mirror of https://gerrit.osmocom.org/libosmocore
coding: fix bit ordering in 11-bit RACH coding functions
According to 3GPP TS 44.004, figure 7.4a.b, the format of 11-bit RACH uplink / Uplink access burst block is as defined follows: <--------------------------------------------------- 8 7 6 5 4 3 2 1 +--------------------------------------------------+ | 11 bit RACH uplink / Uplink access burst block | OCT1 +--------------------------------------------------+ | | OCT2 +-------------------+ As was (correctly) assumed in [1], the bit ordering in 11-bit RACH coding functions is wrong. The problem is that neither of generic functions from bit16gen.h can be used to load / store the RA11 value (regardless of the endianness), because they assume that the payload is 16 bit long. With this patch applied, RA11 values from [1] look correct: < EGPRS Packet channel request message content > ::= < Signalling : 110011 < RandomBits : 00111 > > | < Signalling : 110011 < RandomBits : 00110 > > | < Signalling : 110011 < RandomBits : 01111 > > | < Signalling : 110011 < RandomBits : 01100 > > | < Signalling : 110011 < RandomBits : 00111 > > | < Signalling : 110011 < RandomBits : 10110 > > ; [1] Id80e471d252b9416217b56f4c8c0a8f5f1289fee Change-Id: I43d30611dd69f77f2b3b46f4b56056a8891d3c24 Related: OS#1548
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@ -2879,7 +2879,7 @@ static inline int16_t rach_decode_ber(const sbit_t *burst, uint8_t bsic, bool is
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osmo_ubit2pbit_ext(ra, 0, conv, 0, nbits, 1);
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return is_11bit ? osmo_load16le(ra) : ra[0];
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return is_11bit ? ((ra[0] << 3) | (ra[1] & 0x07)) : ra[0];
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}
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/*! Decode the Extended (11-bit) RACH according to 3GPP TS 45.003
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@ -2974,7 +2974,8 @@ int gsm0503_rach_ext_encode(ubit_t *burst, uint16_t ra11, uint8_t bsic, bool is_
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uint8_t ra[2] = { 0 }, nbits = 8;
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if (is_11bit) {
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osmo_store16le(ra11, ra);
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ra[0] = (uint8_t) (ra11 >> 3);
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ra[1] = (uint8_t) (ra11 & 0x07);
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nbits = 11;
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} else
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ra[0] = (uint8_t)ra11;
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@ -40,12 +40,12 @@ S-Bits:
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Decoded: 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17
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xcch_decode: n_errors=60 n_bits_total=456 ber=0.13
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Decoded RA11: 0x7cc
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Decoded RA11: 0x6cc
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Decoded RA11: 0x7cd
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Decoded RA11: 0x4cd
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Decoded RA11: 0x7cc
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Decoded RA11: 0x6ce
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Decoded RA11: 0x667
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Decoded RA11: 0x666
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Decoded RA11: 0x66f
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Decoded RA11: 0x66c
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Decoded RA11: 0x667
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Decoded RA11: 0x676
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Encoding: 03 03 01 00
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U-Bits: 111001110011000011100111001100001101001111000000000011010000011010110111111100
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