FreeCalypso > hg > freecalypso-tools
changeset 903:a7ad6b39e01b
tchtools/fc-tch2fr.c: update big header comment for new reality
author | Mychaela Falconia <falcon@freecalypso.org> |
---|---|
date | Wed, 28 Dec 2022 08:34:19 +0000 |
parents | 8ddb16a37273 |
children | 5041bcb8140f |
files | tchtools/fc-tch2fr.c |
diffstat | 1 files changed, 18 insertions(+), 21 deletions(-) [+] |
line wrap: on
line diff
--- a/tchtools/fc-tch2fr.c Wed Dec 28 07:52:30 2022 +0000 +++ b/tchtools/fc-tch2fr.c Wed Dec 28 08:34:19 2022 +0000 @@ -1,27 +1,24 @@ /* - * Our experimental Calypso firmware enables us to capture the output of - * the GSM 05.03 channel decoder in the DSP, i.e., the bits leaving the - * channel decoder and going into the speech decoder. Our fc-shell utility - * allows saving this capture to a file; the captured booty includes not only - * the expected 260 bits per frame, but also some DSP status words which are - * not fully understood, but which are believed to contain indications as to - * whether the decoded speech frame is good or bad. + * This program reads TCH downlink capture files in the old format from 2016 + * (the format which fc-shell tch record will write if the firmware running + * on the Calypso GSM device is an old version that emits TCH DL bits in + * the old format from 2016), completely *disregards* all 3 status words + * including the essential word of control flags, converts the 260-bit + * payload portion of each frame into standard libgsm/RTP format, and + * writes the result into a .gsm binary file. * - * My first naive thought was to save the captured speech frames in libgsm - * format so I could then play them with the 'play' command (SoX package) - * under Linux, but the problem with this naive approach is that the bad frames - * indication is lost, and some of the saved "speech" frames will contain - * utter garbage, resulting in very unkind-on-ears noises if that file is - * then played. I don't know what the proper solution should be; I don't know - * what the commercial cellphone implementations of the GSM 06.10 speech decoder - * (buried in black box DSPs) do when they get bad frames from the channel - * decoder. + * This program was written in 2016, at that time we (FreeCalypso team) + * did not have a proper understanding of how the complete TCH DL processing + * chain works - we particularly missed the Rx DTX handler block that MUST + * be present between the output of the GSM 05.03 channel decoder and the + * input to the GSM 06.10 speech decoder - and therefore the function + * performed by this program is a bogo-transform. * - * The present utility reproduces the naive behaviour of my previous - * implementation of fc-shell's tch record command: it takes hex files written - * by the current implementation of tch record in fc-shell, DISREGARDS the - * DSP status words, and blindly converts each 260-bit frame (good or bad) - * into libgsm format. + * This bogo-transform program is kept as part of FC host tools package + * only for backward compatibility - for actual decoding of TCH DL captures, + * please use our new gsmfr-dlcap-* and gsmefr-dlcap-* utilities that are + * maintained as part of Themyscira Wireless GSM codec libraries & utilities + * package. */ #include <sys/types.h>