remove useless ce() call

[2bndy5]

resolves #986

[github-actions]

Memory usage change @ e5ed6c0

Board	flash	%	RAM for global variables	%
arduino:avr:nano	💚 -6 - 0	-0.02 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrzero	💚 -8 - 0	-0.0 - 0.0	0 - 0	0.0 - 0.0

Click for full report table

Board	examples/GettingStarted flash	%	examples/GettingStarted RAM for global variables	%	examples/AcknowledgementPayloads flash	%	examples/AcknowledgementPayloads RAM for global variables	%	examples/ManualAcknowledgements flash	%	examples/ManualAcknowledgements RAM for global variables	%	examples/StreamingData flash	%	examples/StreamingData RAM for global variables	%	examples/MulticeiverDemo flash	%	examples/MulticeiverDemo RAM for global variables	%	examples/InterruptConfigure flash	%	examples/InterruptConfigure RAM for global variables	%	examples/scanner flash	%	examples/scanner RAM for global variables	%	examples/encodeRadioDetails flash	%	examples/encodeRadioDetails RAM for global variables	%
arduino:avr:nano	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	-6	-0.02	0	0.0	0	0.0	0	0.0
arduino:samd:mkrzero	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	-8	-0.0	0	0.0	0	0.0	0	0.0

Click for full report CSV

Board,examples/GettingStarted<br>flash,%,examples/GettingStarted<br>RAM for global variables,%,examples/AcknowledgementPayloads<br>flash,%,examples/AcknowledgementPayloads<br>RAM for global variables,%,examples/ManualAcknowledgements<br>flash,%,examples/ManualAcknowledgements<br>RAM for global variables,%,examples/StreamingData<br>flash,%,examples/StreamingData<br>RAM for global variables,%,examples/MulticeiverDemo<br>flash,%,examples/MulticeiverDemo<br>RAM for global variables,%,examples/InterruptConfigure<br>flash,%,examples/InterruptConfigure<br>RAM for global variables,%,examples/scanner<br>flash,%,examples/scanner<br>RAM for global variables,%,examples/encodeRadioDetails<br>flash,%,examples/encodeRadioDetails<br>RAM for global variables,%
arduino:avr:nano,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,-6,-0.02,0,0.0,0,0.0,0,0.0
arduino:samd:mkrzero,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,-8,-0.0,0,0.0,0,0.0,0,0.0

[2bndy5]

Testing this would require running the examples/scanner/scanner.ino in Arduino IDE (using a radio that returns true for isPVariant()) and any code that calls reUseTX() or writeBlocking() with an unreliable connection to the other node. The only example that uses writeBlocking() is

RF24/examples/old_backups/TransferTimeouts/TransferTimeouts.ino

Line 95 in bae5111

if (!radio.writeBlocking(&data, 32, timeoutPeriod)) { // If retries are failing and the user defined timeout is exceeded

However, I haven't focused on maintaining those old examples...

I think its worth noting that the CirPy lib has been using this patch for years, and I haven't had any problems reported there.

[2bndy5]

Oh, the streamingData examples use reUseTX()! I tested the example (on Linux and PicoSDK) but had no failures reported, meaning no call to reUseTX().

The carrier wave is properly transmitting from examples/scanner/scanner.ino with a radio that returns true for isPVariant(). I'll take that as a good sign.

[2bndy5]

I think its worth noting that the CirPy lib has been using this patch for years, and I haven't had any problems reported there.

Actually, the CirPy lib just clears the status flags and relies on the fact that the radio will attempt to transmit anything in the TX FIFO once the CE pin is cycled. The CirPy lib does not actually use the REUSE_TX_PL command.

    if self.fifo(about_tx=True, check_empty=True):
        return False  # return early if nothing in TX FIFO
    self._ce_pin.value = False
    self.clear_status_flags()  # clear all IRQ flags
    # self._reg_write(0xE3)  # skips REUSE_TX_PL command because TX FIFO is occupied
    self._ce_pin.value = True

I think I did this to allow the radio to move onto the next payload when successful. Otherwise, the radio is stuck re-transmitting the same payload in the top level of TX FIFO until any of the following conditions:

• TX failure
• TX FIFO flushed
• write new payload to TX FIFO (excluding ACK payload uploads). This condition does not guarantee that the new payload gets put in top level of TX FIFO. Furthermore, it is unclear if the re-used payload is discarded once a new payload deactivates the REUSE_TX_PL command. This may cause one duplicated transmission when processing the TX FIFO up to the new uploaded payload, especially if the REUSE_TX_PL is issued when TX FIFO has more than 1 payload queued.

According to datasheet (end of section 7.5.2):

As an alternative to Auto Retransmit it is possible to manually set the nRF24L01+ to retransmit a packet a number of times. This is done by the REUSE_TX_PL command. The MCU must initiate each transmission of the packet with a pulse on the CE pin when this command is used.

[2bndy5]

I have confirmed that this still works. I used the python wrapper to manually create a failed transmission (using writeFast() when no other radio was listening), then invoke reUseTX() when there was another radio ready to receive.

I should still point out that reUseTX() basically spams the same payload until

• the transmission fails
• the TX FIFO is flushed
• a new payload is written
• setting the CE pin LOW. This lib does not directly expose controlling the CE pin, so invoking reUseTX() from user-code on Linux seems unproductive (and slightly counter-intuitive).

Any objections to merging this?

[TMRh20]

Nope, I haven't had a chance to test this, but looks like you have! Looks good!