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Assembly: How to save RAM, and how to print RAM to the screen
Posted: Thu Dec 23, 2021 5:22 pm
by rje
I have a two-parter question.
1. How might I dump a screen of PETSCII to a binary file?
I print splash screens and similar, storing the content char arrays in C, or sometimes programmatically printing it out. I’d like to store that data in a binary. I’m not sure how to do that from the X16.
2. Then of course I want to write a short asm that prints that to the screen. The only way I think of this is by using FFD2, but maybe there are better ways? Also note problems with my code here!
entry:
lda clear-screen-code
jsr $ffd2
ldx #0
printloop:
lda $8000,x
cmp $ff or whatever makes sense here
beq done
jsr $ffd2
inx Uh oh that won’t work because x is only 8 bits.... can I increment A indirectly?
jmp printloop. But I know there’s a better way to do that.
done:
rts
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Thu Dec 23, 2021 6:36 pm
by TomXP411
The general solution is to
1. read up on file I/O using KERNAL calls I’ll dig out my ASM directory program for you. It might also be in the file section here
2. use a 16 bit counter. This involves doing the usual INC and checking the carry flag.
This opens a file for reading. I believe to write to the file, you'd use CHKOUT at the end.
lda #filename_len-filename
ldx #<filename
ldy #>filename
jsr SETNAM
lda #FILE_CHANNEL
ldx #DEVICE_NUMBER
ldy #SECONDARY_ADDRSS_DIR
jsr SETLFS
jsr OPEN
ldx #FILE_CHANNEL
jsr CHKIN
After that, calls to CHRIN or BASIN would read from the disk channel. To change back to the screen
JSR CLRCHN
I've attached my directory reader ASM and my labels for your reference.
labels.asm dir.asm
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Thu Dec 23, 2021 7:09 pm
by Greg King
On 12/23/2021 at 12:22 PM, rje said:
I have a two-parter question.
1. How might I dump a screen of PETSCII to a binary file?
I print splash screens and similar, storing the content char arrays in C, or sometimes programmatically printing them out. I’d like to store that data in a binary. I’m not sure how to do that from the X16.
2. Then of course I want to write a short asm that prints that to the screen. The only way I think of this is by using $FFD2, but maybe there are better ways? Also note problems with my code here!
entry:
lda clear-screen-code
jsr $ffd2
ldx #0
printloop:
lda $8000,x
cmp $ff; or whatever makes sense here
beq done
jsr $ffd2
inx ; Uh oh, that won’t work because x is only 8 bits. Can I increment A indirectly?
jmp printloop. ; But, I know there’s a better way to do that.
done:
rts
Answer #2:
You must read the text through an indirect pointer. Use two nested loops. Increment the index in the inner loop. Increment the high byte of the pointer in the outer loop.
entry:
lda #clear-screen-code
jsr CHROUT
lda #<$8000
ldx #>$8000
sta r0
stx r0+1
ldy #0
loop:
lda (r0),y
beq done
jsr CHROUT
iny
bne loop
inc r0+1
bra loop
done:
rts
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Thu Dec 23, 2021 8:00 pm
by Greg King
What kind of data do you want to put in a file?
Some text before it's printed.
Or, something that you programmatically formatted and printed onto the display screen?
(If it's the second kind, then you will have screen-codes in VRAM, not PetSCII in main RAM.)
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Thu Dec 23, 2021 11:34 pm
by ZeroByte
Does VSAVE exist? If so just do that and do VLOAD to put it on the screen.
In assembly, VLOAD is:
Usual call to SETNAM/ and usual call SETLFS with A=0, X = 8 and Y=0
Then call LOAD with A=2|3 and XY = VRAM address. (A = bank+2)
(edited to fix erroneous info)
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Thu Dec 23, 2021 11:39 pm
by ZeroByte
If no VSAVE then copy the screen tile map data from 00000 to 03FFF into main memory from 5000
Then do a normal call to save giving 5000 to 8FFF as the area to save.
SAVE doesn’t work right for HiRAM yet (at least not in the Kernal) which is why I suggested Main memory.
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Fri Dec 24, 2021 3:53 am
by Greg King
On 12/23/2021 at 6:34 PM, ZeroByte said:
Does VSAVE exist? If so just do that and do VLOAD to put it on the screen.
In assembly, VLOAD is:
Usual call to SETNAM.
Call SETLFS with A=2 or 3 (VRAM bank + 2), X = 8, and Y=0.
Then call LOAD with A=0 and XY = VRAM address.
That's BASIC's way of doing it. In Assembly, SETLFS doesn't take anything in the accumulator for LOAD/SAVE calls. And, the "VRAM bank + 2" is put into the accumulator of the LOAD call (i.e., the 17-bit VRAM address is given directly to the LOAD call).
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Sat Dec 25, 2021 2:28 pm
by rje
THANK YOU! Now some more questions.
lda #<$8000
ldx #>$8000
Are the < and > operators how we split a word into low and high bytes?
Second question. Can I just directly increment a memory location, and use the carry bit to increment the high byte?
That might look messier than nested loops...
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Sat Dec 25, 2021 2:31 pm
by rje
And, merry Christmas!
Assembly: How to save RAM, and how to print RAM to the screen
Posted: Sat Dec 25, 2021 2:59 pm
by Stefan
On 12/25/2021 at 4:28 PM, rje said:
lda #<$8000
ldx #>$8000
Are the < and > operators how we split a word into low and high bytes?
Yes.
On 12/25/2021 at 4:28 PM, rje said:
Can I just directly increment a memory location, and use the carry bit to increment the high byte?
I'm not sure what you exactly mean. However, the INC, INX, INY, and INA opcodes don't affect the carry bit, so I guess the answer is no.
In
@Greg King's post above, there is a complete code sample using the Y register to walk through the low byte of the address. As may be seen in the sample, wrap around of Y is tested by checking for 0, not carry (the row BNE LOOP in Greg's code).