--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/compal/audio/volume-ctrl	Sat Oct 09 23:20:00 2021 +0000
@@ -0,0 +1,20 @@
+It appears that the only way to bring up audio volume control (as opposed to
+ringer volume) on a C139 phone running Mot official fw is to be in active call,
+implying the need for a valid SIM, a GSM network, working service with that
+SIM+network combination and a party one can test-call.  When you do get into
+the necessary active call state, navigation left and right buttons bring up the
+audio volume control screen and move this volume up or down.  However, instead
+of seeing just 5 possible volume levels as would be available if Iota ABB
+downlink volume controls were used in TI's simple way, we see 8 possible volume
+levels being offered by Motorola's fw, numbered from 0 through 7.  Level 0 is
+not mute - downlink audio is still present in the earpiece speaker, albeit
+quiet.
+
+It appears that Compal did something similar to Foxconn/Pirelli, probably
+manipulating both volume and PGA gain settings in Iota VBDCTRL in order to
+offer more than 5 possible volume levels to the user.  However, because Compal
+firmwares don't have ETM and their oabbr TM3 command is broken (returns
+garbage), we don't have a way to just read out the register settings for each
+volume level.  Furthermore, because the audio volume setting is so difficult to
+get to (requiring not only a SIM, but also network registration and a call),
+doing a tfc139 break-in for each possible volume level would be too much work.