edge: Add encoder for downlink RLC data blocks
Currently the (GPRS) RLC block encoding is done by setting the
header fields directly in gprs_rlcmac_dl_tbf::create_new_bsn.
This is much more complex with EGPRS, since the data fields are
not byte aligned, the header formats depend on the header type,
and the mapping of bits to bytes is LSB first.
This commit adds Encoding::rlc_write_dl_data_header which writes
the header according to the given gprs_rlc_data_header structure.
Encoding::rlc_copy_from_aligned_buffer is also added to copy
byte sequences into the message.
Note that the actual encoding of data units is not yet present.
Sponsored-by: On-Waves ehf
diff --git a/src/encoding.cpp b/src/encoding.cpp
index fdc8d0a..0756ffc 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -25,6 +25,9 @@
#include <tbf.h>
#include <gprs_debug.h>
+#include <errno.h>
+#include <string.h>
+
// GSM 04.08 9.1.18 Immediate assignment
int Encoding::write_immediate_assignment(
struct gprs_rlcmac_bts *bts,
@@ -631,3 +634,120 @@
return wp;
}
+int Encoding::rlc_write_dl_data_header(const struct gprs_rlc_data_info *rlc,
+ uint8_t *data)
+{
+ struct gprs_rlc_dl_header_egprs_3 *egprs3;
+ struct rlc_dl_header *gprs;
+ unsigned int e_fbi_header;
+ GprsCodingScheme cs = rlc->cs;
+
+ switch(cs.headerTypeData()) {
+ case GprsCodingScheme::HEADER_GPRS_DATA:
+ gprs = static_cast<struct rlc_dl_header *>
+ ((void *)data);
+
+ gprs->usf = rlc->usf;
+ gprs->s_p = rlc->es_p != 0 ? 1 : 0;
+ gprs->rrbp = rlc->rrbp;
+ gprs->pt = 0;
+ gprs->tfi = rlc->tfi;
+ gprs->pr = rlc->pr;
+
+ gprs->fbi = rlc->block_info[0].cv == 0;
+ gprs->e = rlc->block_info[0].e;
+ gprs->bsn = rlc->block_info[0].bsn;
+ break;
+
+ case GprsCodingScheme::HEADER_EGPRS_DATA_TYPE_3:
+ egprs3 = static_cast<struct gprs_rlc_dl_header_egprs_3 *>
+ ((void *)data);
+
+ egprs3->usf = rlc->usf;
+ egprs3->es_p = rlc->es_p;
+ egprs3->rrbp = rlc->rrbp;
+ egprs3->tfi_a = rlc->tfi >> 0; /* 1 bit LSB */
+ egprs3->tfi_b = rlc->tfi >> 1; /* 4 bits */
+ egprs3->pr = rlc->pr;
+ egprs3->cps = rlc->cps;
+
+ egprs3->bsn1_a = rlc->block_info[0].bsn >> 0; /* 2 bits LSB */
+ egprs3->bsn1_b = rlc->block_info[0].bsn >> 2; /* 8 bits */
+ egprs3->bsn1_c = rlc->block_info[0].bsn >> 10; /* 1 bit */
+
+ egprs3->spb = rlc->block_info[0].spb;
+
+ e_fbi_header = rlc->block_info[0].e ? 0x01 : 0;
+ e_fbi_header |= rlc->block_info[0].cv == 0 ? 0x02 : 0; /* FBI */
+ e_fbi_header <<= 7;
+ data[3] = (data[3] & 0b01111111) | (e_fbi_header >> 0);
+ data[4] = (data[4] & 0b11111110) | (e_fbi_header >> 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,
+ "Encoding of uplink %s data blocks not yet supported.\n",
+ cs.name());
+ return -ENOTSUP;
+ };
+
+ return 0;
+}
+
+/**
+ * \brief Copy LSB bitstream RLC data block from 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 Encoding::rlc_copy_from_aligned_buffer(
+ const struct gprs_rlc_data_info *rlc,
+ unsigned int data_block_idx,
+ uint8_t *dst, const uint8_t *buffer)
+{
+ unsigned int hdr_bytes;
+ unsigned int extra_bits;
+ unsigned int i;
+
+ uint8_t c, last_c;
+ const uint8_t *src;
+ const struct gprs_rlc_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] / 8;
+ extra_bits = (rlc->data_offs_bits[data_block_idx] % 8);
+
+ if (extra_bits == 0) {
+ /* It is aligned already */
+ memmove(dst + hdr_bytes, buffer, rdbi->data_len);
+ return rdbi->data_len;
+ }
+
+ src = buffer;
+ dst = dst + hdr_bytes;
+ last_c = *dst << (8 - extra_bits);
+
+ for (i = 0; i < rdbi->data_len; i++) {
+ c = src[i];
+ *(dst++) = (last_c >> (8 - extra_bits)) | (c << extra_bits);
+ last_c = c;
+ }
+
+ /* overwrite the lower extra_bits */
+ *dst = (*dst & (0xff << extra_bits)) | (last_c >> (8 - extra_bits));
+
+ return rdbi->data_len;
+}