Re: Debugger / Emulator / Logic Analyzer for EBSA285 clone board

[Russell King - ARM Linux Admin]

George France writes:
> I will agree that printk's work great when you are into the 'c' code. I find
> the logic analyzer is most useful when I am in the 'S' code of the boot
> loader or the initialization files of the kernel.

A logic analyser is only useful if you have the caches turned off.  If they
are turned on, then you can't really tell what's going on.

However, the same technique I described can be used from the head*.S files
as well, so long as you keep your wits about you (ie, track what registers
are in use at what time).  I have on many occasion done stuff like:

        mov rx, #0x03000000
        add rx, rx, #0x00010000
        mov rn, #'A'
        strb rn, [rx, #0x3f8 << 2]

on the RiscPC to print out characters via the serial port.  If you're careful
with your choice of "rx", you can just repeat the last two instructions at
strategic points throughout the code (don't forget the memory map switch
tho).  It works just as well.  Normally, you can track a non-boot problem down
to about 10 lines of code pretty quickly, and 10 lines isn't too bad to
realise what the problem is.
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