Post by thread:[OT] Small delays

The 16 bit register used for the 18ms DOS/Windows ticks at 0.8xx us You can get small delays pooling this register. Let's say 400us. So, 400/0.8xx ~= 500. Get the reg value + 500 and keep comparing until you have a >=. Watch out this register wrap from 0xFFFF to 0x0000 JSouto PerErik Klarenfjord wrote: {Quote hidden}> > I work on a program that transfer some data via the LPT port. I need to use > very short delays, but can't figure out how to do them less than 1 us. I > will run the program on different machines and the best results should be to > use interrupts. But how ? > I appreciate any help from you. :) > > /Per-Erik > > ____________________________________________ > > Per Erik Klarenfjord > Third Base Electronics > Triogatan 7 > 656 36 KARLSTAD > > Tel: 054-837852 070-3975147 > E-mail: .....pererikKILLspam@spam@3base.net > > http://www.3base.net

Thanks a lot. Do you know the address to that (0.8xxx us) register ? I noticed some very interesting pages in a book i have. The code can be used with 286, 386, 486 and Pentium.... To create a processor independent delay, IBM made PB4 pf port 61h toggle every 15.085 us. That means that by monitoring PB4 of port 61h, a fixed time delay can be obtained, as shown next from IBM PC AT BIOS. Upon entering this subroutine called WAITF, register CX must hold the number of 15.085 us time delays needed. ;CX = Count of 15,085 us WAITF PROC NEAR PUSH AX WAITF1: IN AL,61h AND AL,10h ;Check PB4 CMP AL,AH ;Did it just change ? JE WAITF1 ;Wait for Change MOV AH,AL ;Save the new PB4 Status LOOP WAITF1 ;Continue until CX becomes 0 POP AX RET WAITF ENDP Example, to create a half-second delay, set CX=33144 (33144 * 15,085 us) = 1/2 second, and then call the above routine as done by IBM PC AT BIOS. The 16 bit register used for the 18ms DOS/Windows ticks at 0.8xx us You can get small delays pooling this register. Let's say 400us. So, 400/0.8xx ~= 500. Get the reg value + 500 and keep comparing until you have a >=. Watch out this register wrap from 0xFFFF to 0x0000 JSouto PerErik Klarenfjord wrote: > > I work on a program that transfer some data via the LPT port. I need to use > very short delays, but can't figure out how to do them less than 1 us. I > will run the program on different machines and the best results should be to {Quote hidden}> use interrupts. But how ? > I appreciate any help from you. :) > > /Per-Erik > > ____________________________________________ > > Per Erik Klarenfjord > Third Base Electronics > Triogatan 7 > 656 36 KARLSTAD > > Tel: 054-837852 070-3975147 > E-mail: pererikKILLspam3base.net > > http://www.3base.net

part 0 5100 bytes > Thanks a lot. > Do you know the address to that (0.8xxx us) register ? The system timer is port $43. There are a number of "gotcha"s. * It is an 8-bit device! You have to use a latch command to read it. * Later machines are not "IBM compatible" - when they "virutalised" the timer chip from the earlier machines, they decided to alter it a bit, make it "simpler" etc. There are some tricks about it I haven't full documentation on. * All timing routines will be distorted by interrupts. Only code based on reading the system timer (or keyboard chip as you mention) will be less severely affected. The system timer is used by Windoze to task switch. If you let it roll over, not only do you have to adjust the count, but you likely lose control for 1/18 of a second at least. * The timer counts *down*. Possible approach, as per attached test code: Wait until the timer has recently rolled over (value about 65000 or so), then initiate the action to be timed, wait for a correspondingly lesser timer count, and finish the timed action. The test code (which does not print out the result until after the time delay finishes) suggests this will be about 99% reliable. If gross overrun 1% of the time doesn't matter, this will work. If you can't accept the overrun, use external hardware. > To create a processor independent delay, IBM made PB4 pf port 61h > toggle every 15.085 us. That means that by monitoring PB4 of port 61h, > a fixed time delay can be obtained, as shown next from IBM PC AT BIOS. That'll be the keyboard controller. Presumably works still in current machines, but same problems as system timer. > The 16 bit register used for the 18ms DOS/Windows ticks at 0.8xx us > You can get small delays pooling this register. Let's say 400us. > So, 400/0.8xx ~= 500. Get the reg value + 500 and keep comparing > until you have a >=. Wrong way. It counts DOWN. > Watch out this register wrap from 0xFFFF to 0x0000 Yes - as above! -- Cheers, Paul B. \\ INTTEST1.SEQ Light Chaser Test ver:1.00 14/10/98 P.B. Webster { ' noop alias immediate DEFINED TARGET-INIT NIP \ Are we target compiling? 0<> #IF ' \ alias \F immediate ' noop alias \T immediate #ELSE ' noop alias \F immediate ' \ alias \T immediate #ENDIF \ *************************************************************************** decimal $278 VALUE PORT VARIABLE TIMER $40 TIMER ! $6C.0040 2CONSTANT times VARIABLE PRVTIME VARIABLE TTIME code RTIME ( -- time ) \ read system timer \T CLEAR_LABELS \T SAVE_BX mov dx, timer \ point to timer add dx, # 3 \ control register sub al, al \ timer zero out dx, al \ latched sub dx, # 3 \ timer zero in al, dx \ get the byte mov ah, al \ hide it in al, dx \ get secnd byte xchg al, ah \ swap them \F 1push \T MOV BX, AX \T RET end-code : TICK? ( --- f ) \ has a tick passed? times @L dup prvtime @ - if dup prvtime ! $FF00 or else drop false then ; : PARTICK? ( delay --- f ) \ has a partial tick passed? rtime ttime @ over - rot > if dup ttime ! else drop false then ; : WAITICK BEGIN TICK? UNTIL ; : WAITQTC BEGIN $4000 PARTICK? UNTIL ; : PPUT ( c --- ) \ write to parallel port port pc! ; : PGET ( --- c ) \ read parallel port port pc@ ; : CPUT ( c --- ) \ write to control register $0B xor port 2+ pc! ; : CGET ( --- c ) \ read control register port 2+ pc@ $0B xor ; \ Control register bit: 0: Pin 1 \ 1: Pin 14 \ 2: Pin 16 \ 3: Pin 17 400 value tard : dally tard 0 do loop ; : poff ( shut off drivers ) 0 pput 0 cput ; poff variable tmax variable tmin variable tstart 1000 tstart ! \ tstart is test delay time : 1stime ( -- time ) \ Waits for 500 < ticks < 1000 and reports begin rtime dup -1000 u< over -500 u> or while drop repeat ; : loint ( -- delay ) \ Waits prescribed delay, reports actual delay 1stime dup tstart @ - begin rtime 2dup u< while drop repeat nip dup u. - dup u. cr ; : int1000 \ Do this a thousand times! cr 0 tmax ! 32000 tmin ! 1000 0 do loint dup tmax @ max tmax ! tmin @ min tmin ! loop tmin @ ." Minimum of" tstart @ . ." = " . cr tmax @ ." Maximum of" tstart @ . ." = " . cr ;