dat33228@uxa.cso.uiuc.edu (07/25/90)
What's the best way to execute a 2 microsecond delay from 16 bit native mode
(65816) when you don't know what your processor speed is? I want to place
a delay between two toggles of an annunciator (game connector) on the IIgs,
and I want a steady pulse time regardless of whether I'm in normal, fast, or
transwarp mode. Should I opt for an external hardware device or can I check
one of the internal clocks? This program will ultimately end up in the
heartbeat manager, interrupts by VBL every 16.6667 milliseconds.
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Derek Taubert --> derek@mrcnext.cso.uiuc.edu || dat33228@uxa.cso.uiuc.edu .
Anyone who programs or has an idea for a program for the IIgs, PLEASE send .
me mail! .
..............................................................................dlyons@Apple.COM (David A. Lyons) (07/25/90)
In article <1990Jul24.170152.13125@ux1.cso.uiuc.edu> dat33228@uxa.cso.uiuc.edu writes: > What's the best way to execute a 2 microsecond delay from 16 bit native mode >(65816) when you don't know what your processor speed is? I want to place >a delay between two toggles of an annunciator (game connector) on the IIgs, >and I want a steady pulse time regardless of whether I'm in normal, fast, or >transwarp mode. [...] How 'bout forcing 1 MHz mode temporarily, around the code that turns the annunciator on and off? phb pea $e0e0 plb plb ;saved old B and set B = $E0 sep #$20 ;8-bit A register lda $C036 pha and #$7f sta $C036 ;force 1MHz and keep old speed on stack sta $C059 ;turn on the pulse(?) sta $C058 ;turn off the pulse(?) pla sta $C036 ;restore old speed rep #$20 ;back to 16-bit A register plb ;restore old B register I'm not staring at a timing chart at the moment, but the accesses to $C059 and $C058 should give you about a *four* microsecond delay at 1 MHz. If you really want closer to 2uS, you can use this technique instead (direct-page addressing to access the softswitches): phd ;save old D lda #$C000 tcd ;direct page is $C000..C0FF sta <$59 sta <$58 pld ;restore old D This is still 3 cycles per byte. If you *really* want a shorter pulse than that, in 1 MHz mode (which is the only mode you can force easily), you could try this. Summary: Make the processor access $C059 and $C058 consecutively by doing a stack operation. These softswitch accesses are in bank $00 this time, which is fine as long as I/O shadowing is turned on (and it *has* to be for interrupts to work!). php ;save old interrupt state sei ;make DAMN sure no interrupts come through now! tsx ;save old stack pointer lda #$C05A ;one byte past where we want to write tcs ;put the stack pointer there pha ;pushes 2 bytes on the "stack" at $C059 and $C058 txs ;put the old stack pointer back plp ;restore old interrupt state (and other flags) This ought to get you a ONE microsecond pulse. If that's *too* short, try this for 2: replace PHA with SEP #$20, PHA, PHA, REP #$20 or, better yet, replace PHA with PHB PHB. -- David A. Lyons, Apple Computer, Inc. | DAL Systems Apple II Developer Technical Support | P.O. Box 875 America Online: Dave Lyons | Cupertino, CA 95015-0875 GEnie: D.LYONS2 or DAVE.LYONS CompuServe: 72177,3233 Internet/BITNET: dlyons@apple.com UUCP: ...!ames!apple!dlyons My opinions are my own, not Apple's.
rond@pro-grouch.cts.com (Ron Dippold) (07/26/90)
In-Reply-To: message from dat33228@uxa.cso.uiuc.edu Got to thinking about my comment re: your timing problem again... I had thought you wanted a continuous pulse, but then I reread it and realized you only want a one-shot... My suggestion would be to go to normal mode, do your thing, then return to whatever mode you were in. That way you can get an exactly 2 microsecond (well, 2.046 microsecond) timer. All you need is: lda ($e0),y ; y has zero, $e0 has $5r, $e1 has $c0 (annunciator 3) lda ($e2),y ; $e2 has $5e $5F^^^ , $e3 has $c0 if you don't want to get into any IIgs stuff. If you do, then phd ; save direct page pea $c000 ; make $c000 direct page pld lda $5F ; turn it on lda $5E ; turn it off pld ; restore old direct page I still think the best way to do it would be a one-shot timer, where you could turn off the annunciator to prime it, then turn it on for a 2 msec pulse. You wouldn't need to worry about what speed you were running at. UUCP: crash!pro-grouch!rond ARPA: crash!pro-grouch!rond@nosc.mil INET: rond@pro-grouch.cts.com