--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/compal/audio/tfc139-headset-entry	Sat Oct 09 23:20:00 2021 +0000
@@ -0,0 +1,49 @@
+The following results have been obtained by connecting to a C139 phone via the
+headset jack, switching to "Trace On" via the **16379# hidden menu, breaking in
+with tfc139, then running the new tfc139-audio-dump command in fc-loadtool:
+
+d_aec_ctrl: 0x03C7
+New AEC params: 0x0001 0x0014 0x4CCC 0x59AD 0x7500 0x0000 0x1000 0x1000
+
+Uplink FIR coefficients:
+
+0x4000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000
+0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000
+0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000
+0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000
+
+Downlink FIR coefficients:
+
+0x7FFF 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000
+0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000
+0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000
+0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000
+
+VBCTRL1: 0x004
+VBCTRL2: 0x007
+VBPOP:   0x004
+VBUCTRL: 0x1B2
+VBDCTRL: 0x069
+
+Commentary: the values read out of VBCTRL1 and VBCTRL2 registers are consistent
+with the headset audio channel being selected for both input and output, leading
+to the suspicion that the firmware probably switched the audio path to headset
+mode even though the **16379# hidden menu selection was set to "Trace On".  The
+Mother's primary interest here is to see the official C139 fw settings for the
+handheld audio mode (built-in earpiece and mic) rather than the headset mode,
+but it now appears that such capture won't be possible except maybe by
+connecting to the production test pads inside the battery compartment,
+bypassing the headset jack.
+
+Looking at what appears to be C139 headset mode audio config, we see that
+HSMICBIAS voltage is set to 2.0 V, the uplink gain is set to 8 dB, and the
+sidetone level is set to -23 dB: we get this info from the MICBIAS bit in
+VBCTRL1 and the VBUCTRL setting.  Decoding VBDCTRL, we see that the volume
+control is set to -6 dB and the PGA gain is set to 3 dB.  However, these
+VBDCTRL settings don't tell us much: see the volume-ctrl article.
+
+Also note the FIR coefficient oddity: no frequency curve-transforming FIR
+filters are being set up, neither UL nor DL, but DL FIR coefficient 0 is set to
+0x7FFF instead of 0x4000.  This oddity means that Calypso DL FIR block is
+producing a 6 dB gain (doubling of the samples) purely on the digital side,
+before DL audio passes to the ABB - certainly a noteworthy hack.