1.4 SerialGateway freezes

[Yveaux]

@hek Looked it up in the datasheet:

If the TX FIFO (PRX) contains more than one payload to a PTX, payloads are handled using the first in –
first out principle. The TX FIFO (PRX) is blocked if all pending payloads are addressed to a PTX where the
link is lost. In this case, the MCU can flush the TX FIFO (PRX) by using the FLUSH_TX command.
.....
While executing the Auto Retransmit feature, the number of retransmits can reach the maximum number
defined in ARC. If this happens, the nRF24L01+ asserts the MAX_RT IRQ and returns to standby-I mode.
.....
MAX_RT IRQ is asserted if the auto retransmit counter (ARC_CNT) exceeds the programmed maximum limit
(ARC). In Figure 24. the packet transmission ends with a MAX_RT IRQ. The payload in TX FIFO is NOT
removed and the MCU decides the next step in the protocol. A toggle of the CE starts a new transmitting
sequence of the same packet. The payload can be removed from the TX FIFO using the FLUSH_TX command.

The FIFO is 3 entries big, so 3 successive failed transmissions to the same destination will block the transmission.
This FIFO needs to be flushed after a failed transmission (indicated by the MAX_RT IRQ) by executing the FLUSH_TX command.
Add the following method to the NRF24 class:

uint8_t RF24::flush_tx(void)
{
  return spiTrans( FLUSH_TX );
}

and when you're at it, please also add (used e.g. by the sniffer):

uint8_t RF24::flush_rx(void)
{
  return spiTrans( FLUSH_RX );
}

This might very well be a very nasted bug bugging the 1.4 users...

[hek]

@Yveaux

Ohh.. interesting.

So are you saying we should flush_tx after every failed send? Or only after 3 consecutive send-fails to the same address?

[Yveaux]

@hek after every failed send.

[hek]

@Yveaux

Can you make some tests perhaps? And create a pull req with the changes in RF24 and MySensor.cpp if you see any improvements?

[Yveaux]

@hek will take some time but I'll see what I can do. I'll get back with some data.

[hek]

@Yveaux

Take your time. We don't have any deadlines or bosses hanging over the shoulder here :smile:

[Yveaux]

@hek true, but I have a gut feeling some troubles reported on this forum lately could be related to this. Furthermore I've seen strange repeated messages on air, but didn't investigate yet...

[hek]

@Yveaux

One shouldn't underestimate a gut feeling. They are often proven to be right.

[Yveaux]

@hek Ok, gut feeling was wrong this time ;-)
Buried deep inside the nRF24 driver (RF24::write) is standard flush when transmission fails:

//Max retries exceeded
if( status & _BV(MAX_RT)){
  flush_tx(); //Only going to be 1 packet int the FIFO at a time using this method, so just flush
  return 0;
}

[hek]

@Yveaux

Ohh.. nice digging anyway.