OsmocomBB

This was originally a checklist item in #3400#note-15:

The non-adaptive codecs (HR, FR, EFR) are all confirmed to work. AMR implementation is
currently incomplete in trxcon, and is completely missing in the layer1 firmware (needs DSP patches).

Initial AMR support was recently added to trxcon by pespin:

commit a53e93fe9c81136b512697e169c5cf5ecd319163
Author: Pau Espin Pedrol <pespin@sysmocom.de>
Date:   Fri Sep 2 17:02:17 2022 +0200

    trxcon: Initial support for forwarding AMR

    This allows TTCN3 L1CTL module (used in BTS_Tests) to transmit and
    receive AMR payloads towards osmo-bts-trx.

    Related: SYS#5987
    Change-Id: Ia20bc96e39726a919a556c83c8be48cb31af7331

We need to investigate what needs to be done in order to support AMR calls, at least for trxcon.

One missing part is forwarding the AMR parameters to the L1 via L1CTL:

diff --git a/src/host/layer23/src/common/l1ctl.c b/src/host/layer23/src/common/l1ctl.c
index e33074af..d5204034 100644
--- a/src/host/layer23/src/common/l1ctl.c
+++ b/src/host/layer23/src/common/l1ctl.c
@@ -472,6 +472,7 @@ int l1ctl_tx_tch_mode_req(struct osmocom_ms *ms, uint8_t tch_mode,
        req->tch_mode = tch_mode;
        req->audio_mode = audio_mode;
        req->tch_loop_mode = tch_loop_mode;
+       /* TODO: Set AMR codec in req if req->tch_mode==GSM48_CMODE_SPEECH_AMR */

        return osmo_send_l1(ms, msg);
 }