twi_master_clear_bus fails

[Tom]

Calling twi_master_clear_bus() always returns bus_clear = FALSE. The IF statement is always FALSE even though both SDA and SCL measure high. All 18 SCL's occur in the ELSE but it fails, also. This has worked in the past but recently began failing every time. I tried other previously working firmware versions and they all fail, also. No known events have occurred to cause a hardware failure.

static bool twi_master_clear_bus(void)

{ uint32_t twi_state; bool bus_clear; uint32_t clk_pin_config; uint32_t data_pin_config;

// Save and disable TWI hardware so software can take control over the pins.
twi_state        = NRF_TWI1->ENABLE;
NRF_TWI1->ENABLE = TWI_ENABLE_ENABLE_Disabled << TWI_ENABLE_ENABLE_Pos;

clk_pin_config =
    NRF_GPIO->PIN_CNF[TWI_MASTER_CONFIG_CLOCK_PIN_NUMBER];
NRF_GPIO->PIN_CNF[TWI_MASTER_CONFIG_CLOCK_PIN_NUMBER] =
    (GPIO_PIN_CNF_SENSE_Disabled  << GPIO_PIN_CNF_SENSE_Pos)
  | (GPIO_PIN_CNF_DRIVE_S0D1    << GPIO_PIN_CNF_DRIVE_Pos)    // STD0, DISC1
  | (GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos)
  | (GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos)
  | (GPIO_PIN_CNF_DIR_Output    << GPIO_PIN_CNF_DIR_Pos);

data_pin_config =
    NRF_GPIO->PIN_CNF[TWI_MASTER_CONFIG_DATA_PIN_NUMBER];
NRF_GPIO->PIN_CNF[TWI_MASTER_CONFIG_DATA_PIN_NUMBER] =
    (GPIO_PIN_CNF_SENSE_Disabled  << GPIO_PIN_CNF_SENSE_Pos)
  | (GPIO_PIN_CNF_DRIVE_S0D1    << GPIO_PIN_CNF_DRIVE_Pos)    // STD0, DISC1
  | (GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos)
  | (GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos)
  | (GPIO_PIN_CNF_DIR_Output    << GPIO_PIN_CNF_DIR_Pos);

TWI_SDA_HIGH();
TWI_SCL_HIGH();
TWI_DELAY();

if ((TWI_SDA_READ() == 1) && (TWI_SCL_READ() == 1))
{
    bus_clear = true;
}
else
{
    uint_fast8_t i;
    bus_clear = false;

    // Clock max 18 pulses worst case scenario(9 for master to send the rest of command and 9
    // for slave to respond) to SCL line and wait for SDA come high.
    for (i=18; i--;)
    {
        TWI_SCL_LOW();
        TWI_DELAY();
        TWI_SCL_HIGH();
        TWI_DELAY();

        if (TWI_SDA_READ() == 1)
        {
            bus_clear = true;
            break;
        }
    }
}

NRF_GPIO->PIN_CNF[TWI_MASTER_CONFIG_CLOCK_PIN_NUMBER] = clk_pin_config;
NRF_GPIO->PIN_CNF[TWI_MASTER_CONFIG_DATA_PIN_NUMBER]  = data_pin_config;

NRF_TWI1->ENABLE = twi_state;

return bus_clear;

}

[Tom]

When I said "both SDA and SCL measure high" I meant that when breaking in debug mode just before the if statement both SDA and SCL are high when viewed with a scope. Executing the if statement always skips to the else. I just found that if TWI_SDA_HIGH() and TWI_SCL_HIGH are called in main() both SDA and SCL measure high (scope) just before the if statement. But if these commands are removed the TWI_SDA_HIGH() and TWI_SCL_HIGH() in twi_master_ Does "should work as it should" mean that twi_master_clear_bus() should work without any peripherals tied to SDA and SCL? If this is true does this imply the nrF51822 is bad or might the accelerometer be pulling the bus? The PCB is very small so disconnecting SDA and SCL between the accelerometer and nrF51822 is very difficult.