nRF52 receive advertisement with raw register access

Question

Hi,

I am trying to receive BLE advertisements on Ch38 (=2426MHz) without using SoftDevice, i.e. with direct register access.
However "EVENTS_DISABLED" is very rarely called (if at all). Any ideas what I might be doing wrong?

	NRF_RADIO->SHORTS       = (1 << RADIO_SHORTS_READY_START_Pos) |  // Shortcut between READY event and START task
                              (1 << RADIO_SHORTS_END_DISABLE_Pos);   // Shortcut between END event and DISABLE task	NRF_RADIO->MODECNF0 = (RADIO_MODECNF0_RU_Fast << RADIO_MODECNF0_RU_Pos);
	NRF_RADIO->FREQUENCY =  26;
	NRF_RADIO->MODE = (RADIO_MODE_MODE_Ble_1Mbit << RADIO_MODE_MODE_Pos);
	NRF_RADIO->DATAWHITEIV = 38;
		
	uint32_t m_address = 0x8E89BED6;
	
	NRF_RADIO->PREFIX0     = 0;
	NRF_RADIO->PREFIX0    &= ~RADIO_PREFIX0_AP0_Msk;
    NRF_RADIO->PREFIX0    |= (m_address >> 24) & RADIO_PREFIX0_AP0_Msk;
    NRF_RADIO->BASE0       = m_address << 8;
    NRF_RADIO->RXADDRESSES = RADIO_RXADDRESSES_ADDR0_Enabled << RADIO_RXADDRESSES_ADDR0_Pos;
    NRF_RADIO->TXADDRESS   = (0x00 << RADIO_TXADDRESS_TXADDRESS_Pos) & RADIO_TXADDRESS_TXADDRESS_Msk;

	
	NRF_RADIO->EVENTS_DISABLED = 0;
	NRF_RADIO->EVENTS_END = 0;
	NRF_RADIO->EVENTS_READY = 0;
	NRF_RADIO->TASKS_RXEN = 1;	
	while (!NRF_RADIO->EVENTS_DISABLED ); // gets stuck
	NRF_RADIO->EVENTS_DISABLED = 0;

Best,
Paul

ovrebekk · Answer

Hi Paul 
 Your code seems fine, but perhaps you didn't start the external 32MHz crystal? 
 Without this running the radio will be running off of the internal RC oscillator, which means the frequency will be way off and the reception poor. 
 If you start the external clock before enabling the radio the code should work fine: 
 NRF_CLOCK->EVENTS_HFCLKSTARTED = 0; NRF_CLOCK->TASKS_HFCLKSTART = 1; while(NRF_CLOCK->EVENTS_HFCLKSTARTED == 0); 
 For future reference you can also have a look at the radio HAL from the solar beacon example. This example is sending advertise packets rather than receiving them, but the radio configuration is very similar for TX and RX: https://github.com/NordicPlayground/solar_sensor_beacon/blob/master/src/hal_radio.c 
 Best regards Torbjørn

nRF52 receive advertisement with raw register access

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