Fix: HardwareSerial interrupt callback code not in IRAM

[mikee47]

Supersedes #1604, fixes #1520 and possibly #1602

Lambda inherits code segment of enclosing statement, i.e. flash. Adding IRAM_ATTR doesn't work, even if it's separated out into a different statement. However, placing the entire updateUartCallback method into IRAM_ATTR does work, but is wasteful of RAM. Therefore reverted to regular static callback handler.

[etmmahi]

Well spotted. I tested this fix and it works flawless on my board.
I will close my pull request with the interrupt fix (#1604)
Pse merge with develop

[mikee47]

I didn't try adding [[section(".iram.text")]] to the lambda, which is apparently the correct syntax. I'll try it and report back - this would be a simpler change if it works.

UPDATE: Tried it, didn't work. Oh well. Using static callback would seem to be the safest option.

SmingCore/HardwareSerial.cpp: In member function 'bool HardwareSerial::updateUartCallback()':
SmingCore/HardwareSerial.cpp:171:62: warning: 'section' attribute directive ignored [-Wattributes]
    [](uart_t* uart, uint32_t status) [[section(".iram.text")]] {                                                              ^

[slaff]

@mikee47 Anything more to be done for this PR or it is tested and complete?

[mikee47]

@slaff All done, tested and complete.

[slaff]

Pse merge with develop

@etmmahi the PR is merged in develop so please update your develop branch and test.