Subject: Re: LoFI (DEcaudio) documentation?
To: Aaron J. Grier <firstname.lastname@example.org>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
Date: 06/18/1998 12:12:52
>RE: multiple /dev entries for LoFi
>> What's the best way to do this?
>I think a lot of it depends on whether or not multiple channels on
>the LoFi can be accessed at the same time,
>From skimming the docs, I think they can.
It's not just that there are several channels. There are three
independent devices: two independent am79c30s (one for telephony/ISDN,
one for audio) plus whatever is on the DSP's serial port (builtin
stereo DAC, or a NeXT-compatible external device using the DB-15
connector to the DSP serial port).
The LoFi card is PIO-driven (host CPU copies to/from onboard SRAM) and
the DSP handles all the accesses to onboard SRAM via the host CPU
(i.e., DSP copies to/from onboard SRAM and device). The TR suggests
synching frames on the two CODECs and servicing both from a single DSP
interrupt. So those can definitely be driven in parallel. If the DSP
has enough oomph, interrupt-driven code to shift data to the stereo
DAC via the DSP serial port would work too.
> and whether or not NetBSD
>supports multiple readers/writers to the same /dev entry.
The sparc port doesn't. The ISA drivers I've looked at don't. And
I'd want the driver to restrict access to one reader/writer per
independent hardware device. I'd guess the userlevel software expects
EBUSY at open time, not when selecting a channel.
>It would be
>really clever if the DSP code could be cooked up to do automatic mixing
>of multiple writers to /dev/audio. :)
Yes, it would, but I'm not going to cut the DSP code to do it :->.
>BTW -- does anybody know the DEC part number for the LoFi DB60 cable?
>I've got a LoFi card and breakout box with power supply, but no cable. :(
Dunno. looks like a straight-through DB-60 to me.