SoundDMA randomly crashes on the Pi1

I’ve been seeing random SoundDMA crashes and tracked it down to Sound0HAL using R14 whilst in IRQ32 mode. It looks like this issue has been there since Sound0HAL was originally created.

Various lines of the 8bit to 16bit conversion code, such as line 3394 reference R14 whilst in IRQ mode and run the risk of R14 becoming corrupt if an IRQ occurs – which is what I’m seeing.

Can the code be modified to use a different register, or use the original Sound0 method:

LDR     r0, =SoundLevel0Base    ; address our local data
LDR     r0, [r0, #SoundRMA]     ; go get RMA space address

EDIT: It looks like IRQ’s should be off around the code, as line 3334 is disabling them before calling level 1. Perhaps line 3361 should ensure IRQ are off on the return before restoring R14?

MSR     CPSR_c, #I32_bit + IRQ32_mode ; IRQs off again
LDMFD   sp, {r4,r6,r10,r12,r14} ; restore saved values. NB leave on stack: no `!'

This stuff used to be my bread and butter, but I’m so rusty it’d use my entire stock of wet-and-dry to get back up to speed. I hope someone else is on the ball! 8~)

Perhaps line 3361 should ensure IRQ are off on the return before restoring R14?

Yeah, that sounds reasonable. Really it’s a bug in the level 1 code if it’s returning with IRQs enabled (although I haven’t checked what the PRMs say). But since it’s only one extra instruction there’s no harm in building some protection into the OS.

Looking at the IOMD version of SoundDMA, it looks like it assumes that the level 1 code (and anything else) will be preserving the IRQ state, but it doesn’t do anything critical with R14 and so it won’t suffer a catastrophic failure if one of the routines returns with IRQs enabled.

FYI – This should be fixed as of a week or two ago (SoundDMA HAL 1.84, and SoundDMA AC97 (i.e. Iyonix version) 1.69)

Jon: did it error or just fall silent?
I wonder if this might also fix sound going silent for some people!

It randomly crashed the machine as Sound0HAL now makes use of R14.

I’ve not heard of it going silent before. One thing to try in that scenario is RMReInit all the relevant sound stack Modules, to see if it’s software or hardware related. IIRC, the order is:

RMReInit SoundDMA
RMReInit SoundChannels
RMReInit WaveSynth
ChannelVoice 1 1
CTRL-G

I have reported before about DigitalCD going silent when writing a full display to my OLED. Not bothered to look at why, beyond “disables interrupts for too long”.