Updated the style of the code in lib/string.c to conform to the rest of

the project.

Added the system call 'sys_panic' as well as the corresponding library
function panic() whose prototype is defined in unistd.h. This is to
allow userspace programs to deliberately crash the kernel for the
purpose of debugging.

Added the element 'write' as a function pointer in the tty_struct
structure. The purpose of this function pointer is to provide a means
for the TTY subsystem to notify the device driver of any newly added
data to the write queue.

Added the tty_write() function to the TTY subsystem. This function will
copy data provided by the user into the specified TTY device's write
queue, blocking if the queue's buffer is full. tty_write() will then
call the driver's write() function to notify it of new data.

Added the rsint_tx() function to the serial driver to handle transmit
interrupts by re-supplying the UART's transmit FIFO.

4 files changed, 132 insertions, 14 deletions

diff --git a/kernel/rs.s b/kernel/rs.s
index 9f3d4a6..69d31ae 100644
--- a/kernel/rs.s
+++ b/kernel/rs.s
@@ -1,7 +1,20 @@
 global rs_isr
-extern rs_handler
+extern rsint_rx
+extern rsint_tx
 extern rsputs
 
+%define RSBASE 0x3F8
+
+%define RSDATA    RSBASE
+%define RSINTEN   (RSBASE + 1)
+%define RSFIFOC   (RSBASE + 2)
+%define RSINTID   (RSBASE + 2)
+%define RSLINEC   (RSBASE + 3)
+%define RSMODEMC  (RSBASE + 4)
+%define RSLINES   (RSBASE + 5)
+%define RSMODEMS  (RSBASE + 6)
+%define RSSCRATCH (RSBASE + 7)
+
 rs_isr:
   pusha
   mov ax, ds
@@ -12,7 +25,24 @@ rs_isr:
   mov fs, ax
   mov gs, ax
 
-  call rs_handler
+  mov dx, RSINTID
+  in al, dx
+  test al, 1
+  jnz .skip
+  and al, 0x0E
+  cmp al, 0x04
+  je .rx
+  cmp al, 0x0C
+  je .rx
+  cmp al, 0x02
+  je .tx
+  jmp .skip
+.tx:
+  call rsint_tx
+  jmp .skip
+.rx:
+  call rsint_rx
+.skip:
   mov al, 0x20
   out 0x20, al
 
diff --git a/kernel/serial.c b/kernel/serial.c
index 39c5ee0..a133865 100644
--- a/kernel/serial.c
+++ b/kernel/serial.c
@@ -16,6 +16,7 @@
 #define RSDATA    RSBASE
 #define RSINTEN   (RSBASE + 1)
 #define RSFIFOC   (RSBASE + 2)
+#define RSINTID   (RSBASE + 2)
 #define RSLINEC   (RSBASE + 3)
 #define RSMODEMC  (RSBASE + 4)
 #define RSLINES   (RSBASE + 5)
@@ -27,8 +28,12 @@
 
 extern void rs_isr(void);
 
+/* internal function prototypes */
+void rsint_tx(void);
+
 struct tty_struct tty_rs = {
-  .init = &serial_init
+  .init = &serial_init,
+  .write = &rsint_tx
 };
 
 static char present;
@@ -70,11 +75,18 @@ void serial_init(void) {
   /* restore access to the divisor */
   outb(RSLINEC, inb(RSLINEC) & 0x7F);
   /* configure port parameters */
-  outb(RSFIFOC, 0x06);
+  outb(RSFIFOC, 0x07);
   outb(RSLINEC, 0x03);
   outb(RSMODEMC, 0x0B);
-  outb(RSINTEN, 0x01);
+  outb(RSINTEN, 0x03);
   inb(RSDATA);
+
+  /* test FIFO functionality */
+  if(inb(RSINTID) & 0xC0 != 0xC0) {
+    printk("[rs] Failed to enable FIFO on COM0!\n");
+    return;
+  }
+
   /* register the interrupt handler */
   register_isr(0x24, 0, &rs_isr);
   irq_enable(0x10);
@@ -85,7 +97,7 @@ void serial_init(void) {
   present = 1;
 }
 
-void rs_handler(void) {
+void rsint_rx(void) {
   struct tty_queue *q = &tty_rs.rqueue;
 
   if((inb(RSLINES) & 1) == 0)
@@ -98,3 +110,22 @@ void rs_handler(void) {
 
   wake_up(&q->waiting);
 }
+
+void rsint_tx(void) {
+  int copied = 0;
+  struct tty_queue *q = &tty_rs.wqueue;
+
+  while(q->pread != q->pwrite) {
+    /* we're done if the TX FIFO is full */
+    if((inb(RSLINES) & 0x20) == 0)
+      break;
+
+    outb(RSDATA, q->buf[q->pread]);
+    q->pread = (q->pread + 1) % TTY_BUF_SIZE;
+
+    copied = 1;
+  }
+
+  if(copied)
+    wake_up(&q->waiting);
+}
diff --git a/kernel/sys.c b/kernel/sys.c
index 6127f58..8e28edd 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1,5 +1,6 @@
 #include <errno.h>
 #include <kernel/con.h>
+#include <kernel/kernel.h>
 #include <kernel/sched.h>
 #include <kernel/serial.h>
 #include <kernel/tty.h>
@@ -84,6 +85,14 @@ ssize_t sys_read(void *buf, size_t len) {
   return tty_read(ctask->ctty, buf, len);
 }
 
+ssize_t sys_write(void *buf, size_t len) {
+  return tty_write(ctask->ctty, buf, len);
+}
+
+void sys_panic(void) {
+  panic();
+}
+
 int sys_dummy(void) {
   return -ENOSYS;
 }
diff --git a/kernel/tty.c b/kernel/tty.c
index 1946110..75c3701 100644
--- a/kernel/tty.c
+++ b/kernel/tty.c
@@ -16,11 +16,8 @@ static struct tty_struct *ttys[] = {
   &tty_rs
 };
 
-/* check if the buffer's empty and if so, go to sleep */
+/* check if a buffer's empty and if so, go to sleep */
 static int sleep_while_empty(struct tty_queue *q) {
-  if(q->pread != q->pwrite)
-    return 0;
-
   cli();
   while(1) {
     if(q->pread == q->pwrite)
@@ -37,6 +34,24 @@ static int sleep_while_empty(struct tty_queue *q) {
   }
 }
 
+/* check if a buffer's full and if so, go to sleep */
+static int sleep_while_full(struct tty_queue *q) {
+  cli();
+  while(1) {
+    if(q->pwrite == (q->pread - 1 % sizeof(q->buf)))
+      interruptible_sleep_on(&q->waiting);
+
+    /* check again to see if anything was removed, or we were interrupted */
+    if(q->pwrite == (q->pread - 1 % sizeof(q->buf))) {
+      sti();
+      return -1;
+    }
+
+    sti();
+    return 0;
+  }
+}
+
 ssize_t tty_read(unsigned tty, void *buf, size_t len) {
   size_t i;
   char *b = buf;
@@ -61,9 +76,45 @@ ssize_t tty_read(unsigned tty, void *buf, size_t len) {
     }
 
     *b++ = q->buf[q->pread];
-    q->pread = q->pread + 1 % TTY_BUF_SIZE;
+    q->pread = (q->pread + 1) % TTY_BUF_SIZE;
+  }
+
+  return len;
+}
+
+ssize_t tty_write(unsigned tty, void *buf, size_t len) {
+  size_t i;
+  char *b = buf;
+  struct tty_queue *q = &ttys[tty]->wqueue;
+
+  if(tty > NRTTY || ttys[tty] == NULL)
+    return -1;
+
+  if(len == 0)
+    return 0;
+
+  if(len > SSIZE_MAX)
+    len = SSIZE_MAX;
+
+  for(i = 0; i < len; i++) {
+    /* check if the buffer's full and if so, go to sleep */
+    if(sleep_while_full(q) < 0) {
+      if(i == 0)
+        return -EINTR;
+
+      return i;
+    }
+
+    q->buf[q->pwrite] = *b++;
+    q->pwrite = (q->pwrite + 1) % TTY_BUF_SIZE;
   }
 
+  /* tell the driver that new data is available */
+  cli();
+  if(ttys[tty]->write)
+    ttys[tty]->write();
+  sti();
+
   return len;
 }
 
@@ -77,9 +128,6 @@ void tty_init(void) {
     memset(&ttys[i]->rqueue, 0, sizeof(struct tty_queue));
     memset(&ttys[i]->wqueue, 0, sizeof(struct tty_queue));
 
-    ttys[i]->rqueue.pwrite = 1;
-    ttys[i]->wqueue.pwrite = 1;
-
     if(ttys[i]->init)
       ttys[i]->init();
   }