Paolo Mantegazza wrote:
> If you disable the cache then things are more stable but you can be
> catched by the raptus to throw the PC out of the window.
Yes, I agree that a PC just isn't suitable for many jitter-free hard
real time tasks. I wrestled for a while trying to do some (not too
time-critical) PWM, and gave up.
Attached is some DOS code which disables the cache on an Intel processor
supporting these 486 instructions. My AMD586-133 machine ran terribly
slow, unable to keep up with 115200bps serial, after disabling the
cache.
--
Steve Rosenbluth
Jim Henson's Creature Shop
2821 Burton St, Burbank CA
; file: discache.asm
; sets sr0 bit 30 to disablef on-chip cache
; Steve Rosenbluth, JHCS 3-23-1999
.MODEL large
.STACK 100h
.DATA
cache_still_used DB 'Cache could not be disabled.',13,10,'$'
cache_disabled DB 'Cache is DISABLED.',13,10,'$'
.CODE
mov ax,@data
mov ds,ax ; set ds to point at data
P486 ;allow 486 protected mode instuctions
mov edx,cr0 ;get cr0
push edx ;save cr0 on stack so we can see it
or edx,40000000H ;set bit 30 high
push edx ;save cr0 on stack so we can see it
mov cr0,edx ; disable the cache
mov edx,cr0 ;get cr0
push edx ;save cr0 on stack so we can see it
and edx,40000000H ;clear bits other than bit 30
xor edx,40000000H ;see if bit 30 high, zflag gets set if it is
jz success ;go to "yes" if zero flag is set
failed:
mov dx,OFFSET cache_still_used
jmp print_string
success:
mov dx,OFFSET cache_disabled
print_string:
mov ah,9 ;dos print string func val
int 21h ;dos int
mov al,0 ; normal return value
.EXIT
END
discache.exe