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
>
> _______________________________________________
> linux-arm mailing list
> linux-arm at lists.infradead.org [1]
> http://lists.infradead.org/mailman/listinfo/linux-arm [2]

 

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