Introduce new amr.[ch] for AMR related functions

1 files changed, 115 insertions, 0 deletions

diff --git a/src/common/amr.c b/src/common/amr.c
new file mode 100644
index 00000000..eeb6e7f2
--- /dev/null
+++ b/src/common/amr.c
@@ -0,0 +1,115 @@
+#include <stdint.h>
+#include <errno.h>
+
+#include <osmocom/core/logging.h>
+
+#include <osmo-bts/logging.h>
+#include <osmo-bts/amr.h>
+
+void amr_log_mr_conf(int ss, int logl, const char *pfx,
+		     struct amr_multirate_conf *amr_mrc)
+{
+	int i;
+
+	LOGP(ss, logl, "%s AMR MR Conf: num_modes=%u",
+		pfx, amr_mrc->num_modes);
+
+	for (i = 0; i < amr_mrc->num_modes; i++)
+		LOGPC(ss, logl, ", mode[%u] = %u/%u/%u",
+			i, amr_mrc->mode[i].mode, amr_mrc->mode[i].threshold,
+			amr_mrc->mode[i].hysteresis);
+	LOGPC(ss, logl, "\n");
+}
+
+
+/* parse a GSM 04.08 MultiRate Config IE (10.5.2.21aa) in a more
+ * comfortable internal data structure */
+int amr_parse_mr_conf(struct amr_multirate_conf *amr_mrc,
+		      const uint8_t *mr_conf, unsigned int len)
+{
+	uint8_t mr_version = mr_conf[0] >> 5;
+	uint8_t num_codecs = 0;
+	int i, j = 0;
+
+	if (mr_version != 1) {
+		LOGP(DRSL, LOGL_ERROR, "AMR Multirate Version %u unknonw\n",
+			mr_version);
+		goto ret_einval;
+	}
+
+	/* check number of active codecs */
+	for (i = 0; i < 8; i++) {
+		if (mr_conf[1] & (1 << i))
+			num_codecs++;
+	}
+
+	/* check for minimum length */
+	if (num_codecs == 0 ||
+	    (num_codecs == 1 && len < 2) ||
+	    (num_codecs == 2 && len < 4) ||
+	    (num_codecs == 3 && len < 5) ||
+	    (num_codecs == 4 && len < 6) ||
+	    (num_codecs > 4)) {
+		LOGP(DRSL, LOGL_ERROR, "AMR Multirate with %u modes len=%u "
+		     "not possible\n", num_codecs, len);
+		goto ret_einval;
+	}
+
+	/* copy the first two octets of the IE */
+	amr_mrc->gsm48_ie[0] = mr_conf[0];
+	amr_mrc->gsm48_ie[1] = mr_conf[1];
+
+	amr_mrc->num_modes = num_codecs;
+
+	for (i = 0; i < 8; i++) {
+		if (mr_conf[1] & (1 << i)) {
+			amr_mrc->mode[j++].mode = i;
+		}
+	}
+
+	if (num_codecs >= 2) {
+		amr_mrc->mode[0].threshold = mr_conf[1] & 0x3F;
+		amr_mrc->mode[0].hysteresis = mr_conf[2] >> 4;
+	}
+	if (num_codecs >= 3) {
+		amr_mrc->mode[1].threshold =
+			((mr_conf[2] & 0xF) << 2) | (mr_conf[3] >> 6);
+		amr_mrc->mode[1].hysteresis = (mr_conf[3] >> 2) & 0x7;
+	}
+	if (num_codecs >= 4) {
+		amr_mrc->mode[3].threshold =
+			((mr_conf[3] & 0x3) << 4) | (mr_conf[4] >> 4);
+		amr_mrc->mode[3].hysteresis = mr_conf[4] & 0xF;
+	}
+
+	return num_codecs;
+
+ret_einval:
+	return -EINVAL;
+}
+
+
+unsigned int amr_get_initial_mode(struct gsm_lchan *lchan)
+{
+	struct amr_multirate_conf *amr_mrc = &lchan->tch.amr_mr;
+
+	if (lchan->mr_conf.icmi) {
+		/* initial mode given, coding in TS 05.09 3.4.1 */
+		return amr_mrc->mode[lchan->mr_conf.smod].mode;
+	} else {
+		/* implicit rule according to TS 05.09 Chapter 3.4.3 */
+		switch (amr_mrc->num_modes) {
+		case 2:
+		case 3:
+			/* return the most robust */
+			return amr_mrc->mode[0].mode;
+		case 4:
+			/* return the second-most robust */
+			return amr_mrc->mode[1].mode;
+		case 1:
+		default:
+			/* return the only mode we have */
+			return amr_mrc->mode[0].mode;
+		}
+	}
+}