analogWrite: set the pin as an output for the 0 and 255 endpoints - #653
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ws-asahi wants to merge 2 commits into
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analogWrite: set the pin as an output for the 0 and 255 endpoints#653ws-asahi wants to merge 2 commits into
ws-asahi wants to merge 2 commits into
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The classic Arduino AVR core calls pinMode(pin, OUTPUT) before its val==0 / val==255 branch, and documents that this is deliberate: the analog output pins are not supposed to need a pinMode() call. This core returned from the endpoint branch without ever touching PORTx.DIR, so on a pin that had not already been made an output: analogWrite(pin, 0) left the pin Hi-Z instead of driving it low analogWrite(pin, 255) enabled the pull-up instead of driving it high The normal PWM path ends in _setOutput(), so only these two values were affected - which is precisely where a sketch is most likely to omit pinMode(): fades that start at 0, and on/off control written as analogWrite(pin, 0) / analogWrite(pin, 255). Found on the Wazamono Tachi (AVR64DU32) while checking Pro Micro compatibility: with the pin left Hi-Z, a jumpered neighbour pin read an arbitrary floating level for analogWrite(pin, 0) and a weak pull-up level for 255. digitalWrite() runs first (it writes OUT and turns off any PWM), then the direction is set, so the pin never briefly drives a stale level. digitalWrite()'s classic-AVR emulation leaves PULLUPEN set in the 255 case; that is harmless and matches classic AVR, where the pull-up is disconnected while the pin is an output (DS40002548B 18.3.2.3 and equivalents). Applies to every part this core supports.
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The val==0 / val==255 branch returned without setting the pin direction.
The classic AVR core calls pinMode(pin, OUTPUT) in analogWrite.
(the API docs promise analog output pins need no pinMode call)
So on a pin not already an output:
Only these two values are affected (the normal PWM path ends in _setOutput()).
Additional Information:
megaTinyCore's analogWrite has the same pattern.