MP3@64 stuttering and skipping

[Daedalus]

Sorry, bit late onto this thread, but can any of you confirm that you're using the MP3@64 off the internal clockport on an A1200? And if so, how did you achieve this? Using a clockport riser I guess? Also, how is performance? Like, what's the highest bitrate you can play on your machine and with what software?

I'm currently using a MAS player for an ongoing MP3 jukebox project, and I might consider going the MP3@64 route if it's less CPU hungry than the current parallel port transfers...

[Daedalus]

The only CPU power I can imagine is used in MAS is accessing an IDE hard drive. If you have a DMA capable hard drive then it should be very little.

The same overhead will be present if you switched to MP3@64

Well, I'm trying to keep to as little additional hardware as possible, so it's a bog standard A1200 with an 030/16 and a hard drive at the moment and little else. Surprisingly, the MAS does use a bit of CPU power, and I guess uses a lot of interrupts for its tight timing. It uses the parallel port, but not in parallel, if you get me - all the data has to be converted in software to serial for the I2C bus that the MAS chip requires. If the MP3@64 didn't need to do that conversion, it should be easier on a little machine like mine...

Especially since I'm writing the software and it's not exactly efficient

[Daedalus]

Thanks for that! Yeah, it's the stuttering I'm worried about - I was thinking it could be a factor of DMA timing or something which affects certain A1200 motherboards. The MAS Player uses the same decoding chip as the MP3@64, but like I said in my previous post, just takes a little bit of CPU power to do a serialisation of the data before sending it out the parallel port. It's a shame there's nobody living nearby I could borrow one from to test it

[Daedalus]

Yeah, there are known issues - and sometimes they only show up for other hardware, so it's possible that the machine is unmodified and works fine without anything on the clock port, but putting something there upsets it. Since I'm running an 030 it may well be better.

BTW, the network card issue is known and there's a software fix for it, should you want to try it again. Worst case scenario, it can be hot unplugged and plugged back in to reset it manually...

[Daedalus]

Yeah, you probably could pre-process them, but that low level of stuff is kinda beyond me - once you start that you can't use the MHI driver and have to do all the timing and interrupts yourself, and I wanted it to be able to accept standard MP3 files from CF cards etc.

The parallel port itself is able to do it speed-wise for 192kbps files anyway, I don't have any trouble with that here. Possibly something to do with the clever trick the player does in clocking data on the leading and falling edge of the signal, thus saving half the number of pulses...

[Daedalus]

Thank you Chris for that good, concise explanation. It seems that there wouldn't be much benefit for me to switch to the MP3@64. Do you know why the interrupt isn't used? Or if it might be possible to modify the MP3@64 or the MAS player to use it? I guess then it would also need a new MHI library...

I am hoping to be able to use the internal serial port with my project, but it can be run at low speed (9.6k should be enough) as it's only used to update an LCD display and maybe receive IR remote codes in the future, so I don't think the interrupt load will be too high. If it is, do you think that could be improved by switching to the MP3@64?

[Daedalus]

@AmigaNut08

Ouch! Yeah, the clockport (and its clones) have access to the +5V line which is only restricted by what the traces can carry, so it's very easy to burn things out! Does the Buddha card not have a mark showing which end is pin 1? Even this howevr isn't a good indication... From the Amiga Hardware Database:

- when installed in Zorro slot, pin 40 of the card's clock port is towards the front side of the computer, pin 19 resp. pin 1 towards the rear side

- marked wire of clock port expansions go to pin 19 or pin 40, depending on the manufacturer's definition - e.g. expansions made by Individual Computers are installed with the red stripe on pin 40 (to the left), expansions of E3B mark pin 19 / pin 1 (to the right)

Having the floppy connector plugged in wouldn't have caused this, but it might have prevented damage to the motherboard/Buddha card by not pulling all that power through them - depending on their design of course.