--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/cs/layer1/cfile/l1_tch_tap.c	Tue Dec 13 02:44:01 2022 +0000
@@ -0,0 +1,178 @@
+/*
+ * This module is a FreeCalypso addition; it contains code implementing
+ * our TCH tap functional additions: TCH downlink capture and TCH uplink
+ * play.
+ */
+
+#include "l1_macro.h"
+#include "l1_confg.h"
+#include "l1_types.h"
+#include "sys_types.h"
+#include <string.h>
+#include "l1_const.h"
+
+#if TESTMODE
+  #include "l1tm_defty.h"
+#endif
+#if (AUDIO_TASK == 1)
+  #include "l1audio_const.h"
+  #include "l1audio_cust.h"
+  #include "l1audio_defty.h"
+#endif
+#if (L1_GTT == 1)
+  #include "l1gtt_const.h"
+  #include "l1gtt_defty.h"
+#endif
+#if (L1_MIDI == 1)
+  #include "l1midi_defty.h"
+#endif
+#include "l1_defty.h"
+
+#include "l1_varex.h"
+#include "l1_trace.h"
+#include "tch_tap_proto.h"
+
+T_RVT_USER_ID tch_tap_rvt_id;
+BOOL tch_dl_sniff_mode, tch_ul_play_mode;
+
+void tch_send_downlink_bits(API *dsp_buffer, UWORD8 nwords, UWORD8 chan_mode,
+			    UWORD8 fn_mod_104)
+{
+	UWORD16 size;
+	T_RVT_BUFFER buf;
+	T_RVT_RET rc;
+	UINT8 *dp;
+	UWORD16 apiword;
+	int i;
+
+	size = nwords * 2 + 3;
+	rc = rvt_mem_alloc(tch_tap_rvt_id, size, &buf);
+	if (rc != RVT_OK)
+		return;
+	dp = buf;
+	*dp++ = TCH_DLBITS_NEW_IND;
+	*dp++ = chan_mode;
+	*dp++ = fn_mod_104;
+	for (i = 0; i < nwords; i++) {
+		apiword = dsp_buffer[i];
+		*dp++ = apiword >> 8;
+		*dp++ = apiword;
+	}
+	rvt_send_trace_no_cpy(buf, tch_tap_rvt_id, size, RVT_BINARY_FORMAT);
+}
+
+static void send_tch_ulbits_conf(void)
+{
+	T_RVT_BUFFER buf;
+	T_RVT_RET rc;
+
+	rc = rvt_mem_alloc(tch_tap_rvt_id, 1, &buf);
+	if (rc == RVT_OK) {
+		buf[0] = TCH_ULBITS_CONF;
+		rvt_send_trace_no_cpy(buf, tch_tap_rvt_id, 1,
+					RVT_BINARY_FORMAT);
+	}
+}
+
+#define	UPLINK_QUEUE_SIZE	5
+#define	WORDS_PER_ENTRY		17
+
+static UWORD16 uplink_data[UPLINK_QUEUE_SIZE][WORDS_PER_ENTRY];
+static volatile int ul_read_ptr, ul_write_ptr;
+
+void tchf_substitute_uplink(API *dsp_buffer)
+{
+	int read_ptr;
+	int i;
+
+	read_ptr = ul_read_ptr;
+	if (read_ptr == ul_write_ptr) {
+		/* no uplink substitution */
+		l1s_dsp_com.dsp_ndb_ptr->d_tch_mode &= ~B_PLAY_UL;
+		tch_ul_play_mode = FALSE;
+		return;
+	}
+	for (i = 0; i < WORDS_PER_ENTRY; i++)
+		dsp_buffer[i+3] = uplink_data[read_ptr][i];
+	// Fill data block Header...
+	dsp_buffer[0] = (1 << B_BLUD);		// 1st word: Set B_BLU bit.
+	dsp_buffer[1] = 0;			// 2nd word: cleared.
+	dsp_buffer[2] = 0;			// 3rd word: cleared.
+	l1s_dsp_com.dsp_ndb_ptr->d_tch_mode |= B_PLAY_UL;
+	/* advance the read pointer and send TCH_ULBITS_CONF */
+	read_ptr++;
+	if (read_ptr >= UPLINK_QUEUE_SIZE)
+		read_ptr = 0;
+	ul_read_ptr = read_ptr;
+	send_tch_ulbits_conf();
+}
+
+static void handle_tch_ulbits_req(T_RVT_BUFFER pkt)
+{
+	int write_ptr, write_next, i;
+	UINT8 *sp;
+
+	write_ptr = ul_write_ptr;
+	write_next = write_ptr + 1;
+	if (write_next >= UPLINK_QUEUE_SIZE)
+		write_next = 0;
+	if (write_next == ul_read_ptr)	/* queue full */
+		return;
+	sp = pkt + 1;
+	for (i = 0; i < WORDS_PER_ENTRY; i++) {
+		uplink_data[write_ptr][i] = (sp[0] << 8) | sp[1];
+		sp += 2;
+	}
+	ul_write_ptr = write_next;
+	tch_ul_play_mode = TRUE;
+}
+
+static void handle_tch_config_req(T_RVT_BUFFER pkt)
+{
+	UWORD8 config;
+	T_RVT_BUFFER buf;
+	T_RVT_RET rc;
+
+	config = pkt[1] & 0x01;
+	tch_dl_sniff_mode = config;
+
+	/* send TCH_CONFIG_CONF response */
+	rc = rvt_mem_alloc(tch_tap_rvt_id, 2, &buf);
+	if (rc == RVT_OK) {
+		buf[0] = TCH_CONFIG_CONF;
+		buf[1] = config;
+		rvt_send_trace_no_cpy(buf, tch_tap_rvt_id, 2,
+					RVT_BINARY_FORMAT);
+	}
+}
+
+/*
+ * The following function is the callback registered with RVT; it gets
+ * called in RVT HISR context.
+ */
+static void tch_rvt_input_callback(T_RVT_BUFFER pkt, UINT16 pktlen)
+{
+	if (pktlen < 1)
+		return;
+	switch (pkt[0]) {
+	case TCH_CONFIG_REQ:
+		if (pktlen != 2)
+			return;
+		handle_tch_config_req(pkt);
+		break;
+	case TCH_ULBITS_REQ:
+		if (pktlen < 34)
+			return;
+		handle_tch_ulbits_req(pkt);
+		break;
+	}
+}
+
+void tch_tap_init(void)
+{
+	rvt_register_id("TCH", &tch_tap_rvt_id, tch_rvt_input_callback);
+	tch_dl_sniff_mode = FALSE;
+	tch_ul_play_mode = FALSE;
+	ul_read_ptr = 0;
+	ul_write_ptr = 0;
+}