diff options
Diffstat (limited to 'src/gsm/rlp.c')
| -rw-r--r-- | src/gsm/rlp.c | 243 |
1 files changed, 243 insertions, 0 deletions
diff --git a/src/gsm/rlp.c b/src/gsm/rlp.c new file mode 100644 index 00000000..1e90a689 --- /dev/null +++ b/src/gsm/rlp.c @@ -0,0 +1,243 @@ +/* + * Copyright (C) 2022-2023 Harald Welte <laforge@osmocom.org> + * + * All Rights Reserved + * + * SPDX-License-Identifier: GPL-2.0+ + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + */ + +/*! \addtogroup rlp + * @{ + * RLP (Radio Link Protocol) as per 3GPP TS 24.022 + * + */ + +#include <stdint.h> +#include <stddef.h> +#include <string.h> +#include <errno.h> + +#include <osmocom/gsm/rlp.h> + +const struct value_string osmo_rlp_ftype_vals[] = { + { OSMO_RLP_FT_U, "U" }, + { OSMO_RLP_FT_S, "S" }, + { OSMO_RLP_FT_IS, "IS" }, + { 0, NULL } +}; + +const struct value_string osmo_rlp_ftype_u_vals[] = { + { OSMO_RLP_U_FT_SABM, "SABM" }, + { OSMO_RLP_U_FT_UA, "UA" }, + { OSMO_RLP_U_FT_DISC, "DISC" }, + { OSMO_RLP_U_FT_DM, "DM" }, + { OSMO_RLP_U_FT_NULL, "NULL" }, + { OSMO_RLP_U_FT_UI, "UI" }, + { OSMO_RLP_U_FT_XID, "XID" }, + { OSMO_RLP_U_FT_TEST, "TEST" }, + { OSMO_RLP_U_FT_REMAP, "REMAP" }, + { 0, NULL } +}; + +const struct value_string osmo_rlp_ftype_s_vals[] = { + { OSMO_RLP_S_FT_RR, "RR" }, + { OSMO_RLP_S_FT_REJ, "REJ" }, + { OSMO_RLP_S_FT_RNR, "RNR" }, + { OSMO_RLP_S_FT_SREJ, "SREJ" }, + { 0, NULL } +}; + +/* number of bytes used up by FCS */ +#define FCS_SIZE_BYTES 3 + +/*! decode a RLP frame into its abstract representation. Doesn't check FCS correctness. + * \param[out] out caller-allocated memory for output of decoded frame + * \param[in] version RLP version number to use when decoding + * \param[in] data raw RLP frame input data + * \param[in] data_len length of data (in octets); must be 30 (240bit) or 72 (576bit) + * \returns 0 in case of success; negative on error */ +int osmo_rlp_decode(struct osmo_rlp_frame_decoded *out, uint8_t version, const uint8_t *data, size_t data_len) +{ + const uint8_t hdr_len = 2; /* will become a variable when we introduce v2 support */ + uint8_t n_s, n_r; + + if (data_len != 240/8 && data_len != 576/8) + return -EINVAL; + + /* we only support version 0+1 so far */ + if (version >= 2) + return -ENOTSUP; + + memset(out, 0, sizeof(*out)); + out->version = version; + + out->c_r = data[0] & 1; + n_s = (data[0] >> 3) | (data[1] & 1) << 5; + n_r = (data[1] >> 2); + out->fcs = (data[data_len-1] << 16) | (data[data_len-2]) << 8 | (data[data_len-3] << 0); + out->p_f = (data[1] >> 1) & 1; + + switch (n_s) { + case 0x3f: + out->ftype = OSMO_RLP_FT_U; + out->u_ftype = n_r & 0x1f; + if (out->u_ftype == OSMO_RLP_U_FT_XID) { + memcpy(out->info, data + hdr_len, data_len - (hdr_len + FCS_SIZE_BYTES)); + out->info_len = data_len - (hdr_len + FCS_SIZE_BYTES); + } + break; + case 0x3e: + out->ftype = OSMO_RLP_FT_S; + out->s_ftype = (data[0] >> 1) & 3; + out->n_r = n_r; + break; + default: + out->ftype = OSMO_RLP_FT_IS; + out->s_ftype = (data[0] >> 1) & 3; + out->n_s = n_s; + out->n_r = n_r; + memcpy(out->info, data + hdr_len, data_len - (hdr_len + FCS_SIZE_BYTES)); + out->info_len = data_len - (2 + 3); + break; + } + + return 0; +} + +/*! encode a RLP frame from its abstract representation. Generates FCS. + * \param[out] out caller-allocated output buffer + * \param[in] out_size size of output buffer (in octets); must be 30 (240bit) or 72 (576bit) + * \param[in] in decoded RLP frame which is to be encoded + * \returns number of output bytes used; negative on error */ +int osmo_rlp_encode(uint8_t *out, size_t out_size, const struct osmo_rlp_frame_decoded *in) +{ + const uint8_t hdr_len = 2; /* will become a variable when we introduce v2 support */ + uint8_t n_s, n_r, s_bits; + uint32_t fcs; + + /* we only support version 0+1 so far */ + if (in->version >= 2) + return -ENOTSUP; + + if (out_size != 240/8 && out_size != 576/8) + return -EINVAL; + + memset(out, 0, out_size); + + if (in->c_r) + out[0] |= 0x01; + if (in->p_f) + out[1] |= 0x02; + + switch (in->ftype) { + case OSMO_RLP_FT_U: + n_s = 0x3f; + n_r = in->u_ftype; + s_bits = 0; + if (in->u_ftype == OSMO_RLP_U_FT_XID) { + if (in->info_len > out_size - (hdr_len + FCS_SIZE_BYTES)) + return -EINVAL; + memcpy(out+hdr_len, in->info, in->info_len); + } + break; + case OSMO_RLP_FT_S: + n_s = 0x3e; + n_r = in->n_r; + s_bits = in->s_ftype; + break; + case OSMO_RLP_FT_IS: + /* we only support 240 bit so far */ + if (in->info_len > out_size - (hdr_len + FCS_SIZE_BYTES)) + return -EINVAL; + n_s = in->n_s; + n_r = in->n_r; + s_bits = in->s_ftype; + memcpy(out+hdr_len, in->info, in->info_len); + break; + default: + return -EINVAL; + } + + /* patch N(S) into output data */ + out[0] |= (n_s & 0x1F) << 3; + out[1] |= (n_s & 0x20) >> 5; + + /* patch N(R) / M-bits into output data */ + out[1] |= (n_r & 0x3f) << 2; + + /* patch S-bits into output data */ + out[0] |= (s_bits & 3) << 1; + + /* compute FCS + add it to end of frame */ + fcs = osmo_rlp_fcs_compute(out, out_size - FCS_SIZE_BYTES); + out[out_size - 3] = (fcs >> 0) & 0xff; + out[out_size - 2] = (fcs >> 8) & 0xff; + out[out_size - 1] = (fcs >> 16) & 0xff; + + return out_size; +} + + +static const uint32_t rlp_fcs_table[256] = { + 0x00B29D2D, 0x00643A5B, 0x0044D87A, 0x00927F0C, 0x00051C38, 0x00D3BB4E, 0x00F3596F, 0x0025FE19, + 0x008694BC, 0x005033CA, 0x0070D1EB, 0x00A6769D, 0x003115A9, 0x00E7B2DF, 0x00C750FE, 0x0011F788, + 0x00DA8E0F, 0x000C2979, 0x002CCB58, 0x00FA6C2E, 0x006D0F1A, 0x00BBA86C, 0x009B4A4D, 0x004DED3B, + 0x00EE879E, 0x003820E8, 0x0018C2C9, 0x00CE65BF, 0x0059068B, 0x008FA1FD, 0x00AF43DC, 0x0079E4AA, + 0x0062BB69, 0x00B41C1F, 0x0094FE3E, 0x00425948, 0x00D53A7C, 0x00039D0A, 0x00237F2B, 0x00F5D85D, + 0x0056B2F8, 0x0080158E, 0x00A0F7AF, 0x007650D9, 0x00E133ED, 0x0037949B, 0x001776BA, 0x00C1D1CC, + 0x000AA84B, 0x00DC0F3D, 0x00FCED1C, 0x002A4A6A, 0x00BD295E, 0x006B8E28, 0x004B6C09, 0x009DCB7F, + 0x003EA1DA, 0x00E806AC, 0x00C8E48D, 0x001E43FB, 0x008920CF, 0x005F87B9, 0x007F6598, 0x00A9C2EE, + 0x0049DA1E, 0x009F7D68, 0x00BF9F49, 0x0069383F, 0x00FE5B0B, 0x0028FC7D, 0x00081E5C, 0x00DEB92A, + 0x007DD38F, 0x00AB74F9, 0x008B96D8, 0x005D31AE, 0x00CA529A, 0x001CF5EC, 0x003C17CD, 0x00EAB0BB, + 0x0021C93C, 0x00F76E4A, 0x00D78C6B, 0x00012B1D, 0x00964829, 0x0040EF5F, 0x00600D7E, 0x00B6AA08, + 0x0015C0AD, 0x00C367DB, 0x00E385FA, 0x0035228C, 0x00A241B8, 0x0074E6CE, 0x005404EF, 0x0082A399, + 0x0099FC5A, 0x004F5B2C, 0x006FB90D, 0x00B91E7B, 0x002E7D4F, 0x00F8DA39, 0x00D83818, 0x000E9F6E, + 0x00ADF5CB, 0x007B52BD, 0x005BB09C, 0x008D17EA, 0x001A74DE, 0x00CCD3A8, 0x00EC3189, 0x003A96FF, + 0x00F1EF78, 0x0027480E, 0x0007AA2F, 0x00D10D59, 0x00466E6D, 0x0090C91B, 0x00B02B3A, 0x00668C4C, + 0x00C5E6E9, 0x0013419F, 0x0033A3BE, 0x00E504C8, 0x007267FC, 0x00A4C08A, 0x008422AB, 0x005285DD, + 0x001F18F0, 0x00C9BF86, 0x00E95DA7, 0x003FFAD1, 0x00A899E5, 0x007E3E93, 0x005EDCB2, 0x00887BC4, + 0x002B1161, 0x00FDB617, 0x00DD5436, 0x000BF340, 0x009C9074, 0x004A3702, 0x006AD523, 0x00BC7255, + 0x00770BD2, 0x00A1ACA4, 0x00814E85, 0x0057E9F3, 0x00C08AC7, 0x00162DB1, 0x0036CF90, 0x00E068E6, + 0x00430243, 0x0095A535, 0x00B54714, 0x0063E062, 0x00F48356, 0x00222420, 0x0002C601, 0x00D46177, + 0x00CF3EB4, 0x001999C2, 0x00397BE3, 0x00EFDC95, 0x0078BFA1, 0x00AE18D7, 0x008EFAF6, 0x00585D80, + 0x00FB3725, 0x002D9053, 0x000D7272, 0x00DBD504, 0x004CB630, 0x009A1146, 0x00BAF367, 0x006C5411, + 0x00A72D96, 0x00718AE0, 0x005168C1, 0x0087CFB7, 0x0010AC83, 0x00C60BF5, 0x00E6E9D4, 0x00304EA2, + 0x00932407, 0x00458371, 0x00656150, 0x00B3C626, 0x0024A512, 0x00F20264, 0x00D2E045, 0x00044733, + 0x00E45FC3, 0x0032F8B5, 0x00121A94, 0x00C4BDE2, 0x0053DED6, 0x008579A0, 0x00A59B81, 0x00733CF7, + 0x00D05652, 0x0006F124, 0x00261305, 0x00F0B473, 0x0067D747, 0x00B17031, 0x00919210, 0x00473566, + 0x008C4CE1, 0x005AEB97, 0x007A09B6, 0x00ACAEC0, 0x003BCDF4, 0x00ED6A82, 0x00CD88A3, 0x001B2FD5, + 0x00B84570, 0x006EE206, 0x004E0027, 0x0098A751, 0x000FC465, 0x00D96313, 0x00F98132, 0x002F2644, + 0x00347987, 0x00E2DEF1, 0x00C23CD0, 0x00149BA6, 0x0083F892, 0x00555FE4, 0x0075BDC5, 0x00A31AB3, + 0x00007016, 0x00D6D760, 0x00F63541, 0x00209237, 0x00B7F103, 0x00615675, 0x0041B454, 0x00971322, + 0x005C6AA5, 0x008ACDD3, 0x00AA2FF2, 0x007C8884, 0x00EBEBB0, 0x003D4CC6, 0x001DAEE7, 0x00CB0991, + 0x00686334, 0x00BEC442, 0x009E2663, 0x00488115, 0x00DFE221, 0x00094557, 0x0029A776, 0x00FF0000 +}; + +/*! compute RLP FCS according to 3GPP TS 24.022 Section 4.4. + * \param[in] in input data over which to compute FCS + * \param[in] in_len length of input data (in octets) + * \returns computed frame check sequence (FCS). */ +uint32_t osmo_rlp_fcs_compute(const uint8_t *in, size_t in_len) +{ + uint32_t divider = 0; + size_t i; + + for (i = 0; i < in_len; i++) { + uint8_t input = in[i] ^ (divider & 0xff); + divider = (divider >> 8) ^ rlp_fcs_table[input]; + } + + return divider; +} + +/*! @} */ |