nRF52832 SPI function

RE: nRF52832 SPI function

rohit — Mon, 01 Oct 2018 09:04:19 GMT

Hello Jan,

I am also trying same

Is it working Reg_read and Reg_write function for SPI Communication?

please let me know

thanks and regards,

rohit

RE: nRF52832 SPI function

hmolesworth — Wed, 11 Apr 2018 18:35:21 GMT

Technically you would write &mTxBuf[0] to correctly form the exact same pointer as mTxBuf; often something like &mTxBuf[strlen(mTxBuf)] is used to obtain a pointer to the location where one would append text to a string, assuming an ascii string of course as that has the \0 terminator which strlen() requires to identify the end-of-string. Note &mTxSomething where mTxSomething is a single character cannot be used as a string pointer, just a pointer to a single character. If that is passed to a function which requires a pointer to data the system would die a horrible death unless the length was set to 1.

RE: nRF52832 SPI function

Jan Lundskov — Wed, 11 Apr 2018 16:40:50 GMT

Thanks for your reply. It works now when I change the m_tx_buf and m_rx_buf arguments to pointers. So just to make sure that I understand it correctly...

Since mTxBuf[] and mRxBuf[] in your example above are both defined as arrays, then simply writing 'mTxBuf' and 'mRxBuf' is the same as writing &mTxBuf and &mRxBuf if they were only defined as simple uint8_t (not an array of uint8_t). Is that correctly understood?

RE: nRF52832 SPI function

hmolesworth — Wed, 11 Apr 2018 15:37:11 GMT

There is a bug in the code you list above, but due to the way the c compiler works you can fool the code into working. Look at the definition of nrf_drv_spi_transfer(), it requires pointers to the buffers

ret_code_t nrf_drv_spi_transfer(nrf_drv_spi_t const * const p_instance,
                                uint8_t const * p_tx_buffer,
                                uint8_t         tx_buffer_length,
                                uint8_t       * p_rx_buffer,
                                uint8_t         rx_buffer_length)

The buffers mTxBuf[] and mRxBuf[] are pointers as they are defined as arrays, and are used as pointers by nrf_drv_spi_transfer():

uint8_t mTxBuf[] = {ADS_CMND_RREG, NUMBER_OF_ADS_REGISTERS-1, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
uint8_t mRxBuf[sizeof(mTxBuf)];

APP_ERROR_CHECK(nrf_drv_spi_transfer(&mAfeSpiInstance, mTxBuf, mRxTxBufLength, mRxBuf, mRxTxBufLength));

Your function definition omits the pointer definition, and so expects uint8_t values, which in practice probably passes as 32-bit values which you have been able to force to pointers (also 32-bit values)

void ReadWriteSPI(nrf_drv_spi_t spi, uint8_t m_tx_buf, uint8_t m_rx_buf, uint8_t m_length)

Change function definition to use pointers to correct this issue:

void ReadWriteSPI(nrf_drv_spi_t spi, uint8_t *m_tx_buf, uint8_t *m_rx_buf, uint8_t m_length)

RE: nRF52832 SPI function

Jan Lundskov — Wed, 11 Apr 2018 10:44:07 GMT

Hi,

I have just found that if I add the pointer operator '&' in front of m_tx_buf and m_rx_buf, then it seems to work. But why is that not necessary in the sample code..?

So this seems to work

APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, &m_tx_buf, m_length, &m_rx_buf, m_length));

Regards,

Jan