Re: A92: Hi, I have a question too.
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Re: A92: Hi, I have a question too.
Hallo!
I think I know, what caused the problem: When a key is pressed, one of
the Auto-Ints is triggered periodically 300 times per second. This
interrupt is in use by the TIOS and checks all the keyboard matrix for
keypresses (I'm not sure, maybe that auto-interrupt only sets a flag,
and the 300Hz timer interrupt (another Auto-Int) will do the keyboard
read). The problem is just, that this keyboard interrupt changes the
keyboard matrix, which keeps you from reading correctly. So you should
switch off interrupts before reading.
You should also consider to use a little longer delay for reading, since
the required time differs from calculator to calculator and depends
on the battery power etc. (I figured out that 3 times 'move.l (a7),
(a7)'
is sufficient).
Hope this helped.
David Kühling
Kevin Rees schrieb:
>
> I am learning assembly for the 68K. I have been working on writing a
> library for reading keypresses. It is capable of checking a specified key
> to see if it is held down or not. It returns 1 if the key is held down, and
> 0 if not. I am accomplishing this by writing the row mask of the key to be
> checked to [600018].w pausing briefly (using about 6 NOP instructions) and
> then reading [60001B].b and checking the bit coresponding to the column of
> the key being read. (see LowLevel.txt) I used the same format as is used by
> "Fernando3" for reading the keys. My program works fine except for one
> little bug. When any key in the same column is pressed (rows 0-6 only) the
> function thinks that the key specified is also pressed. I have been working
> on this for 3 days now, and have now gathered more info. It seems that once
> out of every 2 times that [600018] is written and then [60001B] is read it
> returns the correct result (a byte containing the state of columns 0-7 in
> the row specified by the mask)
> However every 2nd time the port is written and then read it returns a byte
> coresponding to to a seemingly random row between 0 and 6 (Hence the problem
> mentioned earlier). The program that is calling this function is just an
> infinite loop with the key check inside, and a conditional jump out of the
> loop (when the key specified is pressed). it looks something like this:
>
> main_loop:
>
> move.l <key code>,d0
> jsr check_key
> tst.b d0
> beq exit
> bra main_loop
>
> exit:
> rts
>
> <key code> is a value between 0 and 80 in the format of
> bit 7 6 5 4 3 2 1 0
> X X X X X X X X
> |-----| <- 3 bits (0-7) coresponding to column of key
> |-------| <- 4 bits coresponding to row of key (0-9)
>
> and the check_key function looks something like this
>
> movem.l d1-d3,-(a7) ; save registers
>
> move.l d0,d1
> andi.l #7,d1 ; finds column
>
> move.w #$FFFF,d2 ; used for row mask
> lsr.b #3,d0 ; finds row
> bclr.w d0,d2 ; sets row mask
>
> move.w d2,$600018 ; write row mask to I/O
> nop ; \
> nop ; \
> nop ; \ wait for I/O
> nop ; / to recover
> nop ; /
> nop ; /
> move.b $60001B,d3 ; read I/O
> not.b d3 ; invert d3
>
> btst.b d1,d3 ; test column
> beq key_not_pressed
> movem.l (a7)+,d1-d3 ; restore registers
> move.l #1,d0 ; return 1 if key is pressed
> rts
>
> key_not_pressed:
> movem.l (a7)+,d1-d3 ; restore registers
> move.l #0,d0 ; return 0 if key not pressed
> rts
>
> It is pretty simple code, yet it is giving me a huge headache. I have found
> that by repeating the Write and Read section of the code and then doing a
> logical AND on the 2 results, I can get an accurate read on the key
> specified (hence the conclusion that at least 1 out of 2 reads is accurate)
> but doing so takes extra processor time, and is inconvenient. If any of you
> have any ideas on how I can solve this please let me know.
>
> Thanks
>
> Kebes
>
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