OPENCORES.ORG

Hi All,

Hi Michael
it could be. I'll have a look. Also please make sure you use the latest
version, and not some old version.

regards,
Damjan

----- Original Message ----- 
From: "michael scott" <mike.scott@j...>
To: <openrisc@o...>
Sent: Wednesday, July 20, 2005 5:41 PM
Subject: [openrisc] openrisc MAC instructions

> Hi All,
>      In the Openrisc architecture manual under the description
> for l.macrc rD it says:
>
> "Once all instructions in MAC pipeline are completed, the contents of MAC
> is placed into general-purpose register rD and MAC accumulator is cleared"
>
> however on running the code below the MAC does't appear to stall/halt and
> the current value in the MAC pipline is used as opposed to the final value
>
> The workaround is (as shown) to stick a couple of l.nops to allow
> time for the pipline to empty. Howver I would expext the hardware to
> automatically wait on reading the spec
>
> #---------------------------------------------------------------------------
> ---
> # Multiply-Accumulate Test
> #---------------------------------------------------------------------------
> ---
>
>    l.movhi  r2,0x0000             # 2 -> r2 (1st multipier)
>    l.ori    r2,r2,0x0002
>    l.movhi  r6,0x0000             # 16 -> r6 (2nd multipier)
>    l.ori    r6,r6,0x0010
>    l.macrc  r4                    # read MACHi;MACHl into r4 & clear the
> MAC accumulator
>
>    l.mac   r2,r6                  # MAC = 0x20
>    l.mac   r2,r6                  # MAC = 0x40
>    l.mac   r2,r6                  # MAC = 0x60
>    l.mac   r2,r6                  # MAC = 0x80
>    l.mac   r2,r6                  # MAC = 0xa0
>
> #   l.macrc r4                     # 0x60 -> r4  FAIL!
>
>    l.nop                          # wait for MAC pipeline to complete
>    l.nop
>    l.macrc r4                     # oxa0 -> r4 OK !
>
>
> _end:
>      l.j _end
>      l.nop
>      l.nop
>      l.nop
>      l.nop
>
> Is this a bug in the openrisc ?
>
> regards,
>
> Mike Scott
>
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