Using twi vs app_twi

[rookie]

I am trying to set up a humidity sensor over I2C and I'm trying to use the twi interface. There are examples where the app_twi interface is used. I am however unable to get the sensor to respond when using the app_twi interface but can talk to it using the basic twi commands such as nrf_drv_twi_tx. I think the problem might be that the read command implemented as : 

#define MMA7660_READ(p_reg_addr, p_buffer, byte_cnt) \
    APP_TWI_WRITE(MMA7660_ADDR, p_reg_addr, 1,        APP_TWI_NO_STOP), \
    APP_TWI_READ (MMA7660_ADDR, p_buffer,   byte_cnt, 0)

doesn't have a wait between write and read(to account for conversion time and my sensor send a NACK). This is my guess as using the following code makes my sensor work:

        nrf_drv_twi_tx(&m_twi, device_address, dummy_data, sizeof(dummy_data), false);
        nrf_delay_ms(20);

        dummy_data[0] = 0x00;
        nrf_drv_twi_tx(&m_twi, device_address, dummy_data, 1, false);
        nrf_delay_ms(20);

        nrf_drv_twi_rx(&m_twi, device_address, m_sample, sizeof(m_sample));
        nrf_delay_ms(20);

Can you tell me if adding a delay is possible in the macro(if that indeed might be the problem)? How else can I debug this issue in app_twi?

[MartinBL]

Hi,

It could also be that your sensor doesn't handle the no-stop condition (aka repeated start condition between TX and RX) used in your app_twi code. By using your first piece of code there won't be a stop bit between the write and read operation (APP_TWI_NO_STOP). In your second piece of code there will be a stop bit after all transfers (nrf_drv_twi_tx(..,..,..,false)). 

Unfortunately you can't add delays using the app_twi macros. But what happens if you define APP_TWI_NO_STOP to 0 instead of 0x01?

[rookie]

Hi MartinBL,

I tried to change the stop condition to 0x00, but I keep getting a NACK. Not entirely sure what is wrong.

[MartinBL]

Do you have a logic analyzer that yon use to trace what goes on on the TWI bus? It would help if we could actually see what is being clocked out on the bus.

And I can only assume that you are using the samme slave address in both cases?