TWI Switch between easyDMA and normal read

[Constantin]

Hi,

I am reading a BMX055 via I2C which consists of three sensors with three addresses. I got the easyDMA running to read 10 times the gyro using the PPI and the data ready interrupt. Now after 10 readings I want to read once the accelerometer and the magnetometer. But if I try to read with

nrf_drv_twi_tx(&m_twi_instance, address, &reg, 1, false); nrf_drv_twi_rx(&m_twi_instance, address, p_data, length);

I get the NRF_ERROR_BUSY which means that the TWIM is still in use. So here is my question how can I switch from easyDMA reading to normal reading.

Thanks and kind regards,

C.

[Constantin]

No it is the following problem: I start a easydma transfer for 10 gyro samples with:

// Disable the TWIM module while we reconfigure it
NRF_TWIM0->ENABLE = TWIM_ENABLE_ENABLE_Disabled << TWIM_ENABLE_ENABLE_Pos;
NRF_TWIM0->SHORTS = 0;
NVIC_DisableIRQ(SPI0_TWI0_IRQn);
NVIC_ClearPendingIRQ(SPI0_TWI0_IRQn);

// Configure a gpiote channel to generate an event on a polarity change from
// low to high generated the BMX interrupt pin.
uint8_t gpiote_ch_bmx_int_event = 0;
NRF_GPIOTE->CONFIG[gpiote_ch_bmx_int_event] = ( (GPIOTE_CONFIG_MODE_Event   << GPIOTE_CONFIG_MODE_Pos) |
                                                (BMX_INT_PIN                << GPIOTE_CONFIG_PSEL_Pos) |
                                                (GPIOTE_CONFIG_POLARITY_LoToHi << GPIOTE_CONFIG_POLARITY_Pos));

NRF_TWIM0->PSEL.SCL = BMX_TWI_SCL_PIN;
NRF_TWIM0->PSEL.SDA = BMX_TWI_SDA_PIN;
NRF_TWIM0->FREQUENCY = TWI_FREQUENCY_FREQUENCY_K400;

// Load TWI TX buffer into TWI module. Set number of bytes to write pr transfer, max count, to one.
// Disable the EasyDMA list functionality for TWI TX.
NRF_TWIM0->TXD.PTR = (uint32_t)&p_tx_gyro_buffer;
NRF_TWIM0->TXD.MAXCNT = 1;
NRF_TWIM0->TXD.LIST = TWIM_TXD_LIST_LIST_Disabled << TWIM_TXD_LIST_LIST_Pos;

// Point to TWI RX buffer. Set number of bytes to read pr transfer, max count, to TWIM_RX_BUF_WIDTH.
// Disable the EasyDMA list functionality for TWI TX
NRF_TWIM0->RXD.PTR = (uint32_t)&p_rx_gyro_buffer;
NRF_TWIM0->RXD.MAXCNT = TWIM_RX_BUF_WIDTH_GYRO_ONLY;
NRF_TWIM0->RXD.LIST = TWIM_RXD_LIST_LIST_ArrayList << TWIM_RXD_LIST_LIST_Pos;

// Make sure that BMX address is set
NRF_TWIM0->ADDRESS = BMX055_GYRO_ADDRESS;
// Enable shortcuts that starts a read right after a write and sends a stop condition after last TWI read
NRF_TWIM0->SHORTS = (TWIM_SHORTS_LASTTX_STARTRX_Enabled << TWIM_SHORTS_LASTTX_STARTRX_Pos) |
                    (TWIM_SHORTS_LASTRX_STOP_Enabled << TWIM_SHORTS_LASTRX_STOP_Pos);

// Configure PPI channel
// Use BMX interrupt pin as event
// Start timer 0 on event to count number of transfers
// Also start TWI transfers on event
// Enable PPI channel
NRF_PPI->CH[0].EEP = (uint32_t)&NRF_GPIOTE->EVENTS_IN[gpiote_ch_bmx_int_event];
NRF_PPI->CH[0].TEP = (uint32_t)&NRF_TIMER0->TASKS_COUNT;
NRF_PPI->FORK[0].TEP = (uint32_t)&NRF_TWIM0->TASKS_STARTTX;

// Enable the TWIM module
NRF_TWIM0->ENABLE = TWIM_ENABLE_ENABLE_Enabled << TWIM_ENABLE_ENABLE_Pos;

then when I get the interrupt of the timer I do the following:

// Clear timer event
NRF_TIMER0->EVENTS_COMPARE[0] = 0;
// Reset the TWIM RX pointer to initial address of RX buffer
NRF_TWIM0->RXD.PTR = (uint32_t)&p_rx_gyro_buffer;
// Toggle a LED for show
nrf_gpio_pin_toggle(LED_1);
// Set flag to notify main context of the new data available
twi_gyro_transfers_complete = true;

Now I want at the same interrupt read the accelerometer and magnetometer only once and then return with the gyro reading. But if I try either reading or writing during the interrupt routine or in the main after reading the flag I get NRF_ERROR_BUSY.