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Re: "sel" field in MTC0 instruction?

To: "Babbellapati Syam Krishna (IFIN DC COM)" <>
Subject: Re: "sel" field in MTC0 instruction?
From: Ralf Baechle <>
Date: Tue, 14 Oct 2003 09:13:23 +0200
Cc: "''" <>
In-reply-to: <>
Original-recipient: rfc822;
References: <>
User-agent: Mutt/1.4.1i
On Tue, Oct 14, 2003 at 11:16:20AM +0530, Babbellapati Syam Krishna (IFIN DC 
COM) wrote:

> #define write_32bit_cp0_performance_register(register,value) \
> __asm__ __volatile__( \
> "mtc0\t%0,"STR(register)",sel\n\t" \
> "nop" \
> : : "r" (value));

Which seems to be dervied from an old function which was eleminated months
ago.  Checkout a current mipsregs.h - which also accesses register with
a non-zero selector value.

> "sel" in the above assembly instruction is a value of either 0, 1, 2 or 3
> based on the register which we would like to write.
> "sel" in the above code is newly introduced by us and if there is no sel
> then the code compiles properly but I guess we would always be accessing one
> register only in that case.
> (A similar routine is written using "mfc0" also for reading the values
> back.)
> But this code results in a compilation error:
> {standard input}: Assembler messages:
> {standard input}:41: Error: illegal operands `mtc0 $3,$25,0'
> {standard input}:45: Error: illegal operands `mfc0 $5,$25,1'
> where $25 is CP0_PERFORMANCE register.
> The command used for compilation is:
> mipsel-linux-gcc -c -I /home/syam/linux-2.4.20with095LTT/include/ -Wall -O2
> -fomit-frame-pointer -fno-common -finline-limit=5000 -G 0 -mno-abicalls
> -fno-pic -mcpu=r4600 -mips2 -pipe -DMODULE -mlong-calls tempCache.c

The mtc/mfc syntax is MIP32, didn't exist in MIPS III.

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