May 8: New Mini vMac Development Snapshot

[ClockWise]

Here's the word from the official site:

"Today's Development source snapshot may now work on Raspbian for the Raspberry Pi. (A binary for Linux on ARM is included, stretching a bit the meaning of source snapshot.)

I received a bug report last year that the Linux ARM version of Mini vMac was freezing on the Raspberry Pi. We narrowed it down to a problem with sound, but I couldn't solve the problem without having a Raspberry Pi of my own to work on.

I recently got a Raspberry Pi, and have been able to debug further. As far as I can tell, the "snd_pcm_avail_update" call of ALSA is broken in Raspbian. It doesn't return a value less than the buffer size, but increases without bound. So I've put in a work around, that tests if the result is unreasonable, and if so calls snd_pcm_status_get_avail (after calling snd_pcm_status), which seems to work correctly. (I'm not really sure exactly what the difference is supposed to be between snd_pcm_avail_update and snd_pcm_status_get_avail.) This work around is currently only enabled for ARM.

The work around is actually the second needed fix. The first problem is that before snd_pcm_start is called, snd_pcm_avail_update returns a reasonable looking value, but doesn't change as sound samples are written. Mini vMac was waiting for the ALSA buffer to become full before starting the sound playing, and so sound never started playing. Thinking about it, this algorithm wasn't really right anyway, even if ALSA was working as documented. ALSA doesn't promise that its buffer will be the size you request, it could be much larger or smaller, and so waiting for it to fill could give inconsistent results. So now instead Mini vMac waits until its private buffer is full, then transfers as much as will fit into the ALSA buffer, and then starts sound playing. "

http://minivmac.sourceforge.net/

[adespoton]

I'd really like to see someone build a scale model of a Mac Plus with a Pi inside running mVmac :D

512x342 resolution on a 4" screen! Wire it up to use a real Plus keyboard....