OsmocomBB

This is the Analog Baseband Chip TWL3025

It consists of various functions, including

 * ADC and DAC for the GSM baseband signals

 * ADC and DAC for the Voice/Audio path

 * DAC for APC (Automatic Power Control)

 * DAC for AFC (Automatic Frequency Control)

 * Battery Charging Controller

 * LDO's (Linear Power Regulators)

The functions of the ABB are controlled by a register set.  The register set

is available through both USP and BSP.

== External Interfaces ==

=== USP (uController Serial Port) ===

This is the SPI-like control interface between DBB and the TWL3025 (ABB).

[[Image(Iota:twl3025_usp.png)]]

=== TSP (Timee Serial Port) ===

It is connected to the TSP controller inside the [wiki:Calypso] DBB.

The CLK6.5 Signal makes things a bit more complicated than we would like. The sequence of events is something like:

 * CLK_13M is applied continuously to TWL3025

 * nTEN is in default state of high (inactive)

 * internal CLK6.5 is in default state low

 * nTEN is asserted low by TPU, some 0..65ns before CLK_13M rising edge

 * next CLK13M falling edge starts first CLK6.5 rising edge

 * every falling edge of CLK13M toggles CLK6.5

 * TDR is sampled at every rising edge of CLK6.5 (including the first edge above)

 * 7 bits are transferred during seven rising edges of CLK6.5

 * TEN stays asserted for 1 CLK13M period after last bit is transferred

 * TEN needs to be released before next CLK13M rising edge to prevent another transfer

=== BSP (Baseband Serial Port) ===

This synchronous serial port is connected to the RIF (Radio InterFace) of the Calypso DBB.