How to stop nRF52832 I2C clock?

[snowuyl]

I would like to stop nRF52832 I2C clock for power saving. Which API should I use?

[snowuyl]

Fullscreen 5430.i2c.c Download

#include <string.h>
#include "i2c.h"
#include "app_error.h"
#include "app_util_platform.h"
#include "bsp.h"
#include "error.h"
#include "nrf.h"
#include "nrf_delay.h"
#include "nrf_drv_twi.h"
#include "nrf_log.h"

static uint8_t slave_addr;
static const nrf_drv_twi_t m_twi_master = NRF_DRV_TWI_INSTANCE(1);

int I2C_Init(void) {
	ret_code_t ret;
	const nrf_drv_twi_config_t config =
	{
		.scl                = TWI_SCL_M,
		.sda                = TWI_SDA_M,
		.frequency          = (nrf_drv_twi_frequency_t) NRF_TWI_FREQ_400K,
		.interrupt_priority = APP_IRQ_PRIORITY_HIGH
	};

    ret = nrf_drv_twi_init(&m_twi_master, &config, NULL, NULL);
	if (NRF_SUCCESS != ret) {
	    NRF_LOG_WARNING("");
        return ERROR_I2C_INITIALIZE_FAIL;
	}
    
	nrf_drv_twi_enable(&m_twi_master);

	return 0;
}

void I2C_Uninit(void) {
	nrf_drv_twi_uninit(&m_twi_master);
}

void I2C_SlaveAddr(uint8_t addr) {
	slave_addr = addr;
}

ret_code_t I2C_WriteReg(uint8_t reg, uint8_t data) {
	static ret_code_t ret;
	uint8_t buff[2];
	
	buff[0] = reg;
	buff[1] = data;
	
	ret = nrf_drv_twi_tx(&m_twi_master, slave_addr, buff, sizeof(buff), false);
	
	return ret;
}

ret_code_t I2C_WriteData(uint8_t reg,uint8_t *data,int len) {
	static ret_code_t ret;
	uint8_t buff[256];

	buff[0] = reg;
	memcpy(&buff[1],data,len);
	
	ret = nrf_drv_twi_tx(&m_twi_master, slave_addr, buff, len+1, false);
	
	return ret;
}


ret_code_t I2C_ReadBatchData(uint8_t reg,uint8_t *data,int len) {
	static ret_code_t ret;
	
	ret = nrf_drv_twi_tx(&m_twi_master, slave_addr, &reg, 1, true);
	if(NRF_SUCCESS != ret)
		return ret;
	
	ret = nrf_drv_twi_rx(&m_twi_master, slave_addr, data,len);
	
	return ret;
}

ret_code_t I2C_ReadData(uint8_t reg,uint8_t *data,int len) {
	static ret_code_t ret;
	
	ret = nrf_drv_twi_tx(&m_twi_master, slave_addr, &reg, 1, true);
	if(NRF_SUCCESS != ret)
		return ret;
	
	ret = nrf_drv_twi_rx(&m_twi_master, slave_addr, data,len);
	
	return ret;
}

uint8_t I2C_ReadReg(uint8_t reg) {
	static ret_code_t ret;
	uint8_t data = 0xFD;
	
	ret = nrf_drv_twi_tx(&m_twi_master, slave_addr, &reg, 1, true);
	if(NRF_SUCCESS != ret)
		return data;
	ret = nrf_drv_twi_rx(&m_twi_master, slave_addr, &data,1);
	
	return data;
}

[Jared]

Hi,

Un- initializing the driver after the transaction has stopped should be enough.

In some cases, the TWI driver will not stop the clock even after un-initializing the driver. If that is the case, then you're most likely experiencing errata 89, you should then power cycle the peripheral by following the workaround as described here.

regards
Jared 

[snowuyl]

Thanks for your reply! I use I2C as communication interface between nRF52832 and analog front-end (AFE). I have power down AFE. Do I need to uninitialize  I2C driver for stopping I2C clock for power saving?

[Jared]

The clock should be stopped after the transaction has stopped. It would be best to un-initialize  the TWI driver after you're done with the transaction to save as much power as possible. How are you determining the state of the clock? Are you measuring the power consumption?

[snowuyl]

After calling I2c uninitialized function, i2c in high or low state? Do I need to call gpio function to force it to high or low state?

[Jared]

Hi,

The GPIOs assigned to SDA and SCL will be configured back to its default state as Input with Input buffer disconnected and no pull. 

regards
Jared