[Coco] PIA keyboard input?

[Robert Gault]

James Dessart wrote:
> 
> On 7-Dec-03, at 10:02 PM, Robert Gault wrote:
> 
>> That's easy to do if you use the correct algorithm. What is equivalent 
>> to rolling a bit? A power of 2 change is the same thing. So, if you 
>> want a zero bit, the loop would be (in Basic)
>>  for i =1 to 8
>>   poke pia, 255-2^(i-1)
>>  next i
>> The above is going to give you 255-1=254=%11111110, 
>> 255-2=253=%11111101, 255-4=251=%11111011, 255-8=247=%11110111, etc.
> 
> 
> Which is what I had tried.  However, it seems the store instruction 
> isn't triggering the PIA in MESS.  The ROL does, so I'm guessing it's 
> something related to emulation or timing or something of the like... 
> from what I've heard, it's probably not the emulation... here's the code 
> that reads the row:
> 
>     clra
>     std    -21,u    ;movhi: R:d -> -21,u
>     ldd    #1    ;movhi: #1 -> R:d
>     ldx    -21,u    ;movhi: -21,u -> R:x
>             ;ashlhi: d by x
>     leax    -1,x    ;decr shift count
>     bmi .+6
>     aslb
>     rola
>     bra .-6    ;loop
>     comb        ;comqi: R:b
>     stb    -254    ;movqi: R:b -> -254
>     ldb    -18,u    ;zero_extendqihi: -18,u -> R:d
>     clra
>     leax    d,u    ;addhi: R:x = R:u + R:d
>     ldb    -256    ;movqi: -256 -> R:b
> 
> It's taken directly from gcc's output, but should be pretty much the 
> following in C:
> 
>       *((unsigned char *)0xFF02) = ~(1<<i);
>       columns[i] = *((unsigned char *)0xFF00);
> 
> where i is my loop variable, columns is the array of columns.  However, 
> if I do the following:
> 
>       asm( "rol 0xFF02" );
>       columns[i] = *((unsigned char *)0xFF00);
> 
> and a ROL instruction is generated, it works... kinda stumped.  I 
> haven't had a chance to test it with a real CoCo, though, only MESS.
> 
> I've found gcc does seem to generate a lot of code... my little app to 
> scan the keyboard and print out the matrix of rows and columns takes up 
> about 2-3k.  If I rewrote it in assembly, I could probably halve or even 
> quarter that... but in gcc's defence, it does a lot to make sure it 
> keeps variables in check with registers... if I rewrote the function, 
> I'd probably skip a lot of that.
> 
> James
> 
> 
Your code does not seem right to me. The logic should be similar to
   lda  #%11111110
   ldx  #$FF02
   ldy  #$FF00
A@ sta ,x
   ldb  ,y
   orb  #%10000000
   eorb #%11111111        active bits now are the keys pressed
   bsr  test of regB
   orcc #1                 set carry
   rola                   update mask
   bcs A@                 loop until all columns strobed

I don't see how your C code could generate -21,u  -18,u or  d,u since it 
does not seem possible that any of these would be $FF00 or $FF02.

In any case, you certainly should not try to rotate the registers 
directly as that is meaningless. You have to store and read from the 
registers.