gsmstack: add new unfinished GSM burst/channel demultiplex

This is some unfinished work on a new codebase for 'proper'
demultiplex of all the various physical and logical channel
types.

Basically this includes everything needed to get from the
differential-decoded bursts up to the MAC blocks that can
be passed up to layer 2.

1 files changed, 105 insertions, 0 deletions

diff --git a/gsmstack/get_lctype.c b/gsmstack/get_lctype.c
new file mode 100644
index 0000000..953b56d
--- /dev/null
+++ b/gsmstack/get_lctype.c
@@ -0,0 +1,105 @@
+
+/* helper routines to determine the logical channel type based on
+ * physical channel configuration and frame number */
+
+#include "gsmstack.h"
+#include "get_lctype.h"
+
+#define GSM_FN_51	(fn / 51)
+
+#define GSM_TC(fn)	((fn / 51) % 8)
+
+
+/* parameters determined from CCCH_CONF (octet 2 of control channel description
+ * in System Information Type 3:
+ * BS_CC_CHANS defines if we have CCCH on ts 2/4/6
+ * BS_CCCH_SDCCH_COMB defines if we have SDCCH/8 SACCH/C8 on TS0 
+ * BS_AG_BLKS_RES defines which CCCH blocks are reserved for AGCH 
+ * if BCCH Ext. is used, BS_AS_BLKS_RES has to be non-zero
+ */
+
+static int get_lctype_for_ccch(unsigned int fnr)
+{
+	unsigned int fnr51 = GSM_FN_51(fnr);
+	int lc_type;
+
+	if (fnr51 % 10 == 0)
+		lc_type = GSM_LCHAN_FCCH;
+	else if (fnr51 % 10 == 1)
+		lc_type = GSM_LCHAN_SCH;
+	else if (fnr51 >= 2 && fnr_mod_51 <= 5)
+		lc_type = GSM_LCHAN_BCCH;
+	else if (fnr51 >= 6 && fnr51 <= 9) {
+		if (flags & CCCH_F_BCCH_EXT)
+			lc_type = GSM_LCHAN_BCCH;
+		else
+			lc_ctype = GSM_LCHAN_PCH;
+	} else
+		lc_ctype = GSM_LCHAN_PCH;
+
+	/* FIXME: what about AGCH ? */
+	/* FIXME: what about NCH ? */
+	/* FIXME: what about CBCH ? */
+
+	return lc_ctype;
+}
+
+static int get_lctype_for_sdcch8(unsigned int fnr)
+{
+	unsigned int fnr51 = GSM_FN_51(fnr);
+	unsigned int fnr102 = fnr % 102;
+	int lc_type;
+
+	/* the lower 32 bursts are evenly divided between SDCCH8 0..7 */
+	if (fnr51 % < 32) {
+		lc_type = GSM_LCHAN_SDCCH8;
+		subc = fnr51 / 4;
+	} else {
+		/* the upper 16 bursts are bundles of four bursts for 
+		 * alternating either SACCH0..3 or SACCH4..7 */
+		lc_type = GSM_LCHAN_SACCH8C;
+		subc = (fnr51 - 32) / 4;
+		if (fnr102 > 50)
+			subc += 4;
+	}
+
+	return lc_type;
+}
+
+static int get_lctype_for_tch_f(unsigned int fnr)
+{
+	unsigned int fnr52 = fnr % 52;
+	int lc_type = GSM_LCHAN_TCH;
+
+	/* only burst number 12 and 51 are be SACCH */
+	if (fnr52 == 12 || fnr52 == 51)
+		lc_ctype = GSM_LCHAN_SACCH;
+	/* burst number 26 and 39 are empty (for measurements) */
+	else if (fnr52 == 26 || fnr52 == 39)
+		lc_ctype = GSM_LCHAN_NONE;
+
+	return lc_type;
+}
+
+int get_lctype(struct gsm_phys_chan *pchan, int fnr)
+{
+	switch (pchan->config) {
+	case GSM_PCHAN_CCCH:
+		return get_lctype_for_ccch(fnr);
+		break;
+	case GSM_PCHAN_TCH_F:
+		return get_lctype_for_tch_f(fnr);
+		break;
+	case GSM_PCHAN_SDCCH8_SACCH8C:
+		return get_lctype_for_sdcch8(fnr);
+		break;
+	}
+
+	return -EINVAL;
+}
+
+struct gsm_logi_chan *get_lchan(struct gsm_phys_chan *pchan, int fnr)
+{
+	int lctype = get_lctype(pchan, fnr);
+	return pchan->logi_chan[lctype];
+}