Monday, 9 November 2020

Key Debounce Delay POKEs

Greg Dionne has been working on a TRS-80 BASIC compiler. In the midst of  corresponding with him about the developments we discussed my normal PEEK(2)ANDPEEK(17023) routine for continuous polling of key input. He then mentioned the "debounce" key delay, which could apparently be adjusted by way of a couple of POKEs.  Here are his comments, which might be helpful for MC-10 BASIC programmers:

More notes for you now that I'm looking at the keyboard routines.

1.  If you want the interpreter to go faster when a key is pressed, set the debounce delay to 1.  (POKE 16925,0 : POKE 16926,1).

2.  To examine the state of the BREAK key, (well, for the compiler at least), take a PEEK at 16955.  255=PRESSED  0=NOT PRESSED

3.  The keys for the KEYSCAN are stored in 16945 to 16952.  This gives you access to each individual key.  So you can tell if more than one key is pressed and which keys.  

4.  CONTROL, SHIFT and BREAK do not have dedicated memory allocated for them. You can query the SHIFT key state via doing a PEEK(3).  But the others will be lost since the interpreter will immediately stomp on the keystrobe after catching a key, so only SHIFT can (reliably) be caught this way.  The compiler will have no trouble querying the other states. 

To see all of this in action:

10 POKE 16925,0:POKE 16926,1 : REM MAKE IT SNAPPY

20 MC=16384:KS=16945

30 FOR I = 0 TO 7:POKE MC+I,PEEK(KS+I):NEXT

40 POKE2,254:POKE 16393,PEEK(3):REM CONTROL

50 POKE2,251:POKE 16394,PEEK(3):REM BREAK

60 POKE2,127:POKE 16395,PEEK(3):REM SHIFT

70 KY$=INKEY$:REM NEEDED FOR COMPILER ONLY

80 GOTO 30

I have added his debounce delay POKES (set to 1) to the following programs and updated my compilations:

DMCHASE

ADVENTUR

ALPHAFOR

BERZERK

BIGRED

BOARDER

CAVERAID

DANTE

DIGDUG

ELAVATOR

FROG

HEIANKYO

LODERUN

METEOR

MOUSE

PENGUINO

QBERT

ROVER

SABOT

SCRAMBLE

TOMB

XRALLY

NOSTRO

ABM

BRICKOUT

FARTGOAL

FLYWHEEL

GRIDFACT

LITTLEBR

MEANIES

MILLIPED

RCHASE

RESCUE

SHOPIFT

SPACEWAL

MCJOUST

PONGNEW

GOLDHUNT

GOTCHA

RCHASE

TANK

MILLI

CAR

It seems to make a noticeable difference.  Movement seems much smoother and responsive.  I'll be adding the POKEs to other programs over the next little while.


2 comments:

  1. Very interesting. By making that change, that speeds up the code since it returns the key status quicker?

    ReplyDelete
  2. Yes. The tight main loop I create for my arcade games are delayed just a little less by the internal scanning routines of BASIC itself. Since I peek the keys directly, such scanning (which is just needed for touch typing) are not needed when keys are being held down continuously as in a game controller.

    ReplyDelete