In 2011-2012, when I dealt with the BBX81 project (an unfinished host for BBC Basic 80), I planned to realize a "HDready" (320x200
) displaying too. I got similar results as B0D0 Wenzel: 6 hi-res lines (continuous 240 bytes) were in center of a 256 bytes chunk, and there was a big (200x4 = 800 bytes) hi-res stack. In that 33 (+1) chunks were 528 bytes (33*16) unusable space, what I found too much, and the 800 bytes stack did not fit on code space (the host's maximal size can be about 3K), so the idea was dropped.
- TheOldHRstack.gif (14.78 KiB) Viewed 5561 times
Step1: we have to change the whole hi-res address just once in a 256 bytes chunk. In the next 5 cases it is enough to change the lower byte only.
Code: Select all
NextLine
add a,40 ; the next line in the 256B chunk
jp dfe_cont ; continue d-file execution (delay)
dfe_cont
jp dfe_ldR ; continue d-file execution
;
;
; ======================================================== the dummy D-FILE
;
df_exec .equ $+$8000
pop hl ; get line address
ld a,h ;
ld i,a ; set MSB
ld a,l ;
;
dfe_ldR .equ $+$8000
ld r,a ; set LSB
ddf_data
.ds 40 ; the line buffer
ret nc ;
;
; ========================================================== HI-RES section
;
HR_stack
.dw df_exec,Line001
.dw NextLine,NextLine,NextLine,NextLine, NextLine
.dw df_exec,Line006
.dw NextLine,NextLine,NextLine,NextLine,NextLine
;
;
.dw df_exec,Line235
.dw NextLine,NextLine,NextLine,NextLine,NextLine
.dw dfe_exit ; the last return address in the HR_stack
;
; ====================================================
; 320x240 pixel hires data (40x256 bytes)
; ====================================================
Line001
; etc
Step2: there are 16 bytes between the 240 bytes parts of hi-res data. Is it possible to insert here that 14 bytes parts of the stack
Yes, it is 
- using an other helper routine, which sets the stack pointer to the next location (and of course the lower byte of the address too).Code: Select all
NextLine
add a,40 ; the next line in the 256B chunk
jp dfe_cont ; continue d-file execution (delay)
ChgStack
ld l,c ; set stack pointer to the end of
ld sp,hl ; the 6th hires line in the chunk
ld a,208 ; addr. of the 6th hires line
dfe_cont
jp dfe_ldR ; continue d-file execution
;
; ======================================================== the dummy D-FILE
;
df_exec .equ $+$8000
pop hl ; get line address
ld a,h ;
ld i,a ; set MSB
ld a,l ;
;
dfe_ldR .equ $+$8000
ld r,a ; set LSB
ddf_data
.ds 40 ; the line buffer
ret nc ;
;
; ====================================================== the HI-RES section
;
HR_stack
.dw df_exec,Line001
.dw NextLine,NextLine,NextLine,NextLine
.dw ChgStack
Line001
.ds 240 ; the 6 hi-res lines
.dw df_exec,Line006
.dw NextLine,NextLine,NextLine,NextLine
.dw ChgStack,0
Line006
.ds 240 ; the 6 hi-res lines
;
;
.dw df_exec,Line235
.dw NextLine,NextLine,NextLine,NextLine
.dw ChgStack,0
Line235
.ds 240 ; the 6 hi-res lines
.dw dfe_exit ; the last return address in the HR_stack
The attachment contains a little demo (and a tool to create it), which is optimised for tape loading:
- the code is as small (and smart
) as possible;- it stores the picture (h-file) in unexpanded format (9600 bytes);
- the size of the ".p"-file is less than 10K;
- if the picture contains more black pixels (ones) than whites (zeros), then the ".p"- (and the ".wav")-file will store the inverse of the picture
(this won't affect the tool's other outputs).
- TheTool.gif (21.37 KiB) Viewed 5561 times
.Enjoy,
Zsolt
ps.: my test machine is under construction, so feedbacks are welcome
and there are (remain) 33x10 = 300 unused/unusable bytes...