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comparison compal/audio/omr-via-headset @ 380:a66cb88c5f77

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compal/audio/omr-via-headset: result of experiment
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 10 Oct 2021 21:48:24 +0000
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379:a760a5eeed65 380:a66cb88c5f77
1 Follow-up on the experiments described in the omr-guide article: I connected
2 the headset jack serial cable to a C139 phone that has a SIM inserted, and
3 booted it up with a real GSM network connection. And then I made a test call.
4 There is a headset icon displayed on the home screen, and no sounds emanate
5 from the built-in earpiece speaker, so it is definitely in headset mode.
6
7 However, by getting into the active call state, I was able to access the volume
8 control screen, and I got an omr reading of d_vbdctrl DSP API word at each
9 volume level. Here they are:
10
11 Level d_vbdctrl VBDCTRL Vol gain PGA gain Total
12 ------------------------------------------------------------------------------
13 0 0x018C 0x006 -12 dB 0 dB -12 dB
14 1 0x020C 0x008 -12 dB 2 dB -10 dB
15 2 0x028C 0x00A -12 dB 4 dB -8 dB
16 3 0x030C 0x00C -12 dB 6 dB -6 dB
17 4 0x1A4C 0x069 -6 dB 3 dB -3 dB
18 5 0x1ACC 0x06B -6 dB 5 dB -1 dB
19 6 0x09CC 0x027 0 dB 1 dB 1 dB
20 7 0x0A8C 0x02A 0 dB 4 dB 4 dB
21
22 Additional observation: the volume levels listed above exist only in the active
23 call state: when a call ends, the fw switches to fixed level 4 for keybeeps and
24 whatnot. When a new call begins, the fw restores the last set in-call volume
25 level.
26
27 Further observation: DL FIR coefficients stay the same at all 8 volume levels:
28 0x7FFF in coefficient 0, zeros in all others. Thus Compal's hack of adding
29 another 6 dB of gain via the FIR block is unaffected by volume control, and no
30 frequency curve transformation is ever applied, at least in headset mode.
31
32 Regarding AEC: the reading of 0x03C7 from d_aec_ctrl when breaking in with
33 tfc139 definitely seemed suspicious. Reading the same word via omr, we get
34 0x0226 while in an active call and 0x03A7 after the call ends. Furthermore, we
35 can catch a little bit of trace output related to headset insertion if we have
36 rvinterf running and do the **16379# trace enable step before inserting the
37 serial cable into the headset jack, and we see this trace message:
38
39 L1: AEC_R <fn> 03a6 0001 0014 4ccc 59ad 7500 0000 1000 1000
40
41 Thus it looks like C139 headset mode AEC configuration is:
42
43 * AEC enabled (bit 1 in d_aec_ctrl)
44 * noise suppression enabled (bit 2 in d_aec_ctrl)
45 * NS level bits (d_aec_ctrl[6:5]) are set to 0x20
46 * New AEC parameter words are 0001 0014 4ccc 59ad 7500 0000 1000 1000
47
48 VBC registers during active call:
49
50 Register DSP API word 10-bit register value
51 -----------------------------------------------------
52 VBCTRL1 0x0110 0x004
53 VBCTRL2 0x01D6 0x007
54 VBUCTRL 0x6CCE 0x1B3
55
56 Notice VBUCTRL diff: we read 0x1B3 (9 dB uplink gain) when we are in an active
57 call, but 0x1B2 (8 dB uplink gain) otherwise.