Bluetooth audio on embedded hardware

I would really like the bluetooth-alsa project to get far enough along to really shine on embedded platforms. gumstix is the perfect little device for working this out.

Completed items

Modify btsco to build in a cross-compile buildroot environment (seems to have broken again in 2.6.14 buildroot)
Tweak build so kernel module snd-hwdep-new gets built (need to make sure it gets installed automatically)
Figure out hcid.conf settings and required modules for audio
Fix timing problem in a2play--setitimer and rtc/pthreads timers
Implemented unrolled and fixed-point a2dp encoder and fixed-point decoder
Implemented 32-bit fixed point codec, made it the default fixed point, moving it into its own independent library

Status

Stereo A2DP transmission (.au file) with a2play: audio breaks up occasionally but comes back (using -n flag)
Live stereo transmission from line-in: occasional bursts of static (probably endian problems again)
Stereo reception with a2recv: cpu is working hard and audio is working using subbands=4,blocks=4,bitpool=12 (should work with any settings now that decoder is in fixed-point)
SCO (voice-quality audio) with btsco: gumstix connects to bluetooth headset and responds to headset controls but audio is not going through
Some basic AVRCP code; able to receive commands in a separate process

To-do

fix btsco.mk for 2.6.14+ buildroot
Squash the last remaining quality problems with fixed point encoding (high frequencies are distorted) and retire floating point :)
Set up AVRCP to control the stream
Find out if future gumstix boards could have PCM pins from infineon connected to xscale (yes! confirmed!)
Find out if SCO can be mapped to HCI as it can on CSR (maybe; see bluez-devel topic "SCO over UART")
Try connecting a CSR bluetooth chip to see if audio works better (see next section)

Bluetooth 1.1 CSR Module

The avantwave class 1 module is here. The specs are here and the specific model is btr140-h4-921k. Now I need to connect it up. I'm going to get access to hirose pins through the tweener vias (tweener also has a 3.3v converter which might be usable when I try a class 2 module) hciattach times out complaining about no connection. I have a newer module so I'm likely to spend additional effort getting it to work.

BTR140 hirose pxa Description
1 - attached an mmcx post here for an external antenna
5 14 gpio35 steal GPIO from ffuart for btr140 active high reset
7 32 gpio50 module uart rts->hwcts (asserted by module)
8 34 gpio51 module uart cts<-hwrts (asserted by gumstix)
9 33 gpio49 module uart tx->hwrxd (asserted by module)
10 35 gpio48 module uart rx<-hwtxd (asserted by gumstix)
15 - 1.8v using a voltage regulator (digikey MCP1700-1802E/TO-ND or NJM2845DL118TE1CT-ND) for a max 161mA
6,16 30 3.3v using voltage regulator for max 161mA
17 1 Ground
11 3.3v synchronous serial (active low) do we use synchronous??
18 pcm clock
24 gnd (dual boot fn)
25 pcm out
26 pcm in
27 pcm sync
42 - rf ground (also surrounds pin 1)

BTR140	hirose	pxa	Description
1	-		attached an mmcx post here for an external antenna
5	14	gpio35	steal GPIO from ffuart for btr140 active high reset
7	32	gpio50	module uart rts->hwcts (asserted by module)
8	34	gpio51	module uart cts<-hwrts (asserted by gumstix)
9	33	gpio49	module uart tx->hwrxd (asserted by module)
10	35	gpio48	module uart rx<-hwtxd (asserted by gumstix)
15	-		1.8v using a voltage regulator (digikey MCP1700-1802E/TO-ND or NJM2845DL118TE1CT-ND) for a max 161mA
6,16	30		3.3v using voltage regulator for max 161mA
17	1		Ground
11	3.3v		synchronous serial (active low) do we use synchronous??
18			pcm clock
24			gnd (dual boot fn)
25			pcm out
26			pcm in
27			pcm sync
42	-		rf ground (also surrounds pin 1)

Notes

PSKEY_HOST_INTERFACE values are 1 (BCSP), 2 (USB), 3 (H4) so I thought we need 3. In the end it was unnecessary to change this.

PSKEY_INITIAL_BOOTMODE (x3cd) should be 4 for HCI H4. It's shipped set to 3 for USB.

PSKEY_UART_BAUDRATE (x1be) should be x1d8 for 115k or xebf for 921k. The default was 115k so I left it alone.

It seems that PSKEY_HOSTIO_MAP_SCO_PCM (x1ab) should be 0, equivalent to the old "pskey mapsco 0" command. There is no x1ab key and hciconfig hci0 revision indicates SCO mapping: HCI so HCI must be the default routing.