diff options
Diffstat (limited to 'com.c')
| -rw-r--r-- | com.c | 55 |
1 files changed, 47 insertions, 8 deletions
@@ -3,7 +3,8 @@ * CSI350 Operating Systems
* Fall 2013
* Averill Morash, Ben Burwell
- * COM.C
+ *
+ * File: com.c
*/
#include <dos.h>
@@ -16,6 +17,7 @@ void interrupt (*vect0c)(); int com_opened;
+// Open the com port
int com_open(int * flag, int rate) {
unsigned char imr;
unsigned char mcr;
@@ -24,13 +26,15 @@ int com_open(int * flag, int rate) { disable();
+ // Ensure com has not already been opened, if
+ // it has, we must return.
if (com_opened == NULL || com_opened == 0) {
com_opened = 1;
} else {
return -2;
}
- // modify the interrupt vector table
+ // Modify the interrupt vector table
vect0c = getvect(0x0c);
setvect(0x0c, &com_int);
@@ -48,6 +52,7 @@ int com_open(int * flag, int rate) { // 1843200 / (1200 * 16) = 96 = 0x0060
// So the MSB is 0x00 and the LSB is 0x60
+ // Ensure baud rate is valid
if (rate != 1200) {
return -3;
}
@@ -97,17 +102,27 @@ int com_open(int * flag, int rate) { return 0;
}
+// Com Close
void com_close() {
disable();
+
+ // restore MS-DOS com vector
setvect(0x0c, vect0c);
+
enable();
}
+// Interrupt handler
void interrupt com_int() {
int iir;
int *lst_stk;
- int ret = 0; //0 indicates not finished, 1 indicated finshed
+ // 0 indicates not finished, 1 indicated finshed
+ int ret = 0;
+
+ disable();
+
+ // save base pointer
lst_stk = _BP;
// check IIR to see what caused the interrupt
@@ -120,10 +135,11 @@ void interrupt com_int() { } else if (iir == 0x04) { // 0000-0100
ret = com_read_int();
} else {
- // something is wrong
+ // interrupt was not read or write
return;
}
+ // if the operation is done, call IO_complete
if (ret == 1) {
IO_complete(COM, lst_stk);
}
@@ -131,70 +147,92 @@ void interrupt com_int() { // write end of interrupt to 8259
outportb(0x20, 0x20);
+ enable();
return;
}
+// Read from the com port
int com_read(char far * buffer, int far * length) {
char dq;
int i;
+ disable();
+
+ // if we haven't yet opened com, we can't proceed
if (&com == NULL) {
- // com not yet open
+ enable();
return -1;
}
// check for invalid length
if (*length < 1) {
+ enable();
return -3;
}
// check if DCB is free
if (com.current_op != NO_OP) {
// previous IO not yet complete
- // TODO: we should block this process
+ enable();
return -2;
}
+ if (buffer == NULL || length == NULL) {
+ printf("error in com_read\n");
+ enable();
+ return;
+ }
+ // set up the DCB
com.buffer = buffer;
com.length = length;
com.current_op = READ_OP;
com.count = 0;
+ // clear the buffer
strcpy(buffer, "");
+ // now we need to use the ring buffer to place typed-ahead
+ // characters into the buffer
+
+ // keep track of how many characters are copied from the
+ // ring buffer.
i = 0;
while (com.ring_count > 0 && strlen(buffer) < *length) {
-
dq = dcb_dequeue(&com);
- //strcat(buffer, &dq);
buffer[i] = dq;
i++;
}
+ // place a null character at the end of the buffer
buffer[i] = '\0';
com.count = i;
+ enable();
return 0;
}
int com_write(char far * buffer, int far * length) {
int ier;
+ disable();
// check that com has been initialized
if (&com == NULL) {
+ enable();
return -1;
}
// check that com is not busy
if (com.current_op != NO_OP) {
+ enable();
return -2;
}
// check that the length is valid
if (*length < 1) {
+ enable();
return -3;
}
@@ -210,6 +248,7 @@ int com_write(char far * buffer, int far * length) { ier = ier | 0x02;
outportb(IER, ier);
+ enable();
return 0;
}
|