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-rw-r--r--src/osmo-bts-trx/pxxch.c473
1 files changed, 473 insertions, 0 deletions
diff --git a/src/osmo-bts-trx/pxxch.c b/src/osmo-bts-trx/pxxch.c
new file mode 100644
index 00000000..17a7c947
--- /dev/null
+++ b/src/osmo-bts-trx/pxxch.c
@@ -0,0 +1,473 @@
+/*
+ * pxxch.c
+ *
+ * Copyright (c) 2013 Andreas Eversberg <jolly@eversberg.eu>
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/conv.h>
+#include <osmocom/core/crcgen.h>
+
+#include "pxxch.h"
+
+
+/*
+ * GSM PDTCH parity (FIRE code)
+ *
+ * g(x) = (x^23 + 1)(x^17 + x^3 + 1)
+ * = x^40 + x^26 + x^23 + x^17 + x^3 + 1
+ */
+
+const struct osmo_crc64gen_code pxxch_crc40 = {
+ .bits = 40,
+ .poly = 0x0004820009ULL,
+ .init = 0x0000000000ULL,
+ .remainder = 0xffffffffffULL,
+};
+
+
+/*
+ * GSM PDTCH CS-2, CS-3 parity
+ *
+ * g(x) = x^16 + x^12 + x^5 + 1
+ */
+
+const struct osmo_crc16gen_code pdtch_crc16 = {
+ .bits = 16,
+ .poly = 0x1021,
+ .init = 0x0000,
+ .remainder = 0xffff,
+};
+
+
+/*
+ * GSM PDTCH convolutional coding
+ *
+ * G_0 = 1 + x^3 + x^4
+ * G_1 = 1 + x + x^3 + x^4
+ */
+
+static const uint8_t conv_cs1_next_output[][2] = {
+ { 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+ { 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+ { 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+ { 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+};
+
+static const uint8_t conv_cs1_next_state[][2] = {
+ { 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
+ { 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+ { 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
+ { 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+};
+
+static const struct osmo_conv_code conv_cs1 = {
+ .N = 2,
+ .K = 5,
+ .len = 224,
+ .next_output = conv_cs1_next_output,
+ .next_state = conv_cs1_next_state,
+};
+
+static const uint8_t conv_cs2_next_output[][2] = {
+ { 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+ { 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+ { 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+ { 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+};
+
+static const uint8_t conv_cs2_next_state[][2] = {
+ { 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
+ { 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+ { 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
+ { 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+};
+
+static const struct osmo_conv_code conv_cs2 = {
+ .N = 2,
+ .K = 5,
+ .len = 290,
+ .next_output = conv_cs2_next_output,
+ .next_state = conv_cs2_next_state,
+};
+
+static const uint8_t conv_cs3_next_output[][2] = {
+ { 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+ { 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+ { 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+ { 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+};
+
+static const uint8_t conv_cs3_next_state[][2] = {
+ { 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
+ { 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+ { 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
+ { 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+};
+
+static const struct osmo_conv_code conv_cs3 = {
+ .N = 2,
+ .K = 5,
+ .len = 334,
+ .next_output = conv_cs3_next_output,
+ .next_state = conv_cs3_next_state,
+};
+
+
+/*
+ * GSM PxxCH interleaving and burst mapping
+ *
+ * Interleaving:
+ *
+ * Given 456 coded input bits, form 4 blocks of 114 bits:
+ *
+ * i(B, j) = c(n, k) k = 0, ..., 455
+ * n = 0, ..., N, N + 1, ...
+ * B = B_0 + 4n + (k mod 4)
+ * j = 2(49k mod 57) + ((k mod 8) div 4)
+ *
+ * Mapping on Burst:
+ *
+ * e(B, j) = i(B, j)
+ * e(B, 59 + j) = i(B, 57 + j) j = 0, ..., 56
+ * e(B, 57) = h_l(B)
+ * e(B, 58) = h_n(B)
+ *
+ * Where hl(B) and hn(B) are bits in burst B indicating flags.
+ */
+
+static void
+pxxch_deinterleave(sbit_t *cB, sbit_t *iB)
+{
+ int j, k, B;
+
+ for (k=0; k<456; k++) {
+ B = k & 3;
+ j = 2 * ((49 * k) % 57) + ((k & 7) >> 2);
+ cB[k] = iB[B * 114 + j];
+ }
+}
+
+static void
+pxxch_interleave(ubit_t *cB, ubit_t *iB)
+{
+ int j, k, B;
+
+ for (k=0; k<456; k++) {
+ B = k & 3;
+ j = 2 * ((49 * k) % 57) + ((k & 7) >> 2);
+ iB[B * 114 + j] = cB[k];
+ }
+}
+
+static void
+pxxch_burst_unmap(sbit_t *iB, sbit_t *eB, sbit_t *hl, sbit_t *hn)
+{
+ memcpy(iB, eB, 57);
+ memcpy(iB+57, eB+59, 57);
+
+ if (hl)
+ *hl = eB[57];
+
+ if (hn)
+ *hn = eB[58];
+}
+
+static void
+pxxch_burst_map(ubit_t *iB, ubit_t *eB, ubit_t *hl, ubit_t *hn)
+{
+ memcpy(eB, iB, 57);
+ memcpy(eB+59, iB+57, 57);
+
+ if (hl)
+ eB[57] = *hl;
+ if (hn)
+ eB[58] = *hn;
+}
+
+static ubit_t pdtch_hl_hn[4][8] = {
+ { 1,1, 1,1, 1,1, 1,1 },
+ { 1,1, 0,0, 1,0, 0,0 },
+ { 0,0, 1,0, 0,0, 0,1 },
+ { 0,0, 0,1, 0,1, 1,0 },
+};
+
+static ubit_t usf2six[8][6] = {
+ { 0,0,0, 0,0,0 },
+ { 0,0,1, 0,1,1 },
+ { 0,1,0, 1,1,0 },
+ { 0,1,1, 1,0,1 },
+ { 1,0,0, 1,0,1 },
+ { 1,0,1, 1,1,0 },
+ { 1,1,0, 0,1,1 },
+ { 1,1,1, 0,0,0 },
+};
+
+static ubit_t usf2twelve[8][12] = {
+ { 0,0,0, 0,0,0, 0,0,0, 0,0,0 },
+ { 0,0,0, 0,1,1, 0,1,1, 1,0,1 },
+ { 0,0,1, 1,0,1, 1,1,0, 1,1,0 },
+ { 0,0,1, 1,1,0, 1,0,1, 0,1,1 },
+ { 1,1,0, 1,0,0, 0,0,1, 0,1,1 },
+ { 1,1,0, 1,1,1, 0,1,0, 1,1,0 },
+ { 1,1,1, 0,0,1, 1,1,1, 1,0,1 },
+ { 1,1,1, 0,1,0, 1,0,0, 0,0,0 },
+};
+
+static uint8_t puncture_cs2[588] = {
+ 0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
+ 0,0,0,1, 0,0,0,1, 0,0,0,1
+};
+
+static uint8_t puncture_cs3[676] = {
+ 0,0,0,0,0,0, 0,0,0,0,0,0, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
+ 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,0
+};
+
+int
+pdch_decode(uint8_t *l2_data, sbit_t *bursts, uint8_t *usf_p)
+{
+ sbit_t iB[456], cB[676], hl_hn[8];
+ ubit_t conv[456];
+ int i, j, k, rv, best, cs, usf;
+
+ for (i=0; i<4; i++)
+ pxxch_burst_unmap(&iB[i * 114], &bursts[i * 116], hl_hn + i*2,
+ hl_hn + i*2 + 1);
+
+ for (i=0, best=0, cs=1; i<4; j++) {
+ for (j=0, k=0; j<4; j++) {
+ if (pdtch_hl_hn[i][j] == hl_hn[j])
+ k++;
+ }
+ if (k > best)
+ cs = i+1;
+ }
+
+ pxxch_deinterleave(cB, iB);
+
+ switch (cs) {
+ case 1:
+ osmo_conv_decode(&conv_cs1, cB, conv);
+
+ rv = osmo_crc64gen_check_bits(&pxxch_crc40, conv, 184,
+ conv+184);
+ if (rv)
+ return -1;
+
+ osmo_ubit2pbit_ext(l2_data, 0, conv, 0, 184, 1);
+
+ return 23;
+ case 2:
+ for (i=587, j=455; i>=0; i++)
+ if (!puncture_cs2[i])
+ cB[i] = cB[j--];
+ else
+ cB[i] = 0;
+
+ osmo_conv_decode(&conv_cs2, cB, conv);
+
+ for (i=0, best=0, usf=0; i<8; j++) {
+ for (j=0, k=0; j<6; j++) {
+ if (usf2six[i][j] == conv[j])
+ k++;
+ }
+ if (k > best)
+ usf = i;
+ }
+
+ conv[3] = (usf >> 2) & 1;
+ conv[4] = (usf >> 1) & 1;
+ conv[5] = usf & 1;
+ if (usf_p)
+ *usf_p = usf;
+
+ rv = osmo_crc64gen_check_bits(&pxxch_crc40, conv+3, 271,
+ conv+3+271);
+ if (rv)
+ return -1;
+
+ osmo_ubit2pbit_ext(l2_data, 0, conv, 0, 271, 1);
+
+ return 34;
+ case 3:
+ for (i=675, j=455; i>=0; i++)
+ if (!puncture_cs3[i])
+ cB[i] = cB[j--];
+ else
+ cB[i] = 0;
+
+ osmo_conv_decode(&conv_cs3, cB, conv);
+
+ for (i=0, best=0, usf=0; i<8; j++) {
+ for (j=0, k=0; j<6; j++) {
+ if (usf2six[i][j] == conv[j])
+ k++;
+ }
+ if (k > best)
+ usf = i;
+ }
+
+ conv[3] = (usf >> 2) & 1;
+ conv[4] = (usf >> 1) & 1;
+ conv[5] = usf & 1;
+ if (usf_p)
+ *usf_p = usf;
+
+ rv = osmo_crc64gen_check_bits(&pxxch_crc40, conv+3, 315,
+ conv+3+315);
+ if (rv)
+ return -1;
+
+ osmo_ubit2pbit_ext(l2_data, 0, conv, 0, 315, 1);
+
+ return 40;
+ case 4:
+ for (i=0; i<456;i++)
+ conv[i] = (cB[i] < 0) ? 1:0;
+
+ for (i=0, best=0, usf=0; i<8; j++) {
+ for (j=0, k=0; j<12; j++) {
+ if (usf2twelve[i][j] == conv[j])
+ k++;
+ }
+ if (k > best)
+ usf = i;
+ }
+
+ conv[9] = (usf >> 2) & 1;
+ conv[10] = (usf >> 1) & 1;
+ conv[11] = usf & 1;
+ if (usf_p)
+ *usf_p = usf;
+
+ rv = osmo_crc64gen_check_bits(&pxxch_crc40, conv+9, 431,
+ conv+9+431);
+ if (rv)
+ return -1;
+
+ osmo_ubit2pbit_ext(l2_data, 0, conv, 0, 431, 1);
+
+ return 54;
+ }
+
+ return -1;
+}
+
+int
+pdtch_encode(ubit_t *bursts, uint8_t *l2_data, uint8_t l2_len)
+{
+ ubit_t iB[456], cB[676], *hl_hn;
+ ubit_t conv[334];
+ int i, j, usf;
+
+ switch (l2_len) {
+ case 23:
+ osmo_pbit2ubit_ext(conv, 0, l2_data, 0, 184, 1);
+
+ osmo_crc64gen_set_bits(&pxxch_crc40, conv, 184, conv+184);
+
+ osmo_conv_encode(&conv_cs1, conv, cB);
+
+ hl_hn = pdtch_hl_hn[0];
+
+ break;
+ case 34:
+ osmo_pbit2ubit_ext(conv, 3, l2_data, 0, 271, 1);
+ usf = (conv[3] << 2) | (conv[4] << 1) | conv[5];
+
+ osmo_crc16gen_set_bits(&pdtch_crc16, conv+3, 271, conv+3+271);
+
+ memcpy(conv, usf2six[usf], 6);
+
+ osmo_conv_encode(&conv_cs2, conv, cB);
+
+ for (i=0, j=0; i<588; i++)
+ if (!puncture_cs2[i])
+ cB[j++] = cB[i];
+
+ hl_hn = pdtch_hl_hn[1];
+
+ break;
+ case 40:
+ osmo_pbit2ubit_ext(conv, 3, l2_data, 0, 315, 1);
+ usf = (conv[3] << 2) | (conv[4] << 1) | conv[5];
+
+ osmo_crc16gen_set_bits(&pdtch_crc16, conv+3, 315, conv+3+315);
+
+ memcpy(conv, usf2six[usf], 6);
+
+ osmo_conv_encode(&conv_cs3, conv, cB);
+
+ for (i=0, j=0; i<676; i++)
+ if (!puncture_cs3[i])
+ cB[j++] = cB[i];
+
+ hl_hn = pdtch_hl_hn[2];
+
+ break;
+ case 54:
+ osmo_pbit2ubit_ext(cB, 9, l2_data, 0, 431, 1);
+ usf = (cB[9] << 2) | (cB[10] << 1) | conv[11];
+
+ osmo_crc16gen_set_bits(&pdtch_crc16, cB+9, 431, cB+9+431);
+
+ memcpy(cB, usf2twelve[usf], 12);
+
+ hl_hn = pdtch_hl_hn[3];
+
+ break;
+ default:
+ return -1;
+ }
+
+ pxxch_interleave(cB, iB);
+
+ for (i=0; i<4; i++)
+ pxxch_burst_map(&iB[i * 114], &bursts[i * 116], hl_hn + i*2,
+ hl_hn + i*2 + 1);
+
+ return 0;
+}
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