Answering to myself to try and provide more background info:
As a follow up to my previous messages, I now have a working kernel and a
working bootloader... but not when they are both together.
Case in point:
- load zImage.elf to DRAM 0x400000 with JTAG debugger. Run it. It runs
fine.
- Load Bootloader.elf to BRAM 0xFFFF0000 with JTAG debugger. Run it. It
runs fine (but it doesn't do much yet).
- Now load both of the previous ones, and have the bootloader perform a
jump to kernel:
void main() {
typedef void tFunc(void);
((tFunc *)0x400000)();
}
Now if the bootloader _only_ contains the above code, the kernel runs
perfectly.
Unfortunately I need to do some things in the bootloader: I use 3 GPIOs to
control a frontal set of LEDs, to get a card number and to load/unload a
serial flash memory. Those operations work. But here is the strange thing
that leads me to believe there are interrupt interferences.
If I just read from a GPIO before launching the kernel, it boots fine, with
a few NFS errors when mounting the rootnfs:
[ 4.360060] Freeing unused kernel memory: 76k init
[ 11.432269] nfs: server 192.168.1.185 not responding, still trying
[ 11.441186] nfs: server 192.168.1.185 OK
init started: BusyBox v1.10.1 (2008-04-24 12:26:38 CEST)
genepy login:
Now if I also write to a 2nd GPIO, I get a lot more NFS errors.
And if I also access the flash through the 3rd GPIO, the kernel hangs:
loaded at: 00400000 004EA19C
board data at: 004E8120 004E819C
relocated to: 0040405C 004040D8
zimage at: 00404E48 004E7A7E
avail ram: 004EB000 08000000
Linux/PPC load: console=ttyUL0,115200 rw root=/dev/nfs ip=bootp
Uncompressing Linux...done.
Now booting the kernel
But then it hangs for exactly 3 minutes, nothing on the serial port,
before the bootloader restarts.
Why should the behavior be different whether it's started from the
debugger or from my bootloader ?
Now I've defined my hardware project using interrupts on the GPIOs, which I
don't need and frankly they don't make sense for an output GPIO. I would
like to try to compile a kernel without GPIO interrupts, unfortunately the
compilation fails:
$ make ARCH=ppc CROSS_COMPILE=powerpc-linux-uclibc-
[...]
CC arch/ppc/syslib/virtex_devices.o
arch/ppc/syslib/virtex_devices.c:535: error: 'XPAR_INTC_0_GPIO_0_VEC_ID'
undeclared here (not in a function)
Question breakdown:
- do I need interrupts for GPIOs ?
- how can I compile the ppc 2.6.25 kernel without them ?
- Why do I have problems running the kernel if the bootloader makes use of
the GPIOs ?
- does the bootloader need to perform some kind of special cleanup before
calling the kernel ?
Thanks a lot for shedding a light on those mysteries.
--
Guillaume Dargaud
http://www.gdargaud.net/
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