CIA or vertical blank/copper interrupt for playing music in an intro?

[DanScott]

I mean that it doesn't use a copper interrupt at all.

The music player is called at the top of the vblank interrupt, and then in the copperlist, there's a copper wait for (for example) line 15 followed by a copper move to DMACON.

The music player just patches this copper move with the correct value, and it is automatically set by the copper at line 15

[phx]

Originally Posted by DanScott

The music player is called at the top of the vblank interrupt, and then in the copperlist, there's a copper wait for (for example) line 15 followed by a copper move to DMACON.

Ah, sorry, I read too fast and wanted to see INTREQ instead of DMACON.

The music player just patches this copper move with the correct value, and it is automatically set by the copper at line 15

That's smart and is probably the best solution for a VERTB-based player. The same is done for writing the repeat-pointers to AUDxLC, a few lines later?

[DanScott]

Originally Posted by phx

Ah, sorry, I read too fast and wanted to see INTREQ instead of DMACON.

That's smart and is probably the best solution for a VERTB-based player. The same is done for writing the repeat-pointers to AUDxLC, a few lines later?

I don't think that's necessary with LSP... but I guess it could work for a player that needs to set AUDxLC too. Removes a lot of overhead cycles "wasted" by interrupt handlers and CPU internal interrupt triggering

[a/b]

Originally Posted by phx

That's smart and is probably the best solution for a VERTB-based player. The same is done for writing the repeat-pointers to AUDxLC, a few lines later?

There are two modes for that (neither involves copper):
1. no short samples, they are set at the start of the next frame (with a ~20ms delay but that's ok because samples are sufficiently long and haven't started looping yet)
2. short samples, the usual cia timer method

[koobo]

Originally Posted by Antiriad_UK

As others said use PHX's routine for most cases. I use in my intros too.

For scenario above. Cia interrupt for music players is level6 (high priority) and usually only takes a few scan lines to execute. Because of the module timing it will generally occur at a different scan line each frame. For example on frame 1 the cia interrupt may be around scanline 10, on frame 2 it may be 30, basically it could happen anywhere. (Interesting to watch it move around with WinUAE visual debugger)

If you are triggering a lev3 interrupt with the copper alongside PHX's player with cia interrupt then usually will have two outcomes:
1. Lev 6 CIA interrupt is currently executing when copper requests lev3 interrupt
- Lev3 interrupt can't interrupt lev6, so lev3 interrupt only starts once lev6 interrupt finished

2. Lev 3 interrupt is currently executing, cia lev6 requested
- Lev6 cia CAN interrupt lev3, once lev6 finished continues with lev3

So yes, you have to think a little bit about some scenarios where this could cause an issue. For example if you have a very precise "wait for line x" with the cpu in a lev3 then it could potentially miss that check periodically if the music player happened at the same time. So often safer to "wait for line greater than". In practice it's usually fine and you just start the music playing and forget about it

An anecdote in system programming, ie. non-demo context. Using a level 6 CIA-timer for module playback will disturb serial transfers which use the level 5 interrupt. Therefore HippoPlayer triggered a level 1 interrupt for music playback from which ever CIA-timer it was able to allocate.

Out of four available CIA-timers two trigger lev2 and two trigger lev6 interrupts. Lev2 timer interrupt and lev1 software interrupt are available in demo programming as well.

All of the above with the "as far as I can remember" -disclaimer

[meynaf]

Originally Posted by koobo

An anecdote in system programming, ie. non-demo context. Using a level 6 CIA-timer for module playback will disturb serial transfers which use the level 5 interrupt. Therefore HippoPlayer triggered a level 1 interrupt for music playback from which ever CIA-timer it was able to allocate.

Out of four available CIA-timers two trigger lev2 and two trigger lev6 interrupts. Lev2 timer interrupt and lev1 software interrupt are available in demo programming as well.

All of the above with the "as far as I can remember" -disclaimer

I second that.
DeliTracker does the same : trigger a SoftInt to defer the work so that the player does not disturb anyone.

Also, as mentioned CIA-B has high priority but CIA-A is lower than Copper and Vert Beam.

But there is another way to handle this. Let's say your main interrupt has to do heavy duty stuff but also some small but more time critical things.
You could separate the two by triggering another lower priority interrupt, but you also have the possibility to reallow interrupts by setting an appropriate IPL level in SR and tell Paula you're done with your high level interrupt (by simply acknowledging it before it has finished).
Then, start with the fast but time critical stuff, then reallow interrupts (including lower level ones), then do the more heavy duty things (which are ok to interrupt with a module player).
(Not sure i've been clear on this ).