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

src/pzx.h

@@ -0,0 +1,71 @@
+/************************************************************************
+
+    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.
+
+*************************************************************************/
+
+typedef enum
+{
+	PZX_CLOSED,	/* File is not open */
+	PZX_IDLE,	/* File is open, no block loaded */
+	PZX_IN_PULS,	/* File is open, current block is a PULS block */
+	PZX_IN_DATA,	/* File is open, current block is a DATA block */
+	PZX_IN_PAUS,	/* File is open, current block is a PAUS block */
+} PZX_STATE;
+
+
+typedef struct pzxfile_t
+{
+	FILE *input;		/* Input PZX file */
+	uint8_t *curblock;	/* Currently-loaded block, if any */
+	int level;		/* Current signal level */
+	PZX_STATE state;	/* State machine current status */
+/* State variables for PULS */
+	uint32_t puls_ptr;	/* Pointer within PULS block */
+	uint32_t puls_len;	/* Length of PULS block */
+	uint32_t puls_count;	/* Count of pulses */
+	uint32_t puls_duration;	/* Duration of each pulse */
+	uint32_t puls_remain;	/* Time remaining in this pulse */
+/* State variables for PAUS */
+	uint32_t paus_remain;	/* Time remaining in this pause */
+/* State variables for DATA */
+	uint32_t data_ptr;	/* Pointer within DATA block */
+	uint32_t data_bits; 	/* Count of bits */
+	uint16_t data_tail;	/* Length of pulse after last bit */
+	uint8_t  data_mask;	/* Mask for current bit */
+	uint8_t	 data_p0;	/* Length of 0 encoding */	
+	uint8_t	 data_p1;	/* Length of 1 encoding */	
+	int	 data_p;	/* Current sequence being emitted */
+	uint32_t data_w;	/* Current waveform */
+	uint32_t data_remain;	/* Current data pulse time remaining */
+} pzxfile_t;
+
+uint8_t *pzx_load_block(FILE *fp);
+
+/* Initialise structure */
+void pzx_init(pzxfile_t *pzx);
+
+/* Open file for input */
+const char *pzx_open(pzxfile_t *pzx, FILE *fp);
+
+/* Close file */
+void pzx_close(pzxfile_t *pzx);
+
+/* Advance by 'time' samples (3.5MHz sample rate) and return current state */
+int pzx_advance(pzxfile_t *pzx, int time);