[S] Change in libosmocore[master]: coding: clarify the USF decoding for PDCH blocks

fixeria has submitted this change. ( https://gerrit.osmocom.org/c/libosmocore/+/35257?usp=email ) Change subject: coding: clarify the USF decoding for PDCH blocks ...................................................................... coding: clarify the USF decoding for PDCH blocks The USF (Uplink State Flag) field is present in the MAC header of all Downlink PDCH blocks. It is used by the network to indicate which MS can transmit on subsequent Uplink PDCH block(s). This field is of a high importance for the MS, thus the decoder API allows the caller to obtain USF value separately from the actual data bits. In the case of gsm0503_pdtch_decode(), if the 'usf_p' pointer is not NULL, the USF value would be assigned for CS2/CS3/CS4 (but not CS1) even if the CRC check fails (negative return value). A subsequent patch is to bring the CS1 in consistency with CS2/CS3/CS4. In the case of gsm0503_pdtch_egprs_decode(), decoding of the USF field separately from data bits is not implemented, and moreover the function itself cannot be used for decoding Downlink blocks. Change-Id: I43e8bfb4003f34766ace7c5c6080ca583ce5efbb --- M src/coding/gsm0503_coding.c 1 file changed, 29 insertions(+), 2 deletions(-) Approvals: pespin: Looks good to me, approved laforge: Looks good to me, but someone else must approve Jenkins Builder: Verified diff --git a/src/coding/gsm0503_coding.c b/src/coding/gsm0503_coding.c index 612e0ad..5b78502 100644 --- a/src/coding/gsm0503_coding.c +++ b/src/coding/gsm0503_coding.c @@ -921,7 +921,7 @@ * \param[out] l2_data caller-allocated buffer for L2 Frame * \param[in] bursts burst input data as soft unpacked bits * \param[in] nbits number of bits in \a bursts - * \param usf_p unused argument ?!? + * \param usf_p Uplink State Flag, FIXME: not implemented * \param[out] n_errors number of detected bit-errors * \param[out] n_bits_total total number of decoded bits * \returns number of bytes decoded; negative on error */ @@ -1010,7 +1010,7 @@ /*! Decode GPRS PDTCH * \param[out] l2_data caller-allocated buffer for L2 Frame * \param[in] bursts burst input data as soft unpacked bits - * \param[out] usf_p uplink stealing flag + * \param[out] usf_p Uplink State Flag, only relevant for DL blocks * \param[out] n_errors number of detected bit-errors * \param[out] n_bits_total total number of dcoded bits * \returns number of bytes decoded; negative on error */ @@ -1061,6 +1061,7 @@ osmo_conv_decode_ber(&gsm0503_cs2_np, cB, conv, n_errors, n_bits_total); + /* 5.1.2.2 a) the three USF bits d(0),d(1),d(2) are precoded into six bits */ for (i = 0; i < 8; i++) { for (j = 0, k = 0; j < 6; j++) k += abs(((int)gsm0503_usf2six[i][j]) - ((int)conv[j])); @@ -1096,6 +1097,7 @@ osmo_conv_decode_ber(&gsm0503_cs3_np, cB, conv, n_errors, n_bits_total); + /* 5.1.3.2 a) the three USF bits d(0),d(1),d(2) are precoded into six bits */ for (i = 0; i < 8; i++) { for (j = 0, k = 0; j < 6; j++) k += abs(((int)gsm0503_usf2six[i][j]) - ((int)conv[j])); @@ -1124,6 +1126,7 @@ for (i = 12; i < 456; i++) conv[i] = (cB[i] < 0) ? 1 : 0; + /* 5.1.4.2 a) the three USF bits d(0),d(1),d(2) are precoded into twelve bits */ for (i = 0; i < 8; i++) { for (j = 0, k = 0; j < 12; j++) k += abs(((int)gsm0503_usf2twelve_sbit[i][j]) - ((int)cB[j])); -- To view, visit https://gerrit.osmocom.org/c/libosmocore/+/35257?usp=email To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: libosmocore Gerrit-Branch: master Gerrit-Change-Id: I43e8bfb4003f34766ace7c5c6080ca583ce5efbb Gerrit-Change-Number: 35257 Gerrit-PatchSet: 1 Gerrit-Owner: fixeria &lt;vyanitskiy(a)sysmocom.de&gt; Gerrit-Reviewer: Jenkins Builder Gerrit-Reviewer: fixeria &lt;vyanitskiy(a)sysmocom.de&gt; Gerrit-Reviewer: laforge &lt;laforge(a)osmocom.org&gt; Gerrit-Reviewer: pespin &lt;pespin(a)sysmocom.de&gt; Gerrit-MessageType: merged