--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sw/mcsi-rxtx/tx_func.c	Mon Oct 28 06:34:42 2024 +0000
@@ -0,0 +1,48 @@
+/*
+ * Here we implement basic Tx functions: emitting an uplink sample stream
+ * to Calypso MCSI via the FPGA.
+ */
+
+#include <sys/types.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+extern int target_fd;
+
+u_short pcm_fill_word;
+
+static void
+do_idle_fill(buf)
+	u_short *buf;
+{
+	unsigned n;
+
+	for (n = 0; n < 160; n++)
+		buf[n] = pcm_fill_word;
+}
+
+static void
+emit_uart_output(samples)
+	u_short *samples;
+{
+	u_char bytes[320], *dp;
+	unsigned n, samp;
+
+	dp = bytes;
+	for (n = 0; n < 160; n++) {
+		samp = samples[n];
+		*dp++ = samp;
+		*dp++ = samp >> 8;
+	}
+	write(target_fd, bytes, 320);
+}
+
+void
+transmit_20ms_block()
+{
+	u_short tx_samples[160];
+
+	do_idle_fill(tx_samples);
+	emit_uart_output(tx_samples);
+}