RE: SPI reading multiple register then concatenate

Meera Shah — Wed, 23 Jan 2019 07:32:58 GMT

What if I want to give a value to the particular register. for an e.g

m_tx_buf[0] = (SPI_READ | LSM6DS3_OUTZ_L_XL );

m_tx_buf[1] = 0x01; //this could be any values then how it will retrieve

RE: SPI reading multiple register then concatenate

StephaneJ — Wed, 06 Dec 2017 21:05:42 GMT

This works very well ;)

RE: SPI reading multiple register then concatenate

StephaneJ — Wed, 06 Dec 2017 20:18:38 GMT

Thanks it seems to work well. I will dig deeper but the first results are encouraging. Thank you very much

RE: SPI reading multiple register then concatenate

Nathan — Wed, 06 Dec 2017 20:09:11 GMT

According to that datasheet your IMU supports multi-byte read operations (end of section 6.2), which auto-increments the address with every byte clocked out. Make m_rx_buf 3 bytes long instead of 2, and modify the rx_length variable used by the nrf_drv_spi_transfer function to be 3. The last two bytes in the buffer are your LSB and MSB. So a simple blocking method you could rewrite for your purpose would be:

uint8_t outz_l_xl;
uint8_t outz_h_xl;
m_tx_buf[0] = (SPI_READ | LSM6DS3_OUTZ_L_XL );
rx_length = 3;
APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, m_tx_buf, 1, m_rx_buf, rx_length));

while (!spi_xfer_done) {}
outz_l_xl = m_rx_buf[1];
outz_h_xl = m_rx_buf[2];

Note however that depending on your specific device this may not be enough (I'm not going through the whole datasheet for you). Some IMUs have an automatic update lock feature so as long as the bus is busy the values won't update. Others do not, in which case they usually have a FIFO you can take advantage of. As long as you don't wait too long to read the values and blow the FIFO's memory limit, each entry in the FIFO is guaranteed to be access safe, and is read using a multi byte access method.