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s-matyukevich / raspberry-pi-os

Learning operating system development using Linux kernel and Raspberry Pi
MIT License
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Possible missing of GPPUD control signal removal #259

Open foxhoundsk opened 1 year ago

foxhoundsk commented 1 year ago

Per the following procedure, one should write to GPPUD to remove the control signal: https://github.com/s-matyukevich/raspberry-pi-os/blob/31fc1481f529ba1a72a8a6bc62dc488b84fc2cdb/docs/lesson01/rpi-os.md?plain=1#L345

However, there has only the following operation at the epilogue: https://github.com/s-matyukevich/raspberry-pi-os/blob/31fc1481f529ba1a72a8a6bc62dc488b84fc2cdb/docs/lesson01/rpi-os.md?plain=1#L356

Do we need to add put32(GPPUD,0); at the epilogue to remove the control signal?

seusher commented 1 year ago

Technically the docs say that this needs to be done, but because the code doesn't rely on pull-up or pull-down, it already sets GPPUD to 00, which represents Off – disable pull-up/down, so there isn't any need to update the value again.