nRF24L01+ raises IRQ on PRX side only once

RE: nRF24L01+ raises IRQ on PRX side only once

Ralph Krüger — Sun, 28 Dec 2014 17:21:35 GMT

I'm not absolutely sure (because there MAY be other changes done during a somewhat longer development cycle), but most probably this solved the problem. Strange though, since this is not what someone would expect after having read the manual.

RE: nRF24L01+ raises IRQ on PRX side only once

Derek Goslin — Fri, 21 Nov 2014 09:36:57 GMT

Hi,

I have experienced the same issue possibly caused for the same reason hopefully this can save someone else time and sanity.

I paired the problem back to a simple test case.

Configure the TX and the RX with all default initialized values, i.e. PWR_UP = 1 and set CE = 1 and PRIM_RX = 0 on TX. Optionally you can enable Dynamic Payload Length and W_TX_PAYLOAD_NOACK command.

When the TX sends a packet with or without ACK the RX will see the initial RX_DR interrupt.

In my interrupt handler I was first reading and "clearing" via write of a 1 to the STATUS register bits

uint8_t hal_nrf_get_clear_irq_flags(void)
{
  return hal_nrf_write_reg(STATUS, (BIT_6|BIT_5|BIT_4)) & (BIT_6|BIT_5|BIT_4);
}

Then I was using the return value to determine the source of the interrupt. And handling it as follows:

while (!hal_nrf_rx_fifo_empty())
{
	hal_nrf_read_rx_pload(pload);
}

radio_set_status (RF_RX_DR);

The handler reads the payload into a buffer called pload and then sets a status flag when not more packets are in the RX fifo.

NOTE: The astute will notice that this code can cause dropped packets. For the packet rate that I am using this is adequate. For higher speed rates this code fails.

My MCU is basically in a sleep state awaiting an external interrupt. The interrupt from the NRF24L01P device wakes the MCU up and execution continues. In the MCUs code path post wake up I was doing the following:

radio_status_t status = radio_get_status();
			
if(status == RF_RX_DR)
{
	uint16_t packet_info = hal_nrf_read_rx_pload((uint8_t *) &packet);

The hal_nrf_read_rx_pload methods is defined as the following:

uint16_t hal_nrf_read_rx_pload(uint8_t *rx_pload)
{
  return hal_nrf_read_multibyte_reg(UINT8(HAL_NRF_RX_PLOAD), rx_pload);
}

The hal_nrf_read_multibyte_reg method executes the R_RX_PL_WID command to get the payload length and then reads the payload via the R_RX_PAYLOAD command.

It is this sequence of reads that seems to put the NRF24L01P into a strange state whereby the TX gets an ACK but no interrupt occurs.

Another behavior that I observed was that the TX will get an ACK for the first three packets and then transmission fails due to MAX_RT. This makes sense in light of the above as the RX is not clearing its FIFO because there are not interrupts being fired to the MCU to read the packet data.

To resolve the problem I simply stopped reading from the receive payload registers, which was the source of this bug, and read from the payload buffer instead. Alternately I could have modified the interrupt code to simply set the status and allowed the MCU main like code to read the receive registers.

Regards Derek

RE: nRF24L01+ raises IRQ on PRX side only once

Håkon Alseth — Wed, 26 Mar 2014 11:20:21 GMT

Hi,

You should enable the PIPEs that you're using in registers RX_PW_Px on both sides. If these are set to '0' the pipe is not used. For the PTX it's usually only RX_PW_P0.

Best regards Håkon

RE: nRF24L01+ raises IRQ on PRX side only once

Ralph Krüger — Tue, 25 Mar 2014 15:57:14 GMT

Yes Håkon, both conditions/procedures you named are fulfilled.

What amazes me is the fact, that exactely this kind of communication already worked in another project (based on another architecture).

And, as far as I can see, the inner state of the nRF24L01+ (i.e. its register contents) as well as its outer state (signal lines, namely CE) are identical when receiving the first message from the PTX and any following message. But nevertheless, there MUST be a difference anywhere...

I am totally clueless :/

Any further guesses/hints?

Best regards Ralph

In case you want to check for yourself:

The PTX registers are:

****** nRF24L01+ register set ****** Register 0x00 = 0x0E Register 0x01 = 0x3F Register 0x02 = 0x01 Register 0x03 = 0x01 Register 0x04 = 0x2F Register 0x05 = 0x00 Register 0x06 = 0x26 Register 0x07 = 0x0E Register 0x08 = 0x00 Register 0x09 = 0x00 Register 0x0A = 0x01, 0x01, 0x42, 0xE7, 0xE7 Register 0x0B = 0xFF, 0xFF, 0x42, 0xC2, 0xC2 Register 0x0C = 0xFF Register 0x0D = 0xFF Register 0x0E = 0xFF Register 0x0F = 0xFF Register 0x10 = 0x01, 0x01, 0x42, 0xE7, 0xE7 Register 0x11 = 0x00 Register 0x12 = 0x00 Register 0x13 = 0x00 Register 0x14 = 0x00 Register 0x15 = 0x00 Register 0x16 = 0x00 Register 0x17 = 0x11 Register 0x1C = 0x3F Register 0x1D = 0x07

I use only 3 address bytes, so (0x01, 0x01, 0x42) is the relevant part.

RE: nRF24L01+ raises IRQ on PRX side only once

Håkon Alseth — Tue, 25 Mar 2014 13:57:50 GMT

Hi,

On the PTX side, are you setting "TX_ADDR" register equal to "RX_PW_P0"? If not, the auto-acking will not work properly.
How are you clearing the STATUS (0x07) register? You should read the content, then write '1' to the bits to clear it; statusval = read_reg(STATUS); retval = write_reg(STATUS, statusval);

Best regards Håkon