Defined ssize_t in unistd.h.

Added the _syscall2 macro to unistd.h to facilitate system calls that
require two arguments to be passed.

Modified the ATA driver to simply abort initialisation if a drive is not
found, or cannot be configured. This will allow the kernel to function
on a diskless system without invoking panic() unnecessarily.

Added the functions irq_enable() and irq_disable() to asm/interrupt.h to
make it easier for C code to mask and unmask IRQ's on each PIC.

Moved the declaration for rsputs() from kernel/con.h to the new
kernel/serial.h file since this is a function provided by the serial
driver.

Implemented a basic I/O input framework. This involves the new system
call sys_read, which takes an I/O read request and directs it to the
appropriate kernel handler function depending on the calling process'
ctty value. This mechanism is identical to the sys_puts system call.

Added the rsread() function to service sys_read calls from processes
whose ctty value is equal to 1. This function will continually copy data
from the serial buffer to the location specified. If there is not a
sufficient amount of new data in the buffer to satisfy the request, the
process is put into the TSTATE_UNINTERRUPTIBLE state and the scheduler
is called to switch tasks. Prior to calling the scheduler, the function
will set the waiting_task pointer to the calling process. This pointer
will later be used by the interrupt handler to wake the process when new
data arrives.

Added an interrupt handler to service the IRQ4 (UART) interrupt. This
subroutine is a stub which will save the machine's state then transfer
control to rs_handler() in serial.c which will read bytes from the
serial port and place them in a buffer. Before returning, rs_handler()
checks the waiting_task pointer to see if a task is waiting for the
newly received data and if so, it sets the task's state to
TSTATE_RUNNING before resetting the pointer to NULL and returning.
Ideally, the scheduler should be invoked at this point to select another
task but since our basic round-robin scheduler currently has no concept
of task priorities (and for the sake of simplicity), we will avoid
invoking the scheduler in response to interrupts for now.

5 files changed, 101 insertions, 7 deletions

diff --git a/kernel/hd.c b/kernel/hd.c
index 706d503..65ebfd7 100644
--- a/kernel/hd.c
+++ b/kernel/hd.c
@@ -27,13 +27,13 @@ void hd_init(void) {
     s = inb(0x1F7);
     if(!s) {
       printk("[hd] Master drive not detected on primary bus!\n");
-      panic();
+      return;
     }
     if(s & ST_ERR) {
       if(!inb(0x1F4) && !inb(0x1F5))
         continue;
       printk("[hd] IDENTIFY command error!\n");
-      panic();
+      return;
     }
     if(s & ST_DRQ && !(s & ST_ERR))
       break;
diff --git a/kernel/rs.s b/kernel/rs.s
new file mode 100644
index 0000000..9f3d4a6
--- /dev/null
+++ b/kernel/rs.s
@@ -0,0 +1,25 @@
+global rs_isr
+extern rs_handler
+extern rsputs
+
+rs_isr:
+  pusha
+  mov ax, ds
+  push ax
+  mov ax, 0x10
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+
+  call rs_handler
+  mov al, 0x20
+  out 0x20, al
+
+  pop ax
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+  popa
+  iret
diff --git a/kernel/serial.c b/kernel/serial.c
index 86bbd87..d96359b 100644
--- a/kernel/serial.c
+++ b/kernel/serial.c
@@ -1,5 +1,9 @@
+#include <asm/interrupt.h>
 #include <asm/io.h>
 #include <kernel/con.h>
+#include <kernel/sched.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 /* 115200 baud */
 #define DIVISOR 1
@@ -18,10 +22,16 @@
 #define rswait()\
   while((inb(RSLINES) & 0x20) == 0);
 
+extern void rs_isr(void);
+
+static char rxbuf[256];
+static unsigned rxread, rxwrite;
+static struct task_struct *waiting_task;
+
 int rsputs(char *s) {
   while(*s) {
     rswait();
-    if(*s == '\n') {
+    if(*s == '\n' || *s == '\r') {
       outb(RSDATA, '\n');
       rswait();
       outb(RSDATA, '\r');
@@ -50,9 +60,55 @@ void serial_init(void) {
   /* restore access to the divisor */
   outb(RSLINEC, inb(RSLINEC) & 0x7F);
   /* configure port parameters */
+  outb(RSFIFOC, 0x06);
   outb(RSLINEC, 0x03);
-  outb(RSINTEN, 0x00);
+  outb(RSMODEMC, 0x0B);
+  outb(RSINTEN, 0x01);
+  inb(RSDATA);
+  /* register the interrupt handler */
+  register_isr(0x24, 0, &rs_isr);
+  irq_enable(0x10);
 
   rsputs("[kernel] Serial monitor initialized!\n\r");
   printk("[rs] Serial port COM0 initialized!\n");
+
+  rxread = 0;
+  rxwrite = 1;
+  waiting_task = NULL;
+}
+
+ssize_t rsread(void *buf, size_t len) {
+  ssize_t n = len;
+  char *b = buf;
+
+  if(len == 0)
+    return 0;
+
+  while(n--) {
+    if(rxread == rxwrite) {
+      /* put the current task to sleep */
+      waiting_task = ctask;
+      ctask->state = TSTATE_UNINTERRUPTIBLE;
+      reschedule();
+    }
+
+    *b++ = rxbuf[rxread];
+    rxread = rxread + 1 % sizeof(rxbuf);
+  }
+
+  return len;
+}
+
+void rs_handler(void) {
+  if((inb(RSLINES) & 1) == 0)
+    return;
+  if(rxwrite == (rxread - 1 % sizeof(rxbuf)))
+    return;
+  rxbuf[rxwrite] = inb(RSDATA);
+  rxwrite = rxwrite + 1 % sizeof(rxbuf);
+
+  if(waiting_task != NULL) {
+    waiting_task->state = TSTATE_RUNNING;
+    waiting_task = NULL;
+  }
 }
diff --git a/kernel/sys.c b/kernel/sys.c
index 986c4dd..cfe9483 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1,6 +1,7 @@
 #include <errno.h>
 #include <kernel/con.h>
 #include <kernel/sched.h>
+#include <kernel/serial.h>
 #include <signal.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -10,14 +11,15 @@
 
 int sys_puts(char *s) {
   char buf[8];
-  sprintf(buf, "[%04x] ", ctask->pid);
 
   if(ctask->ctty < 0)
     return EOF;
 
+  sprintf(buf, "[%04x] ", ctask->pid);
+
   switch(ctask->ctty) {
     case 1:
-      rsputs(buf);
+      /* rsputs(buf); */
       return rsputs(s);
       break;
     default:
@@ -77,6 +79,17 @@ int sys_ctty(int ctty) {
   return 0;
 }
 
+ssize_t sys_read(void *buf, size_t len) {
+  switch(ctask->ctty) {
+    case 1:
+      return rsread(buf, len);
+      break;
+    default:
+      return -EBADF;
+      break;
+  }
+}
+
 int sys_dummy(void) {
   return -ENOSYS;
 }
diff --git a/kernel/timer.s b/kernel/timer.s
index 6d95281..e6da428 100644
--- a/kernel/timer.s
+++ b/kernel/timer.s
@@ -55,7 +55,7 @@ timer_init:
   push dword 0x20
   call register_isr
   add esp, 12
-  ; initialize the pit
+  ; initialize the PIT
   mov ax, 0x36
   out 0x43, al
   mov ax, 0x2E9C ; 10ms tick interval