS_Pin, GPIO_PIN_RESET);
ret = HAL_SPI_Transmit(&hspi2, &FIFO_r, 1, 50);
ret = HAL_SPI_Receive(&hspi2, raw_rx, raw_rx_len, 50);
HAL_GPIO_WritePin(SPI_SS_GPIO_Port, SPI_SS_Pin, GPIO_PIN_SET);
ppm_message[24] is: {0x20, 0x02, 0x02, 0x02, 0x08, 0x80...}
raw_rx[12] is: {0x10, 0x90, 0x01, 0x01, 0x01, 0x04, 0x40...}
the next FIFO read produces:
raw_rx[6] is: {0x01, 0x01, 0x01, 0x01, 0x04, 0x40}
and then:
raw_rx[3] is: {0x40, 0x40, 0x40}
and so on...
Its strange that the raw_rx looks vaguely like the ppm_message in terms of the pattern of repeated numbers.
Any help or guesses would be greatly appreciated!
Thanks,
Oliver
