How do I write a value V to a register R using device address A with nrf_drv_twi ?

Question

I am using nrf51822, sdk version 11.0, sofdevice 130, i2c initialized in non-blocking mode. The read seems ok. The write is problematic for me.

Josh Grob · Answer

I think Jorgen points to the best answer. For completeness below are some helper functions I have used to do write/read operations for the nrf twi interface. 
 //write byte to register
void write_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address, uint8_t *data, bool stop)
 { 
 ret_code_t err_code;
 uint8_t data_write[2];
 
 data_write[0] = sub_address;
 data_write[1] = *data;
 
 err_code = nrf_drv_twi_tx(twi_handle, address, data_write, sizeof(data_write), stop); 
 APP_ERROR_CHECK(err_code);
 }

//reading byte or bytes from register 
void write_forread_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address)
 { 
 ret_code_t err_code;
 
 err_code = nrf_drv_twi_tx(twi_handle, address, &sub_address, sizeof(sub_address), true); 
 APP_ERROR_CHECK(err_code);
 }
 
 char read_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address)
 { 
 ret_code_t err_code;
 uint8_t data; // `data` will store the register data 
 
 write_forread_byte(twi_handle, address, sub_address);
 
 err_code = nrf_drv_twi_rx(twi_handle, address, &data, sizeof(data));
 APP_ERROR_CHECK(err_code);
 
 return data; 
 }
 
 void read_bytes(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address, uint8_t * dest, uint8_t dest_count)
 { 
 ret_code_t err_code; 
 
 write_forread_byte(twi_handle, address, sub_address);
 
 err_code = nrf_drv_twi_rx(twi_handle, address, dest, dest_count);
 APP_ERROR_CHECK(err_code);
 }

How do I write a value V to a register R using device address A with nrf_drv_twi ?

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