[Open-graphics] Multipliers in oga1hq
Farhan Mohamed Ali
farhan at cmu.edu
Sun Sep 2 20:33:31 EDT 2007
On Sat, September 1, 2007 6:59 pm, Petter Urkedal said:
> On 2007-09-01, Farhan Mohamed Ali wrote:
>>> So, let's consider integrating Farhan's version in the
>>> nanocontroller. Given that the VGA code will use 16 bit, would it be
>>> better to reduce the multiplier to 16x16->32? Will this be
>>> insufficient for the DMA code? (Does DMA require multiply at all,
>>> other than powers of 2?) Conversely is 33 cycles multiply to slow for
>>> the VGA code, and would 17 cycles be fast enough?
>> 16x16 will take 9 cycles. Perhaps it could be fast enough to be
>> clocked at 200mhz if it is a dedicated 16x16 part. I'll try this out. I
>> will also try adding a special mode to the current 32x32 version that
>> assumes 16 bit inputs and takes 9 cycles to complete for that mode.
> To complete your corrections, the 32x32 radix-4 multiplier is 17 cycles,
> not 33 as I said. I think a 16x16 mode is more interesting than
> early-termination. Now, we're also getting down to quite manageable
> delays, as seen from the programmer trying to fill in the instruction
> slots. This also means the cycles used on I/O become more important.
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Attached is the new version with a 16 bit mode switch (input 0 detection
removed). Inputs are assumed to be 16bit sign extended to 32bits. Output
is 32bit sign extended to 64bits. This design achieves 128MHz. Also added
in the copyright and license statement.
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