How to recover from config.txt problem?

[bobgardner]

Howdy folks. I have a pi0W with a hdmi to vga adapter for a monitor, and a wifi mouse and keyboard plugged into the usb. My project is to bring up this cute little 2" round 480x480 tft using DPI and 666 mode. This will use all but a couple of the gpios, and it involves editing the config.txt to put it into the mode that uses the parallel interface. Nothing ever works the first time, so my question is, if I turn on force vga mode in the config.txt, will I still have the desktop on the hdmi out, even if I need to edit the config.txt again? In otherwords, how do I recover from boogering the config.txt? Can I stick the sd card into a card reader on a pc and see the file? Maybe not because its ext4? Other ideas? Thanks.

[trejan]

Can I stick the sd card into a card reader on a pc and see the file?

Yes. The /boot partition is FAT32 so basically everything can modify it.

[FTrevorGowen]

Howdy folks. I have a pi0W with a hdmi to vga adapter for a monitor, and a wifi mouse and keyboard plugged into the usb. My project is to bring up this cute little 2" round 480x480 tft using DPI and 666 mode. This will use all but a couple of the gpios, and it involves editing the config.txt to put it into the mode that uses the parallel interface. Nothing ever works the first time, so my question is, if I turn on force vga mode in the config.txt, will I still have the desktop on the hdmi out, even if I need to edit the config.txt again? In otherwords, how do I recover from boogering the config.txt? Can I stick the sd card into a card reader on a pc and see the file? Maybe not because its ext4? Other ideas? Thanks.

1) If you've enabled SSH and can login over the network you can edit config.txt w/o using another m/c.
2) But maybe better to make use of config.txt's conditional filters? https://www.raspberrypi.org/documentati ... itional.md
Trev.

[DougieLawson]

Can I stick the sd card into a card reader on a pc and see the file?

Yes. The /boot partition is FAT32 so basically everything can modify it.

You don't even need to edit it. Just rename the broken file to config.txt~, then create a new empty file. The system will come up with an empty file (it may not work optimally but will get to a point where you can use Raspbian Linux to repair the broken config).

[thagrol]

Backup the unmodified config.txt first (to, for example, config.bak). That way you have a known good version you can restore via ssh or via another machine.

Dougie's suggestion is fine but there have been times when I've needed/wanted to revert to the stock config.txt and it's a pain having to copy that from another Pi or extract it from an image.

editied for tpyos

[6by9]

One trick I use is to add any testing parameters under a [gpio27=1] tag. GPIO27 (40pin header pin 13) is normally low, so add a jumper between it and 3.3V to activate your test parameters. If it doesn't work, remove the jumper and reboot with your known good settings. Fix config.txt, reapply the jumper, and reboot for a second attempt.

[DougieLawson]

One trick I use is to add any testing parameters under a [gpio27=1] tag. GPIO27 (40pin header pin 13) is normally low, so add a jumper between it and 3.3V to activate your test parameters. If it doesn't work, remove the jumper and reboot with your known good settings. Fix config.txt, reapply the jumper, and reboot for a second attempt.

Tricky. Why isn't that stuff documented somewhere?

[6by9]

One trick I use is to add any testing parameters under a [gpio27=1] tag. GPIO27 (40pin header pin 13) is normally low, so add a jumper between it and 3.3V to activate your test parameters. If it doesn't work, remove the jumper and reboot with your known good settings. Fix config.txt, reapply the jumper, and reboot for a second attempt.

Tricky. Why isn't that stuff documented somewhere?

The use of GPIO conditionals is documented - https://www.raspberrypi.org/documentati ... itional.md

The use to switch between alternate configs was one I came up with a month or two back when developing the KMS driver. Getting it wrong generally meant not booting, so having a quick way to get a bootable system back was useful. I could have used an NFS mount for / instead (probably still should to avoid killing the SD card), but having it on an SD card was more covenient.

[DougieLawson]

Ah, you've added new stuff since I last looked.

I've been using the serial number filters for ages, that means every /boot/config.txt is identical and I've got a master copy and a script to keep them that way.

[davidcoton]

... more covenient.

Ouch, is that a virus hiding there (Sorry, couldn't resist)