[microblaze-uclinux] MPEG-4 Codec

["Steve Spano" <steve@xxxxxxxxxxxxx>]

Hi Folks,

Thanks John for clearing up the sys-call process.

Does anyone know where I can get a H.264 compression codec for Linux? I
think there are some sources floating round somewhere. 

Thanks

Steve Spano
FLE


-----Original Message-----
From: owner-microblaze-uclinux@xxxxxxxxxxxxxx
[mailto:owner-microblaze-uclinux@xxxxxxxxxxxxxx] On Behalf Of John Williams
Sent: Sunday, November 19, 2006 10:08 PM
To: microblaze-uclinux@xxxxxxxxxxxxxx
Subject: Re: [microblaze-uclinux] ### kernel thread function

Hi Steve,

Steve Spano wrote:

> I have a few questions.
> 
> Mostly,
> 
> 	asm volatile (	"addik	r12, r0, %1	\n\t"
> 			"addk	r5, r0, %2	\n\t"
> 			"brki	r14, 0x8;	\n\t"
> 			"addk	%0, r3, r0	\n\t"
> 		        : "=r" (ret)
> 			: "i" (__NR_clone), "r" (arg0)
> 		        : "r3", "r4", "r5", "r12", "r14", "cc");
> 
> It looks like this routine is saving the current PC into R14 and then
> branching to 0x0000:0008. Isn't this the user interrupt vector? What is
> supposed to be loaded here? Something to support context switching?

This is the mb-uclinux system call interface.  You'll see exactly the 
same construct in e.g. include/asm-microblaze/unistd.h

Loading r12 with the syscall number, r5-r10 with the parameters, then 
issuing brki r14, 0x8 is a system call.

In this case, it's doing a clone() to create a new kernel thread.  The 
only thing microblaze-specific here is the mechanics of issuing the syscall.

Hope this clarifies things for you.

John
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