4 files changed, 42 insertions, 15 deletions

diff --git a/kernel/boot.s b/kernel/boot.s
index db846c9..d609611 100644
--- a/kernel/boot.s
+++ b/kernel/boot.s
@@ -2,6 +2,7 @@ global gdt
 global idt
 global kboot
 global register_isr
+global register_trap
 extern con_init
 extern hd_init
 extern kmain
@@ -191,8 +192,27 @@ register_isr:
   mov eax, [ebp+12]
   and al, 3
   shl al, 5
-  mov cl, [edx+5]
-  and cl, 0x9F
+  mov cl, 0x8E
+  or cl, al
+  mov [edx+5], cl
+  pop ebp
+  ret
+
+; void register_trap(uint8_t n, uint8_t dpl, void *handler);
+register_trap:
+  push ebp
+  mov ebp, esp
+  mov edx, [ebp+8]
+  shl edx, 3
+  add edx, idt
+  mov eax, [ebp+16]
+  mov [edx], ax
+  shr eax, 16
+  mov [edx+6], ax
+  mov eax, [ebp+12]
+  and al, 3
+  shl al, 5
+  mov cl, 0x8F
   or cl, al
   mov [edx+5], cl
   pop ebp
diff --git a/kernel/sys.c b/kernel/sys.c
index 86fae41..20494de 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -7,13 +7,7 @@
 #include <time.h>
 #include <unistd.h>
 
-extern uint32_t ticks;
-
 int sys_puts(char *s) {
-  uint32_t sigs = 5;
-  printk("[kernel] Setting signals %01x for PID 0x%04x\n", sigs, ctask->pid);
-  ctask->signal |= sigs;
-
   printk("[%04x] ", ctask->pid);
   return printk(s);
 }
diff --git a/kernel/timer.s b/kernel/timer.s
index c3af34b..b96e1f1 100644
--- a/kernel/timer.s
+++ b/kernel/timer.s
@@ -1,9 +1,11 @@
+global ticked
 global ticks
 global timer_init
 extern check_signals
 extern register_isr
 extern sched_tick
 
+ticked: dd 0
 ticks: dd 0
 
 tick_handler:
@@ -17,17 +19,20 @@ tick_handler:
   mov es, ax
   mov fs, ax
   mov gs, ax
-
   ; handle the timer tick
+  mov dword [ticked], 1
   inc dword [ticks]
   mov al, 0x20
   out 0x20, al
-
-  ; call the scheduler
+  ; check that the user isn't executing in kernel space
+  mov eax, [esp+38]
+  test eax, 0x03
+  jz .end
+  ; if it isn't, call the scheduler
   call sched_tick
   ; handle any pending signals before returning to normal execution
   call check_signals
-
+.end:
   ; restore the data segment selectors
   pop ax
   mov ds, ax
diff --git a/kernel/traps.s b/kernel/traps.s
index 73e7f64..36b3423 100644
--- a/kernel/traps.s
+++ b/kernel/traps.s
@@ -11,8 +11,10 @@ extern ctask
 extern idt
 extern panic
 extern printk
-extern register_isr
+extern register_trap
+extern reschedule
 extern sighandler_default
+extern ticked
 
 ; here we define offsets into task_struct.
 ; if task_struct is modified, this must be
@@ -269,6 +271,7 @@ exc_reserved:
 syscall_handler:
   SAVE
 
+  mov dword [ticked], 0
   ; push the arguments onto the stack, then
   ; calculate the offset for the appropriate
   ; handler function and call it
@@ -282,8 +285,13 @@ syscall_handler:
   add esp, 12
   ; preserve the syscall's return value
   mov [esp+30], eax
-  mov eax, esp
+  ; check if the timer fired while we were in kernel mode
+  mov eax, [ticked]
+  jz .skip
+  call reschedule
+.skip:
   ; check pending signals and handle them (if any)
+  mov eax, esp
   push eax
   call check_signals
   add esp, 4
@@ -379,7 +387,7 @@ syscall_init:
   push syscall_handler
   push dword 3
   push dword 0x80
-  call register_isr
+  call register_trap
   add esp, 12
   pop ebp
   ret