esp8266: put pin interrupt handler in iRAM

[dpgeorge]

Attempt to fix #5714

[dpgeorge]

@peterhinch if you could test this, that would be great.

[peterhinch]

OK, I now have a test running but it needs to run for a while as the fault was infrequent.

You managed to replicate my original report here so maybe that would be worth repeating?

[peterhinch]

This has now run for over two hours - I'm confident this has fixed it. Previously I doubt it ever ran for more than 15 minutes (without pinging).

This also confirms my belief that the I2C issues were a consequence of the ISR not running - this was breaking the protocol causing the Pyboard I2C slave to fail.

[peterhinch]

I have also run your test. I reduced the PWM frequency to 50Hz (10ms interrupt interval) as I thought 1ms rather ambitious for soft IRQ's. This has run for 30 minutes without error.

On occasion it reconnected to the LAN but the code continued to run:

165577
165677
state: 5 -> 2 (6c0)
rm 0
pm close 7
165777
reconnect
state: 2 -> 0 (0)
scandone
state: 0 -> 2 (b0)
state: 2 -> 3 (0)
state: 3 -> 5 (10)
add 0
aid 4
cnt 
165877

connected with misspiggy, channel 3
dhcp client start...
165979
ip:192.168.0.18,mask:255.255.255.0,gw:192.168.0.1
166079
166179

Code:

from machine import Pin, PWM
from time import sleep
import gc

pin = Pin(13, Pin.IN)
count = 0
def cb_pin(_):
    global count
    count += 1

ei = pin.irq(handler = cb_pin, trigger = (Pin.IRQ_FALLING | Pin.IRQ_RISING))
PWM(machine.Pin(2), freq=50, duty=50)
while True:
    sleep(1)
    print(count)
    gc.collect()

[dpgeorge]

You managed to replicate my original report here so maybe that would be worth repeating?

That was actually something subtly different: it didn't lead to a crash, rather it hung the Python code but the "OS" was still running.

This has now run for over two hours - I'm confident this has fixed it.

Ok, that's really great news! But let's wait a bit to merge this in case something else comes up.

[dpgeorge]

I cleaned this up a bit and removed support for hard=True in the Pin.irq() method (because it's no longer possible for this to work). Setting that option will now raise a ValueError.

[dpgeorge]

Added a small note to the docs that the hard argument may not be supported on certain ports.