Hi Jerry,
On Monday 21 April 2008 17:16, Jerry Van Baren wrote:
Matthias Fuchs wrote:
Hi,
after going through the boom code I found out, that setting the 'autostart' variable to 'no' brings me a little closer to what I want. But finally I end up in the enable_interrupts() at the very end of do_bootm(). This freezes my system. The reason for this is the Linux kernel image that is loaded to address 0 and that overwrites the vector table. So reenabling the interrupts in U-Boot with Linux interrupt table is a bad idea.
No, having your (u-boot) interrupt go off while booting linux is a bad idea.
U-Boot calls disable_interrupt() in do_bootm(). That's fact.
Which interrupt is going off? Why is it going off (why isn't the hardware put into a quiescent state)?
So what's the best idea to fix this? I could copy the vector table onto the stack in do_bootm() and copy it back just before reenabling the interrupts.
NO NO NO.
At least this works :-)
Any better idea?
Matthias
That a u-boot initialized interrupt is occurring is wrong and needs to be fixed.
- Traditionally, u-boot does not use interrupts for anything, thus this
isn't a problem.
- Proper hardware and device driver convention is that the hardware must
be quiescent when linux is started and the linux device driver must (re)configure that hardware the way it wants/needs. Obviously, this is probably a 95% rule (console I/O, memory initialization, some others may violate this rule for practical reasons).
- If your u-boot enables interrupt(s), you MUST disable the interrupt
source before starting linux. There is NO graceful way of getting linux to handle an interrupt that was a result of u-boot's running. Starting linux with interrupts disabled is not a good solution - you may get lucky but leaving an active interrupt source is a dangerous game. At best, it is a race condition that you may happen to win today.
So this means that U-Boot calling disable_interrupts before booting Linux (see do_bootm) is correct. Later my the kernel images is loaded at address 0. This overwrites all U-Boot vectors in the first 16k of RAM. So when after the kernel is loaded to address 0 and the ramdisk CRC checking failed to control is to be passed back to U-Boot it sees a mixed up vector table. I think the only ways to fix this is to save the table (as I did for testing) or check the ramdisk images before uncompressing the kernel at address 0.
Except from that I just noticed that 'autostart=no' does not help me, because it completely disables booting the kernel from bootm.
So how can I achive this:
bootm $(kernel_addr_in_flash) $(randisk_addr_in_flash); run load_images_from_usb_to_ram; bootm $(kernel_addr_in_ram) $(ramdisk_addr_in_ram)
So the the initial bootm fails because of invalid images, U-Boot should load images from a USB media and start them.
Matthias