gsm: add gsm0502_fn2ccch_block()
This API is useful for checking whether a Downlink CCCH block belongs
to PCH or AGCH. We need this API in osmo-bts.git and osmocom-bb.git.
Change-Id: I8cbd31226754e95887358ed83a928e2f567f4cf3
Related: OS#5500
diff --git a/include/osmocom/gsm/gsm0502.h b/include/osmocom/gsm/gsm0502.h
index ac697d9..43ab0b8 100644
--- a/include/osmocom/gsm/gsm0502.h
+++ b/include/osmocom/gsm/gsm0502.h
@@ -105,3 +105,5 @@
uint16_t gsm0502_hop_seq_gen(const struct gsm_time *t,
uint8_t hsn, uint8_t maio,
size_t n, const uint16_t *ma);
+
+int gsm0502_fn2ccch_block(uint32_t fn);
diff --git a/src/gsm/gsm0502.c b/src/gsm/gsm0502.c
index b147406..e9e612a 100644
--- a/src/gsm/gsm0502.c
+++ b/src/gsm/gsm0502.c
@@ -260,3 +260,38 @@
return ma ? ma[mai] : mai;
}
+
+#define CB_FCCH -1
+#define CB_SCH -2
+#define CB_BCCH -3
+#define CB_IDLE -4
+
+/* Clause 7 Table 3 and Figure 8a */
+static const int ccch_block_table[51] = {
+ CB_FCCH, CB_SCH, /* 0..1 */
+ CB_BCCH, CB_BCCH, CB_BCCH, CB_BCCH, /* 2..5: BCCH */
+ 0, 0, 0, 0, /* 6..9: B0 */
+ CB_FCCH, CB_SCH, /* 10..11 */
+ 1, 1, 1, 1, /* 12..15: B1 */
+ 2, 2, 2, 2, /* 16..19: B2 */
+ CB_FCCH, CB_SCH, /* 20..21 */
+ 3, 3, 3, 3, /* 22..25: B3 */
+ 4, 4, 4, 4, /* 26..29: B4 */
+ CB_FCCH, CB_SCH, /* 30..31 */
+ 5, 5, 5, 5, /* 32..35: B5 */
+ 6, 6, 6, 6, /* 36..39: B6 */
+ CB_FCCH, CB_SCH, /* 40..41 */
+ 7, 7, 7, 7, /* 42..45: B7 */
+ 8, 8, 8, 8, /* 46..49: B8 */
+ CB_IDLE /* 50: Idle */
+};
+
+/*! Calculate CCCH block number from the given TDMA frame number.
+ * \param[in] fn TDMA frame number (of first or last burst).
+ * \returns CCCH block number 0..8 or a negative value,
+ * if the given frame number cannot carry CCCH.
+ */
+int gsm0502_fn2ccch_block(uint32_t fn)
+{
+ return ccch_block_table[fn % 51];
+}
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 1e5a7b2..609ee7e 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -111,6 +111,7 @@
gsm0502_calc_paging_group;
gsm0502_fn_remap;
gsm0502_hop_seq_gen;
+gsm0502_fn2ccch_block;
gsm0503_xcch;
gsm0503_rach;