"Simon Talbot" <simont@nse.co.uk> writes: > Hi All, > > I am trying to modify the kernel in such a way as to be able to write to > a serial port at a very early stage of kernel start-up (as early in > main.c kernel_startup as possible). This is obviously well before > /dev/ttyS0 etc are available. > > The reason for wanting to do this is to talk to a Serially addressed LCD > display on a headless embedded Linux machine I am experimenting with. > > I still want to maintain full serial console on Serial port 1 but would > like to be able to write small amounts of arbitrary character data to > Serial Port 2 (Such as 'Kernel Booting', 'Starting devices' etc. so that > the boot status can be observed on the LCD which is attached to Serial > Port 2. > > The display is only 2 x 16 Characters so obviously a full printk is not > appropriate. > > Can anyone please point me in the direction of some relevant information > or sample code as I am not getting very far and having spent a few days > on this am starting to pull my hair out. I don't find the kgdb patch to be easy reading, but it does what you want to do, namely writing (also reading) a serial port very early in the boot process. There are several kgdb patches, but I'm thinking of the George Anzinger patch that's in Andrew Morton's mm patchset. http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.0-test9/2.6.0-test9-mm1/broken-out/kgdb-ga.patch -- --Ed L Cashin | PGP public key: ecashin@uga.edu | http://noserose.net/e/pgp/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
