[U-Boot-Users] question about interrupt

[Andreas Schweigstill]

Hello!

loody schrieb:
> As far as I know, the cpu will set the PC to irq/fiq vector when the
> these exceptions are triggered. And these pointers are usually at the
> beginning position of bootloader, if bootloader wants to pass these
> functions to kernel, there may be some instructions like "b xxxxxx'.
> 
> If uboot don't handle these exceptions, how the kernel knows these events?

Probably you are confusing a bootloader with something like a BIOS. When
a Linux kernel starts it just copies some data (like information
contained in ATAGS on ARM processors) and activates the MMU. U-Boot just
works when the MMU is disabled because it uses physical addresses.

Usually the interrupt handler code isn't used by *plain* U-Boot, and
on many platforms it may be totally out-dated. The big advantage of this
concept is that you can implement your own interrupt handler without
fearing conflicts with other interrupt handler stuff, so the runtime
behaviour of such a single interrupt handler can be much more
predictable than in complex environments like Linux.

And the answer to the next question which you probably have in mind is:
No, the U-Boot process scheduler or realtime kernel also doesn't use
interrupts because the is no kernel. Everything is based on a main loop.
Yes, on implication is that U-Boot also won't respond to ARP/ICMP ECHO
or similar network requests when it isn't running a network command like
bootp, dhcp or ftp.

And also timer handling is not interrupt driven but instead performed by
polling some hardware timer registers.

Regards
Andreas Schweigstill


-- 
Dipl.-Phys. Andreas Schweigstill
Schweigstill IT | Embedded Systems
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