pfeuh Posted February 16, 2014 Share Posted February 16, 2014 (edited) Hello, I use 2 real Atari with PAL video system. As I use sometimes Altirra to test my code, I have noticed the big difference with NTSC vidéo system. For the action, I can't do anything, european players will play not so fast , but for the music, in NTSC, it remind me some Benny Hill music... Is there a software way to know if there is a PAL or NTSC video embedded? Regards, Pfeuh Edited February 16, 2014 by pfeuh Quote Link to comment Share on other sites More sharing options...
Rybags Posted February 16, 2014 Share Posted February 16, 2014 The PAL register on GTIA, location $D014. Value reads 1 for PAL, $F for NTSC. Not 100% surefire since some people run Antic from the other system and Antic decides the framerate. To cover that minute percentage of exceptions as well, the method of detection in assembler is to check the VCOUNT register in Antic, for NTSC it should never exceed value 131 decimal. To have constant music speed, I just maintain a countdown that starts/resets at 5. When it hits 0, skip playback for that frame in NTSC. 2 Quote Link to comment Share on other sites More sharing options...
pfeuh Posted February 16, 2014 Author Share Posted February 16, 2014 To have constant music speed, I just maintain a countdown that starts/resets at 5. When it hits 0, skip playback for that frame in NTSC. Sorry, I did not understand this part (as a non native speaker). I manage the tempo with the number of ticks for each semiquaver, it is in the range 5 - 15. It is this number of ticks that i would like to decrease in case of a NTSC system. Quote Link to comment Share on other sites More sharing options...
Rybags Posted February 16, 2014 Share Posted February 16, 2014 When composing the music, do so assuming PAL system. Then playback in NTSC, typically it's called once per frame. To keep to PAL speed you just skip the playback call every 6th frame. It should be practically undetectable that you're doing this, I've done it with plenty of game/demo situations. 1 Quote Link to comment Share on other sites More sharing options...
pfeuh Posted February 16, 2014 Author Share Posted February 16, 2014 Thanks Rybags, Now I understand. Quote Link to comment Share on other sites More sharing options...
adam242 Posted February 16, 2014 Share Posted February 16, 2014 Not 100% surefire since some people run Antic from the other system and Antic decides the framerate. To cover that minute percentage of exceptions as well, the method of detection in assembler is to check the VCOUNT register in Antic, for NTSC it should never exceed value 131 decimal. As a member of "that minute percentage of exceptions", I wish more programmers would take that route. My machine detects as an NTSC, but plays as a PAL. When certain games (Pac-Man Arcade and Yoomp!, for two examples) adjust for they think is the correct speed, the results are off and way too slow. Nothing against either game (or their programmers), I enjoy them both immensely on my unmolested machines. I just would like it if they ran properly on my 800, as this is my main system. Quote Link to comment Share on other sites More sharing options...
pfeuh Posted February 16, 2014 Author Share Posted February 16, 2014 (edited) >the method of detection in assembler is to check the VCOUNT register in Antic, for NTSC it should never exceed value 131 decimal. I would try to implement this way, but I don't understand. Whatever the video system, graphic 0 for instance has 3 * 8 blank lines + 24 * 8 lines = 216 lines. How can NTSC have less than 216 lines? Edited February 16, 2014 by pfeuh Quote Link to comment Share on other sites More sharing options...
kenjennings Posted February 16, 2014 Share Posted February 16, 2014 http://www.virtualdub.org/downloads/Altirra%20Hardware%20Reference%20Manual.pdf VCOUNT allows the vertical position counter to be read to two-line resolution (that means, the value is incremented every other scan line) . For NTSC, VCOUNT runs from 0 to 131; for PAL, it runs from 0 to 156. 1 Quote Link to comment Share on other sites More sharing options...
pfeuh Posted February 16, 2014 Author Share Posted February 16, 2014 Thanks, it helps. Quote Link to comment Share on other sites More sharing options...
pfeuh Posted February 16, 2014 Author Share Posted February 16, 2014 I get the same value for PAL or NTSC... $7B. For sure VCOUNT grows during the VBI too, I smell something like that. When I uncomment the line which disables the VBI, the program crashes. PALREG = $D014 ; a PAL video should give a 1 RTCLOK_LOW = $14 VCOUNT = $D40B WSYNC = $D40A NMIEN = $D40E NMIEN_DLI_BIT_VALUE = $80 NMIEN_VBI_BIT_VALUE = $40 * = $2000 JMP START VCOUNT_MAX .BYTE 0 HEXTAB .BYTE $10, $11, $12, $13, $14, $15, $16, $17, $18, $19, $21, $22, $23, $24, $25, $26 .MACRO SHOW_ACC PHA AND #$f0 LSR A LSR A LSR A LSR A TAY LDA HEXTAB,Y STA %1 PLA AND #$0f TAY LDA HEXTAB,Y STA %1+1 .ENDM START ;display GTIA PAL register LDA PALREG SHOW_ACC 40040 ; VBI disabled ; LDA #0 ; STA NMIEN LDY RTCLOK_LOW LOOP CPY RTCLOK_LOW BEQ LOOP ;memorize higher VCOUNT during 4-5 seconds LOOP_2 INC 40003 ;wait until next line STA WSYNC ;compare line number to the biggest memorized one LDA VCOUNT CMP VCOUNT_MAX BMI NEXT_LINE ;it's bigger, let's memorize STA VCOUNT_MAX NEXT_LINE CPY RTCLOK_LOW BNE LOOP_2 ;restore VBI ; LDA #NMIEN_VBI_BIT_VALUE ; STA NMIEN ;display biggest line number LDA VCOUNT_MAX SHOW_ACC 40080 LOOP_3 INC 40004 JMP LOOP_3 Quote Link to comment Share on other sites More sharing options...
flashjazzcat Posted February 17, 2014 Share Posted February 17, 2014 This won't work: LDA VCOUNT CMP VCOUNT_MAX BMI NEXT_LINE Try: LDA VCOUNT CMP VCOUNT_MAX BCC NEXT_LINE 1 Quote Link to comment Share on other sites More sharing options...
pfeuh Posted February 17, 2014 Author Share Posted February 17, 2014 Thanks! Now I get $82 for NTSC and $9b for PAL Assuming that I haven't stop the VBI. Reading http://www.6502.org/tutorials/6502opcodes.html#BPL I suppose that BPL and BMI work with the 8th bit of ACC. That is what is marvellous in live: Every days, I learn! This won't work: LDA VCOUNT CMP VCOUNT_MAX BMI NEXT_LINE Try: LDA VCOUNT CMP VCOUNT_MAX BCC NEXT_LINE Quote Link to comment Share on other sites More sharing options...
pfeuh Posted February 17, 2014 Author Share Posted February 17, 2014 (edited) Thank you everybody, It's fixed now. I use this code: RTCLOK_LOW = $14 WSYNC = $D40A VCOUNT = $D40B NTSC_MAX_LINES = $83 SET_NTSC_FLAG LDA #0 STA NTSC_FLAG STA VCOUNT_MAX LDA RTCLOK_LOW ADC #5 ; add 5 or 6 TAY ;let's loop... SET_NTSC_FLAG_LOOP STA WSYNC ;compare line number to the biggest memorized one LDA VCOUNT CMP VCOUNT_MAX BCC SET_NTSC_FLAG_TEST ;it's bigger, let's memorize STA VCOUNT_MAX SET_NTSC_FLAG_TEST CPY RTCLOK_LOW BNE SET_NTSC_FLAG_LOOP ;let's examine result LDA VCOUNT_MAX CMP #NTSC_MAX_LINES BCS SET_NTSC_FLAG_END LDA #1 STA NTSC_FLAG SET_NTSC_FLAG_END RTS VCOUNT_MAX * = * +1 NTSC_FLAG * = * +1 About tempi, I used a pair of tables. Sorry Rybags, I hear the "glitch", that's why I've choosed this way. Tempi are not exactly the sames for NTSC and PAL, But the flow is regular. PAL_VBI_PER_NOTE_TAB .BYTE $09, $07, $06 NTSC_VBI_PER_NOTE_TAB .BYTE $0b, $09, $07 INIT_TUNE ;ACC contains the tune number TAY CPY CURRENT_TUNE BEQ INIT_TUNE_END ;the tune is not the running one, let's continue to initialize STY CURRENT_TUNE ... / ... LDA NTSC_FLAG BNE INIT_TUNE_NTSC LDA PAL_VBI_PER_NOTE_TAB,Y BNE INIT_TUNE_TEMPO INIT_TUNE_NTSC LDA NTSC_VBI_PER_NOTE_TAB,Y INIT_TUNE_TEMPO STA VBI_PER_NOTE ... / ... Feel free to check it, in PAL or NTSC Regards, Pfeuh CHOPPE_IMAGE.zip Edited February 17, 2014 by pfeuh 2 Quote Link to comment Share on other sites More sharing options...
Rybags Posted February 18, 2014 Share Posted February 18, 2014 Be careful with comparing to determine the system. The actual VCOUNT value can be higher than listed for 1 machine cycle until Antic resets it back to zero. What I'd suggest - use SEI at the start, to disable Stage 2 VBlank. That leaves RTCLOCK still updating but ensures the VBlank should be short enough that your code can still see when VCOUNT crosses over from maximum to 0. Find the max value - then just compare with #135 (dec) - Carry Set = PAL, clear = NTSC. 3 Quote Link to comment Share on other sites More sharing options...
Xuel Posted February 18, 2014 Share Posted February 18, 2014 What I'd suggest - use SEI at the start, to disable Stage 2 VBlank. That leaves RTCLOCK still updating but ensures the VBlank should be short enough that your code can still see when VCOUNT crosses over from maximum to 0. Nice. How about the following implementation: wait for VCOUNT=130, then continuously poll VCOUNT and report PAL if VCOUNT reaches 132 or NTSC if VCOUNT goes back to 0. This seems to work in my tests: ; Carry set = PAL ; Carry clear = NTSC detect_pal_or_ntsc sei lda #130 detect_wait_130 cmp VCOUNT bne detect_wait_130 clc detect_loop lda VCOUNT beq detect_done cmp #132 bcc detect_loop detect_done rts Can it be reduced any further? 2 Quote Link to comment Share on other sites More sharing options...
Rybags Posted February 18, 2014 Share Posted February 18, 2014 That's probably close to the simplest way of doing it.Further reduction might be had using extra registers - but the beauty is that the C bit has the result so the caller can do whatever needed from there, like: bcc NTSC or LDA #0 ADC #0 TAY gives a flag/index with NTSC=0 PAL=1 in Y. 3 Quote Link to comment Share on other sites More sharing options...
pfeuh Posted February 18, 2014 Author Share Posted February 18, 2014 (edited) Thanks guys, nice codes. As I'm not so aware about 6502 assembler, it's a pleasure to read such tips. That's probably close to the simplest way of doing it.Further reduction might be had using extra registers - but the beauty is that the C bit has the result so the caller can do whatever needed from there, like: a flag/index with NTSC=0 PAL=1 in Y. OK... but my function has to be renamed in SET_PAL_FLAG I've just implemented color sets for the different levels. As there is a visible difference between PAL and NTSC colors, I ask myself if I have to use this PAL flag to select a color set... But it is probably too much for just a homebrew game, and I am absolutely not an infographist. Edited February 18, 2014 by pfeuh Quote Link to comment Share on other sites More sharing options...
MaPa Posted February 18, 2014 Share Posted February 18, 2014 Something like this could work too... sei loop lda vcount sta wsync beq loop bit vcount bne loop cmp #132 rts 1 Quote Link to comment Share on other sites More sharing options...
Rybags Posted February 18, 2014 Share Posted February 18, 2014 The difference between Pal/NTSC colours isn't near as bad as the 2600 but there are 2 important things to note. Colour 4 on PAL is not red, it's more towards violet/purple. Star Raiders is a classic example of wrong colour selection. Colour 10 on PAL is definately green, maybe with a hint of blue. Colours 1 and 15 are very similar on PAL, on NTSC there's more of a difference. 1 Quote Link to comment Share on other sites More sharing options...
Xuel Posted February 18, 2014 Share Posted February 18, 2014 Something like this could work too... MaPa, I tried yours but it seems to get into an infinite loop for both PAL and NTSC. Does it work for you? Quote Link to comment Share on other sites More sharing options...
Xuel Posted February 18, 2014 Share Posted February 18, 2014 Ah, it was just missing a label: sei loop lda vcount sta wsync beq loop loop2 bit vcount bne loop2 cmp #132 rts Nice work MaPa! Quote Link to comment Share on other sites More sharing options...
Xuel Posted February 18, 2014 Share Posted February 18, 2014 Doh! Never mind. That doesn't work either. It will always report NTSC if you prepend it with "lda:rne VCOUNT". I guess I don't understand how you intended it to work. Quote Link to comment Share on other sites More sharing options...
MaPa Posted February 18, 2014 Share Posted February 18, 2014 (edited) It works for me in emulators (Altirra & Atari800Win), not tested on real HW. It just reads vcount and BIT it with next vcount value. If the next vcount value is zero, then it ends and A holds the last, topmost vcount value in a frame. Edited February 18, 2014 by MaPa Quote Link to comment Share on other sites More sharing options...
Xuel Posted February 18, 2014 Share Posted February 18, 2014 Mapa, I can't get yours to work in either Altirra or Atari800Win. Code and executables below: detect.zip The screen should turn black for PAL and red for NTSC. xuel.xex works, but mapa.xex just goes into an infinite loop and the screen stays blue. Does it work for you? Maybe I made a mistake? 1 Quote Link to comment Share on other sites More sharing options...
Rybags Posted February 18, 2014 Share Posted February 18, 2014 Don't forget the CLI before returning otherwise Stage 2 VBlank continues to be bypassed and most colour changes won't go through. 2 Quote Link to comment Share on other sites More sharing options...
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