How does assembly version of putc work at boot time at low level?
rfefw at gmail.hu
rfefw at gmail.hu
Wed Aug 30 00:31:47 PDT 2017
Ok, I see it now how. Printing out a character on the touchscreen is
done by this macro:
.macro writeb, ch, rb
mcr p14, 0, \ch, c1, c0, 0
.endm
Could somebody explain what does it do?
On Wed, 30 Aug 2017 01:20:38 +0200, rfefw at gmail.hu wrote:
> Hello there,
>
> I am looking at a file from an android kernel source:
> archarmbootcompressedhead.S
>
> There I see a code which I suppose prints out a message to the
> screen,
> code snippet:
>
> putc:
> mov r2, r0
> mov r0, #0
> loadsp r3, r1
> b 2b
>
> What I do not understand is that what sort of branch instruction "2b"
> suppose to mean? Is it may be a system call-like thing? If so, where
> could I obtain a full list of those available system calls? Thanks in
> advance
>
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