MOD playing on Atari and Amiga

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Re: MOD playing on Atari and Amiga

Postby leonard » Thu Nov 19, 2009 7:56 pm

Zamuel_a wrote:I have never coded anything on the Amiga and wonder how easy the cooper is to use? I think it's rather easy to use Timer B to generate rasters and so on the Atari and it feels like it must be somewhat similar on the Amiga. Ok alittle more code on the Atari, but it feels more like "setup"
If you think about the 13% extra MPU time on the Atari, that gives you around 100 cycles for each visible line on the screen to use with Timer B to get down to the same speed as the Amiga. For just plain rasters you don't use many cycles every line so then the whole machine is still faster than an Amiga.


exept that TimerB interrupt to do raster using CPU and Copper are totally different. Copper is a special custom chip wich can change hardware registers on the fly, without any CPU. Copper can do "color-shock" like effects for free !! Color-shock effect on ATARI takes the complete CPU frame :-(
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Re: MOD playing on Atari and Amiga

Postby Zamuel_a » Thu Nov 19, 2009 8:16 pm

Ok, I have only tried more simple routines there I changed one color each line or a whole palette every 16 line with Timer B. I did play around with rasters 10 years ago, but then I did it in the VBI and synced it to the screen (as with a overscan routine) so I could "draw pixels" on the entire screen with rasters. I made a PONG game for fun that is fullscreen and only uses rasters for graphics. Maybe I should upload it here it anyone is interested :D
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Re: MOD playing on Atari and Amiga

Postby RA_pdx » Sun Nov 22, 2009 9:26 am

Zamuel_a wrote:I made a PONG game for fun that is fullscreen and only uses rasters for graphics. Maybe I should upload it here it anyone is interested :D


Of course, please upload it here! :)
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Re: MOD playing on Atari and Amiga

Postby Zamuel_a » Mon Nov 23, 2009 2:54 pm

Ok, here it is. It was just a fun project I did once then I wanted to play around with rasters. I have tested it on an STE and on STEEM and it worked there so I hope it works on most machines.

It's just good old Pong and since it's 50fps and at a rather low resolution (rasters) it's very fast to.
you control the left paddle with Q and A and the right one with O and L. To Quit, press SPACE.

The raster technic is rather easy. I made a screen buffer so all the drawing is made to that, then I update the rasters everyline with the data from the buffer, and then I had to put the game logic in the NOPs between. I remember it was abit tricky to get the timing ok all the time, but it was easy to see then you were out of sync, then the line got distorted so if I saw that for example half my paddle is a "pixel" to the right, then I used a cycle to much.

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Re: MOD playing on Atari and Amiga

Postby RA_pdx » Wed Nov 25, 2009 9:23 am

Thanks, Zamuel.

Nice idea to do a pong game just with rasters - even it is almost unplayable in the current version.
Maybe you will finish it some day?
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Re: MOD playing on Atari and Amiga

Postby Zamuel_a » Wed Nov 25, 2009 9:51 am

Maybe you will finish it some day?


No I don't think so. It was a long time ago now and it was just a fun project to do anything "useful" with rasters. The speed problem is that the resolution is so small. If it was made with normal graphics the ball could move pixel by pixel in a 320x200 resolution, but here with rasters I'm stucked with 35x27 (I think it was) and the ball will move very fast, or I have to put in a delay between ball movements, but then it would look strange.

Anyway it should be easy to do something else with the raster technic. All rasters are drawn in the "raster_buffer" that is defined at the bottom of the code. Then for every line you can see how it is draw. I even put a comment on every line so you know there you are. There are plenty of unused lines so if you replace the lines at the top there the game code is with some of the unused lines you can do something else.

Actually the resolution is 35*270, but since I wanted it to be "pong pixels" I made it look like there are fewer lines. But stuff like plasma effects and such should be in 35x270 I guess and maybe every odd lines should be a half "pixel" out of phase with the even ones to make it looks better?
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Re: MOD playing on Atari and Amiga

Postby Nyh » Wed Nov 25, 2009 1:27 pm

Zamuel_a wrote:No I don't think so. It was a long time ago now and it was just a fun project to do anything "useful" with rasters. The speed problem is that the resolution is so small. If it was made with normal graphics the ball could move pixel by pixel in a 320x200 resolution, but here with rasters I'm stucked with 35x27 (I think it was) and the ball will move very fast, or I have to put in a delay between ball movements, but then it would look strange.

What you are doing wrong is using move.w (a1)+,(a0) to create the rasters. The right way is to use move.w d0,(a0) and move.w d1,(a0). This way your rasters will be 8 pixels wide (in stead of 12) and you can get a resolution of 52 pixels.

If you are really cool you can use 4 pixel rasters to animate the ball giving you 104 raster pixels. :-)

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Re: MOD playing on Atari and Amiga

Postby Zamuel_a » Wed Nov 25, 2009 4:22 pm

I haven't looked at the code in years and there are probibly many ways to improve it:) A cool thing about rasters are that they are a chuncky "graphic mode" so it should be possible to make some impressive stuff then you don't need the c2p conversion. 8 pixel wide pixels are alittle big, but I guess it's the best you can do. I tried once to use the blitter to draw rasters and I used the halftone pattern to do it. Then I got really small pixels (maybe 4 pixel wide?) but since you have to reload the pattern everytime it was just possible to write 16 pixels (I think i was). The blitter is good then you want to change the entire palette for every line. With the normal movem routine you first have to fill dataregisters with the colorvalues and then use movem again to write it to the palette register. The first movem takes time so I could only change 4 or 5 colors in the palette before the screen started, but with the blitter I could load every register at any time and then at the beginning of the line I made the blit. Then I could change 8 colors in the palette at the beginning of the line.
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Re: MOD playing on Atari and Amiga

Postby Zamuel_a » Thu Nov 26, 2009 3:15 pm

What you are doing wrong is using move.w (a1)+,(a0) to create the rasters. The right way is to use move.w d0,(a0) and move.w d1,(a0).

Hmm. I don't understand? I need to get the pixeldata from A1. If I'm going to use move.w do(a0), then I need to load d0 first. move.w (a1)+,d0 and then move.w d0,(a0) is slower than a move.w (a1)+,(a0)
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Re: MOD playing on Atari and Amiga

Postby Nyh » Thu Nov 26, 2009 4:26 pm

Zamuel_a wrote:
What you are doing wrong is using move.w (a1)+,(a0) to create the rasters. The right way is to use move.w d0,(a0) and move.w d1,(a0).

Hmm. I don't understand? I need to get the pixeldata from A1. If I'm going to use move.w do(a0), then I need to load d0 first. move.w (a1)+,d0 and then move.w d0,(a0) is slower than a move.w (a1)+,(a0)

You pre load D0-D7 with the colors you want to use. An instead of filling A1 with color data you fill it with move.w Dn,(A0) instructions (same number of bytes: 2) and execute the instructions at A1.

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Re: MOD playing on Atari and Amiga

Postby Zamuel_a » Thu Nov 26, 2009 6:12 pm

Ok, but it's hard to fit all the pixels in one line in D0-D7? I can't reload any registers to since that takes time.
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Re: MOD playing on Atari and Amiga

Postby RA_pdx » Thu Nov 26, 2009 6:41 pm

You will need generated code tables to implement Nyh´s idea. Then you can use one of these 8 colours wherever you want. :wink:
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Re: MOD playing on Atari and Amiga

Postby Nyh » Thu Nov 26, 2009 8:40 pm

Zamuel_a wrote:Ok, but it's hard to fit all the pixels in one line in D0-D7? I can't reload any registers to since that takes time.

First you generate the code. In you code you create the rasterfield by filling a buffer with the colors you want to use:

Code: Select all

;draw pad 2
   move.w   #4095,204(a2)      ;16
   move.w   #4095,274(a2)      ;16
   move.w   #4095,344(a2)      ;16
   move.w   #4095,414(a2)      ;16

But what you have to do is, let us assume you fill D0 with $0000 and D1 with $0FFF. Then you draw the pad like this:

Code: Select all

;draw pad 2
   move.w   #$3081,204(a2)      ;16 move.w D1,(A0)
   move.w   #$3081,274(a2)      ;16 move.w D1,(A0)
   move.w   #$3081,344(a2)      ;16 move.w D1,(A0)
   move.w   #$3081,414(a2)      ;16 move.w D1,(A0)

The main field is filled with $3080 (move.w D0,(A0)), giving a black background. Everywhere you want a whithe pixel you insert $3081 (move.w D1,(A0)). The same for all other colors you want to use.

You can end a line with an RTS and play nice tricks with the stack to display the rasters. If you take for the line buffer 64 words then you van do 62 move.w Dn,(A0) instructions + 1 RTS (and one word unused) in one scanline. Taking 8x8 pixel you want to execute every scanline 8 times. So you make as stack that looks like this:
A2,A2,A2,A2,A2,A2,A2,A2+128,A2+128,A2+128,A2+128,A2+128,A2+128,A2+128,A2+128,A2+256,A2+256,A2+256,A2+256, etc, the last entry on the stack has to be the address you want to jump to when you have finished the raster screen. Then you can start drawing the rasters with a jmp (A2) and the whole raster part will be drawn automagicly. Because no interrupts are running you can reuse the whole stack again because the data is not destroyed.

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Re: MOD playing on Atari and Amiga

Postby ljbk » Wed Jun 15, 2011 4:31 pm

Hi !


This thread was very nice to read especially the starting posts.

But let's be serious now that no Amiga owner is reading ... :lol:

STF/STE owners, like myself, can only come close or very close and in some small parts slightly do better, to what i suppose the Amiga Paula chip can do.

From what i understand from the Amiga HW, despite never having have done anything on it, here is what Paula can do:

1- Paula receives a master clock that is derived from the CPU clock;
2- That clock will be the input controlling the four "frequency" dividers;
3- Each time that divider reaches 0, a 8 bit sample byte is fetched from the sample buffer;
4- That value is multiplied by the data inside the voice volume register leading to a 14 bit value stored for that voice, so Paula should have 4 registers of 14 bits;
5- The stereo mixing adds two of these to each other leading to two 15 bit values for left and right speakers;
6- The 15 bit values go through 15 bit DACs to be converted into analog electric signals at a rate of 28 KHz (56 KHz for A1200);
7- Those electrical signals go through the filter that might be active or not before reaching the speakers;


What are the problems to do this with STF/STE:

- The frequency/tone playing will NEVER be as precise as dedicated hardware but it can come very close depending on the mixing rate;
- The "volumed" data is normally never as precise as 14 bits on the STF/STE players (for example with Lance's 4 voices routines, the sample data is reduced and volumed to 7 bit to simplify the adding: 7bit + 7bit = 8 bit) but it can come close ...;
- The STE DACs are only a 8 bit ones but they can work at 50 KHz and a software amplification can be done like in Hextracker;
- On STF there is no DAC so your YM2149/DAC table has to be good;
- There is no filter on STF/STE;


In conlusion, the two situations are not comparable. While the Amiga users have the HW on their side to help them, STF/STE users have to use their head, and a vast amount of their CPU power, to reach a very similar quality.




Cheers,
Paulo.

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Re: MOD playing on Atari and Amiga

Postby Cyprian » Wed Jun 15, 2011 8:00 pm

sometimes ago I heard that Lance player somehow manipulates LMC 1992 for improve sound quality.
There is 20 levels (~4bits) for left / right chanels and 40 (~5 bits) for master volume.
8bit sound plus 4 or 5 additional bits sounds very interesting.
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Re: MOD playing on Atari and Amiga

Postby EvilFranky » Wed Jun 15, 2011 9:29 pm

Hmm, well I have heard some things about Amiga being able to mix down the 4 channels to get 2 14 bit channels, but due to DMA limits (or something like that) they are unable to get replay higher than 28khz.

I don't know the full ins and outs, but hearing a MOD at 50khz on an STE has always sounded better to me than the same MOD on an Amiga. Its been a long time though and have no access to an Amiga, only an STE and Falcon.

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Re: MOD playing on Atari and Amiga

Postby ljbk » Thu Jun 16, 2011 12:22 am

Cyprian_K wrote:sometimes ago I heard that Lance player somehow manipulates LMC 1992 for improve sound quality.
There is 20 levels (~4bits) for left / right chanels and 40 (~5 bits) for master volume.
8bit sound plus 4 or 5 additional bits sounds very interesting.


The registers you refer are the Microwire ones that apply to the real output voices and not to the virtual voices.
When you play a MOD on STE, you have 4 virtual voices that are mixed on 2 real voices (in case of stereo) or on one real voice (in case of mono).
If you play around with the Microwire registers in case of stereo to change the master volume, right volume, left volume, treble, bass and mixer, you will change the way the mod is to be played.
That's easy: in a 4 voice mod you can have 4 different volumes at once an you have nowhere no set them or you have to compromise like Octamed does on Amiga squeezing 8 volumes in 4 hardware registers.
So the result resolution is only 8 bits.

Regarding Lance routine, you just need to read his source available with Oktalyser STE. There it is obvious that the mixing is done in the way i explained:
- 4 voices = 2 mixings of 2 voices where each one is limited to 7 bits: 7bit + 7bit = 8bit;
- 8 voices = 2 mixings of 4 voices where each one is limited to 6 bits: 6bit + 6bit + 6bit + 6bit = 8bit;

PS/EDIT:
There is a use of the Microwire chip in Lance's routine but not for the master volume as far as i can understand his code.
Left and Right volume are set to the max volume of the 2 mixed voices and so you only have to pass one of the two mixed samples through the volume table conversion with the volume value adapted to the maximum value of the other voice. As an example, if you mix a voice with volume 48 and another voice with volume 12, then you can set the real voice in LCM taken from the table below for 48 and copy the sample bytes unchanged and for the second voice you pass the bytes through a volume table for level (12/48)*64(or volume table max) = 16. For the other stereo channel, you just have to do the same with a different LCm volume and adapted volume to select the correct volume table.
But unfortunatly the LCM volume control is not very precise and so a 0 to 64 volume is converted in a much less accurate volume for LCM: a little more than 3 bits. This is nowhere as precise as going via a volume table but of course it is faster. Here is a part of his source to prove it:
"
.mt_LCM_vol_tab dc.w 0
dc.w 2,5,7,8,9,10,10,11,11,12,12,13,13,13,14,14
dc.w 14,14,15,15,15,15,16,16,16,16,16,16,17,17,17,17
dc.w 17,17,17,18,18,18,18,18,18,18,18,18,18,19,19,19
dc.w 19,19,19,19,19,19,19,19,19,20,20,20,20,20,20,20
"


EvilFranky wrote:Hmm, well I have heard some things about Amiga being able to mix down the 4 channels to get 2 14 bit channels, but due to DMA limits (or something like that) they are unable to get replay higher than 28khz.

I don't know the full ins and outs, but hearing a MOD at 50khz on an STE has always sounded better to me than the same MOD on an Amiga. Its been a long time though and have no access to an Amiga, only an STE and Falcon.

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The Amiga (A500 and A1200) can play 4 voices with something like a 14 bit resolution each but with no volume control.
This is achieved by setting each voice volume register for each sample byte read at the same pace the DMA is reading thata data. As the volume register contains a value from 0 to 64, the resulting multiplication to a 8 bit sample data is a value from 0 to 255*64= $3FC0. The combinations obtained by this multiplication cover many/most of the 14 bit values. but they are not equally distributed. It is a bit like saying that the 3 PSG registers with 4bits can do the complete set of 12 bit values with a main difference in the non-linearity of the PSG levels.
Anyway, that Amiga trick will produce many levels close to the middle, some of them with several combinations, and less levels to the extremes.

Here are examples:

1- several combinations
- level 1024 can be obtained with a 64 sample level and a 16 volume;
- same level can be obtained with a 32 sample level and a 32 volume;
- same level can be obtained with a 16 sample level and a 64 volume;

2- no combination
- levels(signed) $1FC1..$1FFF can not obtained;
- level $1FC0 is obtained with sample 127 and volume 64;
- levels(signed) $1F81..$1FBF can not obtained;
- level $1F80 is obtained with sample 126 and volume 64;
- levels(signed) $1F42..$1F7F can not obtained;
- level $1F41 is obtained with sample 127 and volume 63;
- level $1F40 is obtained with sample 125 and volume 64;
...

The following GFA program can do the calculations for the positive half:

Dim a%(8193)
for i%=0 to 64
for j%=0 to 128
a%(i%*j%) = 1
next j%
next i%
result_sum% = 0
result_interval_sum%= 0
previous% = 0
for i%=1 to 8192
if a%(i%) = 1 then
add result_sum%,1
add result_interval_sum%, i% - previous%
previous% = i%
endif
next i%
print result_sum%, result_interval_sum% / result_sum%

The result obtained is 3006 different combinations with an average interval of 2.7252 units.
Joining the 2 halves (positive and negative) we have around 6000 different combinations possible and so we have a real 12.5 bits (log 6000 / log 2) resolution on a 14 bits space.
Close to the 0 line, all combinations are possible so we have the real 14 bit precision but next to the highest or lowest possible value for the last case we are down to 8 bit precision, so one could also consider an average of (14+8)/2 = 11 bits.
That is why i wrote above: " something like a 14 bit resolution " ... :wink:


The A500 can only produce a 28 KHz output signal with normal video mode because of the related DMA channels time slots. The A1200 can do 56 KHz.


Cheers,
Paulo.

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Re: MOD playing on Atari and Amiga

Postby abraxxious » Fri Mar 06, 2015 2:36 am

Not quite sure why you think the Amiga can only play back at 28 khz, but it can actually play back at 56 khz (interleave mode) - higher than the STe and the Amiga's Paula sound system supports variable playback sample rate, the STe only supports a few fixed rates. This makes playing samples as instrument voices MUCH easier on the Amiga.

Zamuel_a wrote:Every Amiga owners always says that the Amiga is best on playing tracker music and ok, it got 4 channels, BUT the Atari has a higher processor speed so I wonder how much the difference are? The Amiga can only play in 28kHz to, while the STE can do it in 50.
I know the Lance tracker can play 50kHz mods in about 30% processor time, so shouldn't a 25kHz (which is similar to Amigas 28kHz) be able to run in maybe 20% processor time? And the Atari is about 13% faster so maybe it can compensate for the lack of 4 channel output? Atleast it sounds to me that the difference isn't so big as many people thinks, and I prefer to listen to 50khz mods if I can choose :)

A Amiga mod player routine must take some time to? There is alot more than just output audio data in a mod player so it must take some time there to.

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Re: MOD playing on Atari and Amiga

Postby Zamuel_a » Fri Mar 06, 2015 6:42 am

It is from a technical desciption I found regarding the Amiga sound. The disscusion is for an Amiga 500 with a PAL or NTSC monitor.

memory access is prioritized and one DMA slot per scan line is available for each of the four sound channels. On a regular NTSC or PAL display, DMA audio playback is limited to a maximum output rate of 28867 values per channel (PAL: 28837)
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Re: MOD playing on Atari and Amiga

Postby Frank B » Fri Mar 06, 2015 9:17 am

abraxxious wrote:Not quite sure why you think the Amiga can only play back at 28 khz, but it can actually play back at 56 khz (interleave mode) - higher than the STe and the Amiga's Paula sound system supports variable playback sample rate, the STe only supports a few fixed rates. This makes playing samples as instrument voices MUCH easier on the Amiga.



Yes. But only if you use a VGA style monitor. That's a bug not a feature btw!

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Re: MOD playing on Atari and Amiga

Postby Zamuel_a » Fri Mar 06, 2015 10:09 am

Yes. But only if you use a VGA style monitor. That's a bug not a feature btw!


Can you use a VGA monitor for Amiga 500 or is it only for the higher end versions?
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Re: MOD playing on Atari and Amiga

Postby Frank B » Fri Mar 06, 2015 10:18 am

Zamuel_a wrote:
Yes. But only if you use a VGA style monitor. That's a bug not a feature btw!


Can you use a VGA monitor for Amiga 500 or is it only for the higher end versions?


You need ECS at a minimum. So from a 500+ I think. In ECS VGA support is a bit limited. 4 colours from a 64 colour palette.

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Re: MOD playing on Atari and Amiga

Postby ctirad » Fri Mar 06, 2015 10:50 am

The ECS chipset was in A500+, A600, A3000 and latast revision of the A500, what was basically the A500+ board with only half of the RAM fitted and ROM 1.3.

However, this new mode was never marketed as VGA althrough is somewhat VGA compatible. It was called "productivity" and it was a try to add an ergonomic resolution like ST-High for production purposes. The mode(s) is derived from the 15KHz PAL/NTSC ones, just with doubled horizontal frequency. The pixel clock is still th eoriginal 28MHz. Its byproduct was the superhires mode with 1280 pixels per line (15Khz only).

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Re: MOD playing on Atari and Amiga

Postby Frank B » Fri Mar 06, 2015 11:53 am

ctirad wrote:The ECS chipset was in A500+, A600, A3000 and latast revision of the A500, what was basically the A500+ board with only half of the RAM fitted and ROM 1.3.

However, this new mode was never marketed as VGA althrough is somewhat VGA compatible. It was called "productivity" and it was a try to add an ergonomic resolution like ST-High for production purposes. The mode(s) is derived from the 15KHz PAL/NTSC ones, just with doubled horizontal frequency. The pixel clock is still th eoriginal 28MHz. Its byproduct was the superhires mode with 1280 pixels per line (15Khz only).


I'm not sure the ECS chipset was released in full on the 500. The updated Agnus yes but not Denise. I've never seen a 500 with the full ECS in it.

ctirad
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Re: MOD playing on Atari and Amiga

Postby ctirad » Fri Mar 06, 2015 12:09 pm

I'm absloutely sure it was. I bought my A500 in 1991 and I had A500 board with 1MB Fat Agnus inside. A friend of me bought his A500 a copule of moths later in the same shop and had A500+ motherboard inside. He later upgraded the machine to a full A500+ just by adding four missing RAM chips and replaced ROM. Perhaps there was also some missing 74xx chip near the trapdoor connector needed for further 2MB upgrade.


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