Re: [Qemu-trivial] [PATCH] Possible wrong microMIPS opcode encoding

[Aurelien Jarno <aurelien@aurel32.net>]

On Wed, Nov 14, 2012 at 10:49:55AM +0800, 陳韋任 (Wei-Ren Chen) wrote:
> Hi all,
> 
>   While reading microMIPS decoding, I found a possible wrong opcode
> encoding. According to [1] page 337, the bits 13..12 for MULTU is
> 0x01 rather than 0x00. Please review, thanks.
> 
> [1] MIPS Architecture for Programmers VolumeIV-e: The MIPS DSP
>     Application-Specific Extension to the microMIPS32 Architecture

This is indeed correct, but I guess the page you meant is 166. Page 337
refers to the original MULTU instruction from the MIPS Architecture for
Programmers Volume II-B: The microMIPS32 Instruction Set.

On the other the microMIPS32 encoding for DSP instruction is not yet
supported.


> Signed-off-by: Chen Wei-Ren <chenwj@iis.sinica.edu.tw>
> ---
>  target-mips/translate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target-mips/translate.c b/target-mips/translate.c
> index f6fc0c2..01b48fa 100644
> --- a/target-mips/translate.c
> +++ b/target-mips/translate.c
> @@ -10385,7 +10385,7 @@ enum {
>  
>      /* bits 13..12 for 0x32 */
>      MULT_ACC = 0x0,
> -    MULTU_ACC = 0x0,
> +    MULTU_ACC = 0x1,
>  
>      /* bits 15..12 for 0x2c */
>      SEB = 0x2,
> -- 
> 1.7.12.3
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net