Add read-only cassette emulation to IBM 5150 PC. Patch from JohnElliott.

src/cassette.c

@@ -0,0 +1,186 @@
+/************************************************************************
+
+    PCem: IBM 5150 Cassette support
+
+    Copyright (C) 2019  John Elliott <seasip.webmaster@gmail.com>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*************************************************************************/
+
+#include <stdlib.h>
+#include "ibm.h"
+#include "cpu.h"
+#include "device.h"
+#include "pzx.h"
+
+char cassettefn[256];
+
+typedef struct cassette_t 
+{
+	uint8_t motor;		/* Motor status */
+	pzxfile_t pzx;
+	int cycles_last;	/* Cycle count at last cassette poll */
+
+} cassette_t;
+
+extern device_t cassette_device;
+
+
+static cassette_t *st_cas;
+
+
+
+#define CAS_LOG(x) pclog x
+// #define CAS_LOG(x) 
+
+
+/* The PCem CPU uses IBM cycles (4.77MHz). PZX uses Spectrum cycles (3.5MHz)
+ * so scale accordingly. */
+static int32_t pzx_cycles(int32_t pc)
+{
+	double d = pc;
+
+	return (int32_t)(((d * 3.5) / 4.772728) + 0.5);
+}
+
+void cassette_eject(void)
+{
+	if (st_cas->pzx.input)
+	{
+		pzx_close(&st_cas->pzx);
+	}
+	cassettefn[0] = 0;
+}
+
+void cassette_load(const char *filename)
+{
+	FILE *fp;
+	unsigned char magic[8];
+
+	if (!filename) return;
+
+	fp = fopen(filename, "rb");
+	if (!fp)
+	{
+		/* Warn user? */
+		CAS_LOG(("Failed to open cassette input %s\n", filename));
+		return;
+	}
+	memset(magic, 0, sizeof(magic));
+	fread(magic, 1, sizeof(magic), fp);	
+
+	/* Check for PZX signature. In due course support could be added for
+	 * other formats like TZX */
+	if (!memcmp(magic, "PZXT", 4))
+	{
+		const char *result;
+
+		result = pzx_open(&st_cas->pzx, fp);
+
+		if (result)
+		{
+			CAS_LOG(("Failed to open %s as PZX: %s\n",
+				filename, result));
+			fclose(fp);
+			return;			
+		}
+		strcpy(cassettefn, filename);
+	}
+}
+
+
+uint8_t cassette_input(void)
+{
+	int ticks;
+
+	/* While motor is off, result is loopback */
+	if (!st_cas->motor)
+	{
+		return ppispeakon;
+	}
+	/* If there is no tapefile open don't try to extract data */
+	if (st_cas->pzx.input == NULL) return 0;
+	/* Otherwise see how many ticks there have been since the last input */
+	if (st_cas->cycles_last == -1) 
+	{
+		st_cas->cycles_last = cycles;
+	}
+	if (cycles <= st_cas->cycles_last)
+	{
+		ticks = (st_cas->cycles_last - cycles);
+	}
+	else
+	{
+		ticks = (st_cas->cycles_last + (cpu_get_speed() / 100) - cycles);
+	}
+	st_cas->cycles_last = cycles;
+
+	return pzx_advance(&st_cas->pzx, pzx_cycles(ticks));	
+}
+
+
+
+void cassette_set_motor(uint8_t on)
+{
+	if (on && !st_cas->motor)
+	{
+		CAS_LOG(("Start cassette motor\n"));
+		st_cas->cycles_last = -1;
+	}
+	if (st_cas->motor && !on)
+	{
+		CAS_LOG(("Stop cassette motor\n"));
+		st_cas->cycles_last = -1;
+	}
+	st_cas->motor = on;
+}
+
+
+static void *cassette_init(void)
+{
+	cassette_t *cas = malloc(sizeof(cassette_t));
+
+	memset(cas, 0, sizeof(cassette_t));
+	pzx_init(&cas->pzx);
+
+	st_cas = cas;
+	return cas;
+}
+
+
+static void cassette_close(void *p)
+{
+	cassette_t *cas = (cassette_t *)p;
+
+	pzx_close(&cas->pzx);
+
+	free(cas);
+}
+
+
+device_t cassette_device = 
+{
+	"Cassette",
+	0,
+	cassette_init,
+	cassette_close,
+	NULL,
+	NULL,
+	NULL,
+	NULL,
+	NULL
+};
+