TWI speed not correct

RE: TWI speed not correct

hmolesworth — Tue, 06 Sep 2022 22:08:36 GMT

Excellent thinking, most helpful and may explain issues we have also seen; I used a different divisor matching that of the uart, but this seems like a better underlying cause. The discussion I had with olfox s here under twi

RE: TWI speed not correct

dbouchie — Tue, 06 Sep 2022 21:46:35 GMT

I've had a similar issue. I think I found the source of the issue: the chip's TWIM clock stretching. I'm unfamilar of how the internal chip circuitry works, but I noticed when I added a longer wire to my circuit, all of a sudden the clock rate went from 250kHZ to 125kHz (with the master frequency set to 250kHz). Just by adding a wire! The additional capacitance must have some effect on the clock stretching circuit.

Just speculating, but the theory would be the slow rise times fool the TWIM into thinking a peripheral is clock stretching, so the TWI skips a clock cycle until the clock line rises back again.

For workarounds, try using a larger pull-up resistor.

RE: TWI speed not correct

T IJ — Wed, 29 Apr 2020 10:59:25 GMT

Sorry for the late response, had some hospital stuff to do.

I've tried the TWI scanner and it resulted in the same speed. 200kbps with 400kbps settings.

I'm using SDK 15.0, I dont know if this makes the difference.

RE: TWI speed not correct

Kenneth — Tue, 28 Apr 2020 08:47:57 GMT

Can you try the SDK example as suggested?

Kenneth

RE: TWI speed not correct

T IJ — Tue, 28 Apr 2020 07:01:36 GMT

This is my code how I use the TWI

    const nrf_twi_config_t twi_config = {.scl = 25,
        .sda = 24,
        .frequency = 0x0c880000, //TWI_FREQUENCY_FREQUENCY_K400,
        .interrupt_priority = 2};

    twi_setup(NRF_TWIM0, &twi_config);


void twi_setup(NRF_TWIM_Type * p_twim, nrf_twi_config_t const * p_config)
{
    NRFX_ASSERT(p_twim);
    NRFX_ASSERT(p_config);
    NRFX_ASSERT(p_config->scl != p_config->sda);
    nrf_twim_disable(p_twim);

    NRF_P0->PIN_CNF[p_config->scl] =
        (GPIO_PIN_CNF_DRIVE_S0D1 << GPIO_PIN_CNF_DRIVE_Pos) & GPIO_PIN_CNF_DRIVE_Msk |
        GPIO_PIN_CNF_PULL_Pullup << GPIO_PIN_CNF_PULL_Pos;
    NRF_P0->PIN_CNF[p_config->sda] =
        (GPIO_PIN_CNF_DRIVE_S0D1 << GPIO_PIN_CNF_DRIVE_Pos) & GPIO_PIN_CNF_DRIVE_Msk |
        GPIO_PIN_CNF_PULL_Pullup << GPIO_PIN_CNF_PULL_Pos;
    NRF_P0->DIRCLR = (1 << p_config->scl) | (1 << p_config->sda);

    nrf_twim_pins_set(p_twim, p_config->scl, p_config->sda);

    nrf_twim_frequency_set(p_twim, p_config->frequency);

    nrf_twim_int_enable(p_twim, NRF_TWIM_INT_STOPPED_MASK | NRF_TWIM_INT_ERROR_MASK);

    NVIC_SetPriority(SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0_IRQn, p_config->interrupt_priority);
    NVIC_EnableIRQ(SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0_IRQn);

    nrf_twim_enable(p_twim);
}

And still I only get 200kbps if I use the TWI_FREQUENCY_FREQUENCY_K400 macro.

I dont know if I done something odd in my code or not.

RE: TWI speed not correct

Kenneth — Mon, 27 Apr 2020 13:08:02 GMT

I compiled the twi scanner example:
\nRF5_SDK_15.3.0_59ac345\examples\peripheral\twi_scanner

Then modified twi_init():

void twi_init (void)
{
    ret_code_t err_code;

    const nrf_drv_twi_config_t twi_config = {
       .scl                = ARDUINO_SCL_PIN,
       .sda                = ARDUINO_SDA_PIN,
       .frequency          = NRF_DRV_TWI_FREQ_400K,
       .interrupt_priority = APP_IRQ_PRIORITY_HIGH,
       .clear_bus_init     = false
    };

    err_code = nrf_drv_twi_init(&m_twi, &twi_config, NULL, NULL);
    APP_ERROR_CHECK(err_code);

    nrf_gpio_cfg_input(ARDUINO_SCL_PIN, NRF_GPIO_PIN_PULLUP);
    nrf_gpio_cfg_input(ARDUINO_SDA_PIN, NRF_GPIO_PIN_PULLUP);

    nrf_drv_twi_enable(&m_twi);
}

RE: TWI speed not correct

T IJ — Thu, 23 Apr 2020 11:08:58 GMT

The value I read back is set to 6.

RE: TWI speed not correct

Kenneth — Thu, 23 Apr 2020 11:00:17 GMT

If you read out the NRF_TWI->ENABLE register, what is the value here?

Best regards,
Kenneth

RE: TWI speed not correct

T IJ — Thu, 23 Apr 2020 08:38:25 GMT

Ive gotten myself a second nRF52832 development kit to test it on and this one does the same as the other development kit.

When I set the TWI speed to TWI_FREQUENCY_FREQUENCY_K400 it only sends out a 200kHz clock instead of the 400kHz clock I'd expect.
Only when I set the frequency register to something else than is listed in the datasheet or in nrf52_bitfields.h I am able to get 400kHz or higher even.

Has anyone experienced this as well?

RE: TWI speed not correct

T IJ — Wed, 22 Apr 2020 10:07:47 GMT

But the speed listed in the datasheet at 400kbps is not correct, I get 200kbps of speed.

const nrf_twi_config_t twi_config = 
{
    .scl = 25,
    .sda = 24,
    .frequency = TWI_FREQUENCY_FREQUENCY_K400,
    .interrupt_priority = 2
};

twi_setup(NRF_TWIM0, &twi_config);

This results in 200kbps.

If I change .frequency to 0x0C880000 I get 400kbps, so how is this qualified if it doesntt result in the proper frequency whilst the other frequency settings result in the intended frequency.

RE: TWI speed not correct

Kenneth — Wed, 22 Apr 2020 09:58:32 GMT

It's only the frequencies listed in the datasheet that has been tested and qualified, so I recommend to use those.

For TWIM (TWI with EasyDMA) that is:
https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.nrf52832.ps.v1.1%2Ftwim.html&anchor=register.FREQUENCY

For TWI (legacy TWI inherit from older nRF51-series):
https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.nrf52832.ps.v1.1%2Ftwi.html&anchor=register.FREQUENCY

It is the ENABLE register that choose whether TWIM or TWI is used, and thereby also the configuration of the registers. If you use TWIM have this errata in mind that indirectly regards frequency:
https://infocenter.nordicsemi.com/topic/errata_nRF52832_Rev2/ERR/nRF52832/Rev2/latest/anomaly_832_219.html

Best regards,
Kenneth