Re: 8051 Speed Optimization

alexmchale@xxxxxxxxx wrote:

I'm working on optimizing code for a C8051F120 that needs to run at an
extremely fast clip.  The following few lines are repeated over, as
fast as possible.  The looping is a straightforward djnz.  The bulk of
the cpu time is spent on the following lines.  This is repeated (cut
and paste, but with the binary value changed) 8 times per loop.

; for reference
rLEVEL           equ   R0
mDATAOUT         DATA  64

; the code
            row0:
                movx    A, @DPTR
                inc     DPTR
                subb    A, rLEVEL
                jc      row1
                orl     mDATAOUT, #00000001b
            row1:


how about having mDATAOUT in bit addressable area
and then doing:

	subb A,rLEVEL
	mov  C,mDATAOUT.0
row1:

Note, the subb you are using depends on the state of Carry,
so your present code has some LSB strangeness:^)
(you eventually could use an add instruction and
then complement mDATAOUT after you processed all 8 bits)

Greetings,

Frieder
.