--- a/doc/HR-codec-library	Fri Mar 20 03:58:33 2026 +0000
+++ b/doc/HR-codec-library	Fri Mar 20 04:27:04 2026 +0000
@@ -418,3 +418,25 @@
 frame into a SID frame with the same R0 and LPC parameters.  It is logically
 equivalent to gsmhr_ts101318_set_sid_codeword(), but operates on the array of
 parameters form, rather than TS 101 318 packed format.
+
+Public constant definitions
+===========================
+
+Our public header file <tw_gsmhr.h> provides these constant definitions, which
+should be self-explanatory:
+
+#define	GSMHR_NUM_PARAMS	18	/* actual codec parameters */
+#define	GSMHR_NUM_PARAMS_ENC	20	/* output from the encoder */
+#define	GSMHR_NUM_PARAMS_DEC	22	/* input to the decoder */
+
+#define	GSMHR_FRAME_LEN_RPF	14	/* raw packed format */
+#define	GSMHR_FRAME_LEN_5993	15	/* RFC 5993 and TW-TS-002 */
+
+Public const data items
+=======================
+
+The spec-defined decoder homing frame for GSM-HR is provided in both native
+(array of parameters) and packed (TS 101 318) formats:
+
+extern const int16_t gsmhr_dhf_params[GSMHR_NUM_PARAMS];
+extern const uint8_t gsmhr_dhf_ts101318[GSMHR_FRAME_LEN_RPF];