RMT pin state

[poesel]

If I use RMT to generate a pulse on a pin is there a way to know the current state of the pin?
Ideally something like Pin.IRQ_FALLING that triggers a callback.

I tried to use this but it fails. Most llikely because you can't have RMT and Pin on the same pin at the same time.

Code: Select all

from utime import sleep_us, sleep
import esp32
from machine import Pin

counter = 0

def callback(p):
    global counter
    counter += 1

if __name__ == "__main__":
    pulses = (10,)*48
    r = esp32.RMT(0, pin=Pin(15), clock_div=80)
    p = Pin(15, mode=Pin.OUT,)
    p.irq(trigger=Pin.IRQ_FALLING, handler=callback)
    while True:
        if r.wait_done():
            print(counter)
            counter = 0
            r.write_pulses(pulses, start=1)

Thanks

[poesel]

Hmm, so I guess it is not possible?
That is too bad. RMT pulses are quite stable and could be used for creating the clock signal for a HX711 driver. That would be a great improvement over the current bit banging. But without knowing the state you can not synchronize with the data signal.

[Roberthh]

You may have a look at the drivers here: https://github.com/robert-hh/hx711-lopy ... 711_spi.py
There is a bit-bang and a spi version. The SPI version is pretty stable. Even if the title says Lopy, it is not too specific to Pycom devices. Only the SPI constructor may have to be adapted.
Please note that the SCL pin of SPI is not used. The cloeck for the Hx711 is created with the MOSI pin.

[poesel]

Thanks for the hint but we ran some tests with the SPI version and it showed not difference in stability to the normal driver. So there is no gain for the loss of one pin.

But I have to admit that I did read the data sheet of the HX711 wrongly. I thought the clock signal must have a maximum length of 50us. But actually it is only the high signal that must be shorter than 50us. And this works with normal bit banging well enough.
The total signal length is quite unsteady but this doesn't seem to be a problem for the HX711.

WRT to the RMT interface it would sure be nice to get some callback functions like we have for Pins.

[JonRob]

What are you trying to accomplish? you can use a pin as RMT, then call deinit and use the the same pin for other things, then init a RMT again maybe?

[SirN Check]

Correct me if I'm wrong!

With a ESP32-WROVER-B and e.g. esp32spiram-idf3-20200703-unstable-v1.12-614-gc2317a3a8.bin:

The RMT example(s) in the Doc's does not work as the
r.write_pulses((1, 20, 2, 40), start=0)
never terminates. ( r.wait_done() = False )

With esp32-idf3-20191220-v1.12.bin it works.
But then loosing the nice carrier.

[pythoncoder]

RMT is under active development on GitHub at the moment. Aims are to support the carrier and to fix bugs. You may want to follow or contribute.

[SirN Check]

Well, I don't know if I am that qualified.

But I got it going, using the same trick I use to get SPI working after the reset button been pressed:

Code: Select all

import esp32
from machine import Pin


r = esp32.RMT(0, pin=Pin(18), clock_div=8, carrier_freq=38000, carrier_duty_percent=30)
r.deinit()  # Needed, else RMT.write_pulses(...) won't terminate.

# and again
r = esp32.RMT(0, pin=Pin(18), clock_div=8, carrier_freq=38000, carrier_duty_percent=30)


# Testing...
r.write_pulses((3000, 800, 500, 800, 500, 30000), start=0)
#sleep(1)
#r.wait_done()  # should be True
r.write_pulses((3000, 800, 500, 800, 500, 30000), start=0)
print('Success')

Question: Is it interesting or do I just create noise?