Re: 66MIPS 8bit microcontroller


"Everett M. Greene" <mojaveg@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:20070727.79EEEE8.7C0E@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
"Wilco Dijkstra" <Wilco_dot_Dijkstra@xxxxxxxxxxxx> writes:

http://www.tezzaron.com/OtherICs/Super_8051.htm

A software floating point implementation on this 8-bit core might take around
200 cycles on average for addition/multiply, so getting a factor 3 speedup
from the floating point hardware sounds feasible. Not very impressive indeed.

I think you'll find that float operations on an 8-bit micro are
going to require much more than 200 cycles. Addition will be of
the order of 1000 cycles and multiply/divide/sqrt nearer 3000.

The FP libraries I wrote for ARM take less than 30 cycles for float add/mul,
and divide takes 60. Yes 8-bitters are slow, but few are 50 times slower!

An 8-bit core will need about 4-5 times as many instructions, so as long as you
can use mostly 1 or 2 cycle instructions you can stay below 200 cycles. Without
a multiply instruction float mul will need up to 400 cycles. Float division can easily
be done within 500 cycles as it is as complex as multiply (Jonathan Kirwan wrote
a float divide for MSP taking 255 cycles).

Wilco


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  • Re: 66MIPS 8bit microcontroller
    ... going to require much more than 200 cycles. ... The FP libraries I wrote for ARM take less than 30 cycles for float add/mul, ... An 8-bit core will need about 4-5 times as many instructions, ... Remember that the MSP430 series have 16-bit data registers. ...
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