# HG changeset patch
# User Mychaela Falconia <falcon@freecalypso.org>
# Date 1625342002 0
# Node ID c6dafe9f3ac2128db75c7b5fd2cabd632b7c3ebd
# Parent  bdc5d8d9fa1fec711730c2a42127f570c6d4cb1b
FC-handset-spec: BCI header change on Venus

diff -r bdc5d8d9fa1f -r c6dafe9f3ac2 FC-handset-spec
--- a/FC-handset-spec	Sat Jul 03 18:10:56 2021 +0000
+++ b/FC-handset-spec	Sat Jul 03 19:53:22 2021 +0000
@@ -1370,8 +1370,15 @@
 for exercising the charging boot path in particular, Iota VCHG needs to be
 brought out like it is on iWOW DSK and FC Caramel2 boards, to be connected with
 a jumper wire to +5V pin on the DUART28 USB adapter whenever a "charger plugged"
-condition needs to be presented to the chipset.  FC Venus will feature a 2x4 pin
-header with Iota BCI signals like on Caramel2:
+condition needs to be presented to the chipset.  FC Venus will feature a 2x3 pin
+header with Iota BCI signals as follows:
+
+VBATS	VCCS
+PCHG	VCHG
+ICTL	GND
+
+Please note that this planned BCI header pinout differs from iWOW DSK and FC
+Caramel2, which implement the following 2x4 pinout instead:
 
 ICTL	VCCS
 PCHG	VCHG
@@ -1385,7 +1392,30 @@
 connect an actual battery and an actual Iota-controlled charging circuit, it
 will be possible: the battery will need to be connected to the orange power
 input connector, and the control signals for the charging circuit will need to
-be connected to the 2x4 header.
+be connected to the 2x3 header.
+
+The Mother's vision is that if and when we do need to exercise an actual Li-ion
+battery with an actual Iota-controlled charging circuit, we will need to build
+a separate battery+charger board that will connect to the power input and BCI
+control interfaces on the Venus board.  That battery+charger board will feature
+an 18650 battery holder and a +5V charging power source connection, the charging
+current path (aside from BCI controls) will be contained entirely in that add-on
+board, whereas the battery power interface between Venus and the add-on board
+will carry only the load or discharge current.
+
+The reasons for changing the BCI header pinout from iWOW DSK and FC Caramel2 to
+a different one for FC Venus are as follows:
+
+* FC Tango (iWOW TR-800) module that forms the core of FC Caramel2 does not
+  bring out Iota VBATS as a separate signal - instead it is connected to the
+  VBAT supply inside the module.  However, if the charging current measurement
+  resistor will reside on a separate battery+charger board, then it would be
+  most proper to connect both VBATS and VCCS to the two sides of this resistor,
+  providing more accurate charging current measurement and CI control loop
+  operation.  Thus VBATS needs to be added to the BCI header.
+
+* ADIN1 and ADIN2 won't be needed when using a common off-the-shelf 18650
+  battery for prototyping - see section 1.10.1 for background information.
 
 3.5. LCD module and backlight