What happens when PORT has more than one state change within your polling interval?
I think that violates Ed's revised spec, Marcel. My interpretation is that transitions occur asynchronously, but don't bunch up too tightly for a reasonable 65xx loop to process.

Ok fair, I missed that.

But then ...

What happens when PORT has more than one state change within your polling interval?

I added a usage text when starting the mini-assembler with EEER. This makes the program a tiny bit larger than 1K, stretching from $BE5 to $FFF now.

But the good thing is that now there's a second entry point that skips the usage text. This extra help code and text runs from $BE5 to $CA7. The mini ...

I replaced my solution with yours. By keeping it inline, the original program grows with just 2 bytes to a grand total of 172. Bravo!

https://github.com/kervinck/gigatron-ro ... ae0d1307f6

Ah, we're looking at different programs. The one I was talking about, and the one that is used in both videos linked above, is two pages earlier in the section titled "TEST PROGRAM."

Ah, I'm learning something new every day. I agree that the 2012 video must be an anomaly. Anyway, the lower case ...

I don't spot any improvement from what I posted.

In the Apple-1 User Manual it jumps back to the clearing of A:

As documented there, the character output translation is:
$00-$1F Print nothing (excepting $0D)
$0D (CR) Moves to the beginning of the next line.
$20-$5F (space through underbar) prints given char
$60-$7F (lower-case etc.) prints same as $40-$5F
($7F is not treated as a control character)
I ...

Certainly past 19. A bad guesser needs many tries. But it doesn't really matter what happens after 99...

That is 10 bytes. The original has 7, so you need 3 bytes to avoid SED. That passes as amazingly clever with me.

[Edited out some of my earlier confusion]

This is my best shot. First put an escape in place with this JSR:


JSR NXTBCD
ADC TRIES ; ADD 1 TO TRIES IN DECIMAL MODE
STA TRIES

Then do the work in these 13 extra bytes:

NXTBCD: LDA TRIES
AND #$F ; Low nibble
CMP #9 ; Is it 9?
BEQ LOW9 ; If yes, add 7
LDA #4 ; Otherwise add 1
LOW9 ...

I'm looking to replace the following snippet with something that doesn't use decimal mode. It should increment TRIES if its lower nibble is under 9, or add 7 if that nibble equals 9. All other cases are "don't care".


; Precondition: A = 0
SEC
SED
ADC TRIES ; ADD 1 TO TRIES IN DECIMAL MODE
STA ...

Ah, that makes sense! I was thinking of racing the beam on an Apple 1 but that didn't mesh with the idea of existing software...
[offtopic] Atari 2600 programmers had it easy with their TIA chip. It took care of an entire scan line while their software could do something else. They even didn't ...

(Hmm, TIA is from the world of Atari - what's the glue which connects the Apple-I application with the TIA output?)
That was a typo, already fixed it.

This effectively reduces the display throughput to about 600 baud (one character per refresh).
Indeed, by emulating the PIA our terminal output ...

I now settled on $EEE as the mini-assembler's entry address. I mapped the code from $C8A..$FDD to do this, and moved the PCADJ routine to free up this nice address without creating a gap.

So the whole package is just 852 bytes, fantastic!

I also added software-based PIA chip emulation. The ...