Re: ISA bus and SLOW_DOWN_IO
Victor Yodaiken (yodaiken@chelm.cs.nmt.edu)
Tue, 27 May 1997 08:20:12 -0600
On May 26, 11:20am, "Richard B. Johnson" wrote:
Subject: Re: ISA bus and SLOW_DOWN_IO
>> > pusha
>> > popa
>> >
>> >This will access the stack with a known number of processor clocks plus
>> >read/write access time. These accesses are not on the ISA bus.
>>
>The problem is that we need 300 to 600 ns! BogoMips isn't going to do it.
>It is true that we are back to the clock-speeds of the uP, but the RAM
>stack access times dominate. Anything greater than 600 nanoseconds wastes
>time. Anything less than 300 may result in the glitches. This does not
>have to be very accurate.
200Mhz -> 5ns cycle. Elementary forwarding will eliminate even
cache accesses for push pop. Don't see how you get 300 ns out of it.