edge: Add unified decoder methods for GPRS/EGPRS
This commit adds new RLC block decoder functions that support both
GPRS and EGPRS. The code path is selected based on the value of the
GprsCodingScheme cs object.
- rlc_parse_ul_data_header
parses the header of an RLC data block including the E and FBI/TI
flags (currently supported CS-1 - CS-4, MCS-1 - MCS-4).
- rlc_copy_to_aligned_buffer
copies an RLC data unit to a byte aligned buffer and returns
the unit's length.
- rlc_get_data_aligned
is a convenience wrapper around rlc_copy_to_aligned_buffer
that avoids copying if the data unit is already byte aligned.
Sponsored-by: On-Waves ehf
diff --git a/src/decoding.cpp b/src/decoding.cpp
index d4f014b..a26377b 100644
--- a/src/decoding.cpp
+++ b/src/decoding.cpp
@@ -21,11 +21,267 @@
#include <rlc.h>
#include <gprs_debug.h>
+extern "C" {
+#include <osmocom/core/utils.h>
+}
+
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>
+#define LENGTH_TO_END 255
+/*
+ * \returns num extensions fields (num frames == offset) on success,
+ * -errno otherwise.
+ */
+static int parse_extensions_egprs(const uint8_t *data, unsigned int data_len,
+ unsigned int *offs,
+ bool is_last_block,
+ Decoding::RlcData *chunks, unsigned int chunks_size)
+{
+ const struct rlc_li_field_egprs *li;
+ uint8_t e;
+ unsigned int num_chunks = 0;
+ // unsigned int data_area = 0;
+
+ e = 0;
+ while (!e) {
+ if (*offs > data_len) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA LI extended, "
+ "but no more data\n");
+ return -EINVAL;
+ }
+
+ /* get new E */
+ li = (struct rlc_li_field_egprs *)&data[*offs];
+ e = li->e;
+ *offs += 1;
+
+ if (!chunks)
+ continue;
+
+ if (num_chunks == chunks_size) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA LI extended, "
+ "but no more chunks possible\n");
+ return -ENOSPC;
+ }
+ if (li->li == 0 && num_chunks == 0 && li->e == 0) {
+ /* TS 44.060, table 10.4.14a.1, row 2a */
+ chunks[num_chunks].length = 0;
+ chunks[num_chunks].is_complete = true;
+ } else if (li->li == 0 && num_chunks == 0 && li->e == 1) {
+ /* TS 44.060, table 10.4.14a.1, row 4 */
+ // chunks[num_chunks].length = data_len - *offs - data_area;
+ chunks[num_chunks].length = LENGTH_TO_END;
+ chunks[num_chunks].is_complete = is_last_block;
+ } else if (li->li == 127 && li->e == 1) {
+ /* TS 44.060, table 10.4.14a.1, row 3 & 5 */
+ /* only filling bytes left */
+ break;
+ } else if (li->li > 0) {
+ /* TS 44.060, table 10.4.14a.1, row 1 & 2b */
+ chunks[num_chunks].length = li->li;
+ chunks[num_chunks].is_complete = true;
+ } else {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA LI contains "
+ "invalid extension octet: LI=%d, E=%d, count=%d\n",
+ li->li, li->e, num_chunks);
+ return -EINVAL;
+ }
+
+ num_chunks += 1;
+
+ if (e == 1) {
+ /* There is space after the last chunk, add a final one */
+ if (num_chunks == chunks_size) {
+ LOGP(DRLCMACUL, LOGL_NOTICE,
+ "UL DATA LI possibly extended, "
+ "but no more chunks possible\n");
+ return -ENOSPC;
+ }
+
+ // chunks[num_chunks].length = data_len - *offs - data_area;
+ chunks[num_chunks].length = LENGTH_TO_END;
+ chunks[num_chunks].is_complete = is_last_block;
+ // data_area += chunks[num_chunks].length;
+ num_chunks += 1;
+ }
+ }
+
+ return num_chunks;
+}
+
+static int parse_extensions_gprs(const uint8_t *data, unsigned int data_len,
+ unsigned int *offs,
+ bool is_last_block,
+ Decoding::RlcData *chunks, unsigned int chunks_size)
+{
+ const struct rlc_li_field *li;
+ uint8_t m, e;
+ unsigned int num_chunks = 0;
+ // unsigned int data_area = 0;
+
+ e = 0;
+ while (!e) {
+ if (*offs > data_len) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA LI extended, "
+ "but no more data\n");
+ return -EINVAL;
+ }
+
+ /* get new E */
+ li = (const struct rlc_li_field *)&data[*offs];
+ e = li->e;
+ m = li->m;
+ *offs += 1;
+
+ if (li->li == 0) {
+ /* TS 44.060, 10.4.14, par 6 */
+ e = 1;
+ m = 0;
+ }
+
+ /* TS 44.060, table 10.4.13.1 */
+ if (m == 0 && e == 0) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA "
+ "ignored, because M='0' and E='0'.\n");
+ return 0;
+ }
+
+ if (!chunks)
+ continue;
+
+ if (num_chunks == chunks_size) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA LI extended, "
+ "but no more chunks possible\n");
+ return -ENOSPC;
+ }
+
+ if (li->li == 0)
+ /* e is 1 here */
+ // chunks[num_chunks].length = data_len - *offs - data_area;
+ chunks[num_chunks].length = LENGTH_TO_END;
+ else
+ chunks[num_chunks].length = li->li;
+
+ chunks[num_chunks].is_complete = li->li || is_last_block;
+
+ // data_area += chunks[num_chunks].length;
+ num_chunks += 1;
+
+ if (e == 1 && m == 1) {
+ if (num_chunks == chunks_size) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA LI extended, "
+ "but no more chunks possible\n");
+ return -ENOSPC;
+ }
+ /* TS 44.060, 10.4.13.1, row 4 */
+ // chunks[num_chunks].length = data_len - *offs - data_area;
+ chunks[num_chunks].length = LENGTH_TO_END;
+ chunks[num_chunks].is_complete = is_last_block;
+ num_chunks += 1;
+ }
+ }
+
+ return num_chunks;
+}
+
+int Decoding::rlc_data_from_ul_data(
+ const struct gprs_rlc_ul_data_block_info *rdbi, GprsCodingScheme cs,
+ const uint8_t *data, RlcData *chunks, unsigned int chunks_size,
+ uint32_t *tlli)
+{
+ uint8_t e;
+ unsigned int data_len = rdbi->data_len;
+ unsigned int num_chunks = 0, i;
+ unsigned int offs = 0;
+ bool is_last_block = (rdbi->cv == 0);
+
+ if (!chunks)
+ chunks_size = 0;
+
+ e = rdbi->e;
+ if (e) {
+ if (chunks_size > 0) {
+ chunks[num_chunks].offset = offs;
+ chunks[num_chunks].length = LENGTH_TO_END;
+ chunks[num_chunks].is_complete = is_last_block;
+ num_chunks += 1;
+ } else if (chunks) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "No extension, "
+ "but no more chunks possible\n");
+ return -ENOSPC;
+ }
+ } else if (cs.isEgprs()) {
+ /* if E is not set (LI follows), EGPRS */
+ num_chunks = parse_extensions_egprs(data, data_len, &offs,
+ is_last_block,
+ chunks, chunks_size);
+ } else {
+ /* if E is not set (LI follows), GPRS */
+ num_chunks = parse_extensions_gprs(data, data_len, &offs,
+ is_last_block,
+ chunks, chunks_size);
+ }
+
+ /* TLLI */
+ if (rdbi->ti) {
+ uint32_t tlli_enc;
+ if (offs + 4 > data_len) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA TLLI out of block "
+ "border\n");
+ return -EINVAL;
+ }
+
+ memcpy(&tlli_enc, data + offs, sizeof(tlli_enc));
+ if (cs.isGprs())
+ /* The TLLI is encoded in big endian for GPRS (see
+ * TS 44.060, figure 10.2.2.1, note) */
+ *tlli = be32toh(tlli_enc);
+ else
+ /* The TLLI is encoded in little endian for EGPRS (see
+ * TS 44.060, figure 10.3a.2.1, note 2) */
+ *tlli = le32toh(tlli_enc);
+
+ offs += sizeof(tlli_enc);
+ } else {
+ *tlli = 0;
+ }
+
+ /* PFI */
+ if (rdbi->pi) {
+ LOGP(DRLCMACUL, LOGL_ERROR, "ERROR: PFI not supported, "
+ "please disable in SYSTEM INFORMATION\n");
+ return -ENOTSUP;
+
+ /* TODO: Skip all extensions with E=0 (see TS 44.060, 10.4.11 */
+ }
+
+ /* LLC */
+ for (i = 0; i < num_chunks; i++) {
+ chunks[i].offset = offs;
+ if (chunks[i].length == LENGTH_TO_END) {
+ if (offs == data_len) {
+ /* There is no place for an additional chunk,
+ * so drop it (this may happen with EGPRS since
+ * there is no M flag. */
+ num_chunks -= 1;
+ break;;
+ }
+ chunks[i].length = data_len - offs;
+ }
+ offs += chunks[i].length;
+ if (offs > data_len) {
+ LOGP(DRLCMACUL, LOGL_NOTICE, "UL DATA out of block "
+ "border, chunk idx: %d, size: %d\n",
+ i, chunks[i].length);
+ return -EINVAL;
+ }
+ }
+
+ return num_chunks;
+}
int Decoding::tlli_from_ul_data(const uint8_t *data, uint8_t len,
uint32_t *tlli)
@@ -114,3 +370,169 @@
show_rbb[64] = '\0';
}
+
+int Decoding::rlc_parse_ul_data_header(struct gprs_rlc_ul_header_egprs *rlc,
+ const uint8_t *data, GprsCodingScheme cs)
+{
+ const struct gprs_rlc_ul_header_egprs_3 *egprs3;
+ const struct rlc_ul_header *gprs;
+ unsigned int e_ti_header;
+ unsigned int cur_bit = 0;
+ unsigned int data_len = 0;
+
+ rlc->cs = cs;
+
+ data_len = cs.maxDataBlockBytes();
+
+ switch(cs.headerTypeData()) {
+ case GprsCodingScheme::HEADER_GPRS_DATA:
+ gprs = static_cast<struct rlc_ul_header *>
+ ((void *)data);
+ rlc->r = gprs->r;
+ rlc->si = gprs->si;
+ rlc->tfi = gprs->tfi;
+ rlc->cps = 0;
+ rlc->rsb = 0;
+
+ rlc->num_data_blocks = 1;
+ rlc->block_info[0].cv = gprs->cv;
+ rlc->block_info[0].pi = gprs->pi;
+ rlc->block_info[0].bsn = gprs->bsn;
+ rlc->block_info[0].e = gprs->e;
+ rlc->block_info[0].ti = gprs->ti;
+ rlc->block_info[0].spb = 0;
+
+ cur_bit += 3 * 8;
+
+ rlc->data_offs_bits[0] = cur_bit;
+ rlc->block_info[0].data_len = data_len;
+ cur_bit += data_len * 8;
+
+ break;
+ case GprsCodingScheme::HEADER_EGPRS_DATA_TYPE_3:
+ egprs3 = static_cast<struct gprs_rlc_ul_header_egprs_3 *>
+ ((void *)data);
+ rlc->r = egprs3->r;
+ rlc->si = egprs3->si;
+ rlc->tfi = (egprs3->tfi_a << 0) | (egprs3->tfi_b << 2);
+ rlc->cps = (egprs3->cps_a << 0) | (egprs3->cps_b << 2);
+ rlc->rsb = egprs3->rsb;
+
+ rlc->num_data_blocks = 1;
+ rlc->block_info[0].cv = egprs3->cv;
+ rlc->block_info[0].pi = egprs3->pi;
+ rlc->block_info[0].spb = egprs3->spb;
+ rlc->block_info[0].bsn =
+ (egprs3->bsn1_a << 0) | (egprs3->bsn1_b << 5);
+
+ cur_bit += 3 * 8 + 7;
+
+ e_ti_header = (data[3] + (data[4] << 8)) >> 7;
+ rlc->block_info[0].e = !!(e_ti_header & 0x01);
+ rlc->block_info[0].ti = !!(e_ti_header & 0x02);
+ cur_bit += 2;
+
+ rlc->data_offs_bits[0] = cur_bit;
+ rlc->block_info[0].data_len = data_len;
+ cur_bit += data_len * 8;
+
+ break;
+
+ case GprsCodingScheme::HEADER_EGPRS_DATA_TYPE_1:
+ case GprsCodingScheme::HEADER_EGPRS_DATA_TYPE_2:
+ /* TODO: Support both header types */
+ /* fall through */
+ default:
+ LOGP(DRLCMACDL, LOGL_ERROR,
+ "Decoding of uplink %s data blocks not yet supported.\n",
+ cs.name());
+ return -ENOTSUP;
+ };
+
+ return cur_bit;
+}
+
+/**
+ * \brief Copy LSB bitstream RLC data block to byte aligned buffer.
+ *
+ * Note that the bitstream is encoded in LSB first order, so the two octets
+ * 654321xx xxxxxx87 contain the octet 87654321 starting at bit position 3
+ * (LSB has bit position 1). This is a different order than the one used by
+ * CSN.1.
+ *
+ * \param data_block_idx The block index, 0..1 for header type 1, 0 otherwise
+ * \param src A pointer to the start of the RLC block (incl. the header)
+ * \param buffer A data area of a least the size of the RLC block
+ * \returns the number of bytes copied
+ */
+unsigned int Decoding::rlc_copy_to_aligned_buffer(
+ const struct gprs_rlc_ul_header_egprs *rlc,
+ unsigned int data_block_idx,
+ const uint8_t *src, uint8_t *buffer)
+{
+ unsigned int hdr_bytes;
+ unsigned int extra_bits;
+ unsigned int i;
+
+ uint8_t c, last_c;
+ uint8_t *dst;
+ const struct gprs_rlc_ul_data_block_info *rdbi;
+
+ OSMO_ASSERT(data_block_idx < rlc->num_data_blocks);
+ rdbi = &rlc->block_info[data_block_idx];
+
+ hdr_bytes = rlc->data_offs_bits[data_block_idx] >> 3;
+ extra_bits = (rlc->data_offs_bits[data_block_idx] & 7);
+
+ if (extra_bits == 0) {
+ /* It is aligned already */
+ memmove(buffer, src + hdr_bytes, rdbi->data_len);
+ return rdbi->data_len;
+ }
+
+ dst = buffer;
+ src = src + hdr_bytes;
+ last_c = *(src++);
+
+ for (i = 0; i < rdbi->data_len; i++) {
+ c = src[i];
+ *(dst++) = (last_c >> extra_bits) | (c << (8 - extra_bits));
+ last_c = c;
+ }
+
+ return rdbi->data_len;
+}
+
+/**
+ * \brief Get a pointer to byte aligned RLC data.
+ *
+ * Since the RLC data may not be byte aligned to the RLC block data such that a
+ * single RLC data byte is spread over two RLC block bytes, this function
+ * eventually uses the provided buffer as data storage.
+ *
+ * \param src A pointer to the start of the RLC block (incl. the header)
+ * \param buffer A data area of a least the size of the RLC block
+ * \returns A pointer to the RLC data start within src if it is aligned, and
+ * buffer otherwise.
+ */
+const uint8_t *Decoding::rlc_get_data_aligned(
+ const struct gprs_rlc_ul_header_egprs *rlc,
+ unsigned int data_block_idx,
+ const uint8_t *src, uint8_t *buffer)
+{
+ unsigned int hdr_bytes;
+ unsigned int extra_bits;
+
+ OSMO_ASSERT(data_block_idx < ARRAY_SIZE(rlc->data_offs_bits));
+
+ hdr_bytes = rlc->data_offs_bits[data_block_idx] >> 3;
+ extra_bits = (rlc->data_offs_bits[data_block_idx] & 7);
+
+ if (extra_bits == 0)
+ /* It is aligned already, return a pointer that refers to the
+ * original data. */
+ return src + hdr_bytes;
+
+ Decoding::rlc_copy_to_aligned_buffer(rlc, data_block_idx, src, buffer);
+ return buffer;
+}
diff --git a/src/decoding.h b/src/decoding.h
index 03dad47..1cda7b4 100644
--- a/src/decoding.h
+++ b/src/decoding.h
@@ -20,15 +20,37 @@
#pragma once
#include <gsm_rlcmac.h>
+#include "rlc.h"
#include <stdint.h>
class Decoding {
public:
+ struct RlcData {
+ uint8_t offset;
+ uint8_t length;
+ bool is_complete;
+ };
+
static int tlli_from_ul_data(const uint8_t *data, uint8_t len,
uint32_t *tlli);
+ static int rlc_data_from_ul_data(
+ const struct gprs_rlc_ul_data_block_info *rdbi,
+ GprsCodingScheme cs, const uint8_t *data, RlcData *chunks,
+ unsigned int chunks_size, uint32_t *tlli);
static uint8_t get_ms_class_by_capability(MS_Radio_Access_capability_t *cap);
static uint8_t get_egprs_ms_class_by_capability(MS_Radio_Access_capability_t *cap);
static void extract_rbb(const uint8_t *rbb, char *extracted_rbb);
+
+ static int rlc_parse_ul_data_header(struct gprs_rlc_ul_header_egprs *rlc,
+ const uint8_t *data, GprsCodingScheme cs);
+ static unsigned int rlc_copy_to_aligned_buffer(
+ const struct gprs_rlc_ul_header_egprs *rlc,
+ unsigned int data_block_idx,
+ const uint8_t *src, uint8_t *buffer);
+ static const uint8_t *rlc_get_data_aligned(
+ const struct gprs_rlc_ul_header_egprs *rlc,
+ unsigned int data_block_idx,
+ const uint8_t *src, uint8_t *buffer);
};
diff --git a/src/rlc.cpp b/src/rlc.cpp
index 42b602c..9f5c61d 100644
--- a/src/rlc.cpp
+++ b/src/rlc.cpp
@@ -20,6 +20,8 @@
#include "bts.h"
#include "gprs_debug.h"
+#include <errno.h>
+
extern "C" {
#include <osmocom/core/utils.h>
}
diff --git a/src/rlc.h b/src/rlc.h
index 89af219..bafe6a8 100644
--- a/src/rlc.h
+++ b/src/rlc.h
@@ -19,6 +19,8 @@
*/
#pragma once
+#include "gprs_coding_scheme.h"
+
#include <osmocom/core/endian.h>
#include <stdint.h>
@@ -53,6 +55,28 @@
return (RLC_MAX_SNS / 2) - 1;
}
+struct gprs_rlc_ul_data_block_info {
+ unsigned int data_len; /* EGPRS: N2, GPRS: N2-2, N-2 */
+ unsigned int bsn;
+ unsigned int ti;
+ unsigned int e;
+ unsigned int cv;
+ unsigned int pi;
+ unsigned int spb;
+};
+
+struct gprs_rlc_ul_header_egprs {
+ GprsCodingScheme cs;
+ unsigned int r;
+ unsigned int si;
+ unsigned int tfi;
+ unsigned int cps;
+ unsigned int rsb;
+ unsigned int num_data_blocks;
+ unsigned int data_offs_bits[2];
+ struct gprs_rlc_ul_data_block_info block_info[2];
+};
+
struct gprs_rlc_data {
uint8_t *prepare(size_t block_data_length);
void put_data(const uint8_t *data, size_t len);
@@ -219,6 +243,28 @@
m:1,
li:6;
} __attribute__ ((packed));
+
+struct rlc_li_field_egprs {
+ uint8_t e:1,
+ li:7;
+} __attribute__ ((packed));
+
+struct gprs_rlc_ul_header_egprs_3 {
+ uint8_t r:1,
+ si:1,
+ cv:4,
+ tfi_a:2;
+ uint8_t tfi_b:3,
+ bsn1_a:5;
+ uint8_t bsn1_b:6,
+ cps_a:2;
+ uint8_t cps_b:2,
+ spb:2,
+ rsb:1,
+ pi:1,
+ spare:1,
+ dummy:1;
+} __attribute__ ((packed));
#else
# error "Only little endian headers are supported yet. TODO: add missing structs"
#endif