From 2b30f30a330ee9bc9feb9ec4e55c8b6f3e6eb8fe Mon Sep 17 00:00:00 2001
From: Ben Burwell <ben@benburwell.com>
Date: Wed, 1 Apr 2015 20:29:53 -0400
Subject: as of 2013-11-18

---
 com.c | 259 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 259 insertions(+)
 create mode 100644 com.c

(limited to 'com.c')

diff --git a/com.c b/com.c
new file mode 100644
index 0000000..5ddba08
--- /dev/null
+++ b/com.c
@@ -0,0 +1,259 @@
+/**
+ * MPX OS
+ * CSI350 Operating Systems
+ * Fall 2013
+ * Averill Morash, Ben Burwell
+ * COM.C
+ */
+
+#include <dos.h>
+#include <stdio.h>
+#include <string.h>
+#include "mpx.h";
+
+
+void interrupt (*vect0c)();
+dcb com;
+
+int com_opened;
+
+int com_open(int * flag, int rate) {
+  unsigned char imr;
+  unsigned char mcr;
+  unsigned char ier;
+  unsigned char lcr;
+
+  disable();
+
+  if (com_opened == NULL || com_opened == 0) {
+	com_opened = 1;
+  } else {
+	return -2;
+  }
+
+  // modify the interrupt vector table
+  vect0c = getvect(0x0c);
+  setvect(0x0c, &com_int);
+
+  // set baud rate
+  // first we need to set bit 7 of LCR
+  // to be 1 so that we can set the baud
+  // rate divisor.
+  lcr = inportb(LCR);
+  lcr = lcr | 0x80;
+  outportb(LCR, lcr);
+
+  // Now we can access the divisor.
+  // Clock rate is 1.8432 MHz. We want
+  // 1200 bps/baud.
+  // 1843200 / (1200 * 16) = 96 = 0x0060
+  // So the MSB is 0x00 and the LSB is 0x60
+
+  if (rate != 1200) {
+	return -3;
+  }
+
+  outport(BRDR_MSB, 0x00);
+  outportb(BRDR_LSB, 0x60);
+
+  // Now set the LCR
+  lcr = inportb(LCR);
+
+  // b7, b3, b2 = 0
+  lcr = lcr & 0x73;
+
+  // b0, b1 = 1
+  lcr = lcr | 0x03;
+
+  outportb(LCR, lcr);
+
+  // set IMR to allow COM interrupts
+  // set b4 = 0
+  imr = inportb(IMR);
+  imr = imr & 0xef;
+  outportb(IMR, imr);
+
+  // set MCR to enable interrupts from
+  // the UART
+  // on MCR, b3 = 1
+  mcr = inportb(MCR);
+  mcr = mcr | 0x08;
+  outportb(MCR, mcr);
+
+  // use IER to indicate which serial
+  // interrupts are enabled
+  // b0 = 1, b1 = 0
+  ier = inportb(IER);
+  ier = ier | 0x01;
+  ier = ier & 0xfd;
+  outportb(IER, ier);
+
+  // set up the DCB
+  com.event_flag = flag;
+  dcb_init(&com);
+
+  // enable interrupts
+  enable();
+
+  return 0;
+}
+
+void com_close() {
+  disable();
+  setvect(0x0c, vect0c);
+  enable();
+}
+
+void interrupt com_int() {
+  int iir;
+  int ret = 0; //0 indicates not finished, 1 indicated finshed
+
+  // check IIR to see what caused the interrupt
+  iir = inportb(IIR);
+  // only look at bits 1, 2
+  iir = iir & 0x06; // 0000-0110
+
+  if (iir == 0x02) { // 0000-0010
+	ret = com_write_int();
+  } else if (iir == 0x04) { // 0000-0100
+	ret = com_read_int();
+  } else {
+	// something is wrong
+	return;
+  }
+
+  if (ret == 1) {
+	IO_complete();
+  }
+
+  // write end of interrupt to 8259
+  outportb(0x20, 0x20);
+
+  return;
+
+}
+
+int com_read(char far * buffer, int far * length) {
+
+  char dq;
+  int i;
+
+  if (&com == NULL) {
+	// com not yet open
+	return -1;
+  }
+
+  // check for invalid length
+  if (*length < 1) {
+	return -3;
+  }
+
+  // check if DCB is free
+  if (com.current_op != NO_OP) {
+	// previous IO not yet complete
+	// TODO: we should block this process
+	return -2;
+  }
+
+  com.buffer = buffer;
+  com.length = length;
+  com.current_op = READ_OP;
+  com.count = 0;
+
+  strcpy(buffer, "");
+
+  i = 0;
+
+  while (com.ring_count > 0 && strlen(buffer) < *length) {
+
+	dq = dcb_dequeue(&com);
+	//strcat(buffer, &dq);
+	buffer[i] = dq;
+	i++;
+  }
+
+  buffer[i] = '\0';
+  com.count = i;
+
+  return 0;
+}
+
+int com_write(char far * buffer, int far * length) {
+  int ier;
+
+  // check that com has been initialized
+  if (&com == NULL) {
+	return -1;
+  }
+
+  // check that com is not busy
+  if (com.current_op != NO_OP) {
+	return -2;
+  }
+
+  // check that the length is valid
+  if (*length < 1) {
+	return -3;
+  }
+
+  // initialize DCB
+  com.buffer = buffer;
+  com.length = length;
+  com.current_op = WRITE_OP;
+  com.count = 0;
+
+  // enable THR interrupts
+  ier = inportb(IER);
+  // bit 1 should be 1
+  ier = ier | 0x02;
+  outportb(IER, ier);
+
+  return 0;
+}
+
+int com_read_int() {
+  char rbr;
+
+  rbr = inportb(RBR);
+
+  if (com.current_op == READ_OP && com.count < *(com.length)) {
+	  if (rbr == 0x0d || com.count == (*(com.length) - 1)) {
+		com.buffer[com.count] = '\0';
+		com.count++;
+		*com.length = com.count;
+		com.current_op = NO_OP;
+		*(com.event_flag) = 1;
+		return 1;
+	  } else {
+		com.buffer[com.count] = rbr;
+		com.count++;
+	  }
+  } else {
+	dcb_enqueue(&com, rbr);
+  }
+
+  return 0;
+}
+
+int com_write_int() {
+  int ier;
+
+  // if there are more characters to write
+  if (*(com.length) > com.count) {
+	// write a character
+	outportb(THR, com.buffer[com.count]);
+	com.count++;
+	return 0;
+  } else {
+	// no chars to write
+	// disable THR interrupts
+	ier = inportb(IER);
+	ier = ier & 0xfd;
+	outportb(IER, ier);
+
+	// set event flag
+	com.current_op = NO_OP;
+	*(com.event_flag) = 1;
+	return 1;
+  }
+}
-- 
cgit v1.2.3