SPI AND SPIM READING ISSUES

Question

hi all i am trying to read data from a sensor in burst mode i can"t able to read all datas from the register .I tried to read the data in both spi and spim(with easydma) . spim is more better it reads data from 2 register(i am trying to read data of 3 register using burst mode).how can i solve this issues.

hmolesworth · Accepted Answer

This is the problem, I think: 
 spi_config.ss_pin = SPI_MOUSE_CSN_PIN; 
 This causes the SPIM driver to de-activate NCS between the first byte and the next 3 bytes, which terminates the burst transfer. Change this to manually drive NCS low before and after the transfers, not between. 
 From the data sheet " After sending the register address, the microcontroller must wait tSRAD and then begin reading data. All data bits can be read with no delay between bytes by driving SCLK at the normal rate. " tSRAD is 4uSecs, so for the "burst" read you are using the first byte is sent without removing NCS the three bytes are read in in the next SPI transfer, So send two commands and do not allow the spim handler to drive NCS and ensure there is at least 4 usec delay between 1st and second commands.

hmolesworth · Answer

I assume you control NCS correctly, setting low before the first of two transfers and only high after the second with the 4 uSec delay between the two transfers. However your code shows that you are also telling the nRF SPI code to take control of NCS. Here is the default setting for NCS and the handler for init: 
 // Starts by assuming NCS is not required

/**
 * @brief SPI master instance default configuration.
 */
#define NRF_DRV_SPI_DEFAULT_CONFIG \
{ \
 .sck_pin = NRF_DRV_SPI_PIN_NOT_USED, \
 .mosi_pin = NRF_DRV_SPI_PIN_NOT_USED, \
 .miso_pin = NRF_DRV_SPI_PIN_NOT_USED, \
 .ss_pin = NRF_DRV_SPI_PIN_NOT_USED, \
 .irq_priority = SPI_DEFAULT_CONFIG_IRQ_PRIORITY, \
 .orc = 0xFF, \
 .frequency = NRF_DRV_SPI_FREQ_4M, \
 .mode = NRF_DRV_SPI_MODE_0, \
 .bit_order = NRF_DRV_SPI_BIT_ORDER_MSB_FIRST, \
}

// Tests if NCS is not required

 // - Slave Select (optional) - output with initial value 1 (inactive).
 if (p_config->ss_pin != NRF_DRV_SPI_PIN_NOT_USED)
 {
 nrf_gpio_pin_set(p_config->ss_pin);
 nrf_gpio_cfg_output(p_config->ss_pin);
 }
 m_cb[p_instance->drv_inst_idx].ss_pin = p_config->ss_pin;

 
 However your code shows that you are requesting the nRF SPI driver to take over NCS: 
 spi_config.ss_pin = SPI_MOUSE_CSN_PIN; 
 The nRF handler will now drive NCS low before and high after every transaction, including between the two transactions you require, for example sww nrf_drv_spi.c 
 static void finish_transfer(spi_control_block_t * p_cb)
{
 // If Slave Select signal is used, this is the time to deactivate it.
 if (p_cb->ss_pin != NRF_DRV_SPI_PIN_NOT_USED)
 {
 nrf_gpio_pin_set(p_cb->ss_pin);
 }

SPI AND SPIM READING ISSUES

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