Implement schedsleep() syscall to sleep a process for a given time

kernel/hal/x86_64/intr.c

@@ -193,9 +193,7 @@ void hal_syscalldispatch(IntrStackFrame *frame) {
       frame->regs.rax = E_BADSYSCALL;
       return;
     }
-    spinlock_acquire(&PROCS.spinlock);
     uint64_t calling_proc_pid = PROCS.current->pid;
-    spinlock_release(&PROCS.spinlock);
     hal_intr_enable();
     int32_t ret = fn(frame, calling_proc_pid, frame->regs.rdi, frame->regs.rsi, frame->regs.rdx,
                                               frame->regs.r10, frame->regs.r8,  frame->regs.r9);

kernel/hal/x86_64/pit.c

@@ -29,12 +29,11 @@ void pit_init(void) {
   uint32_t hz = 1000;
   uint32_t div = PIT_FREQ / hz;
   io_out8(PIT_CMD, PIT_CMD_BINARY | PIT_CMD_MODE3 | PIT_CMD_RW_BOTH | PIT_CMD_COUNTER0);
-  io_out8(PIT_COUNTER0, div);
+  io_out8(PIT_COUNTER0, div & 0xFF);
   io_out8(PIT_COUNTER0, div >> 8);
 }
 
 void pit_wait(uint32_t ms) {
   uint32_t now = PIT_TICKS;
-  ++ms;
   while (PIT_TICKS - now < ms);
 }

kernel/syscall/sched.c

@@ -9,3 +9,9 @@
 int32_t SYSCALL0(sys_schedrelease) {
   return E_DOSCHEDULING;
 }
+
+int32_t SYSCALL1(sys_schedsleep, ms1) {
+  uint32_t ms = (uint32_t)ms1;
+  hal_wait(ms);
+  return E_OK;
+}

kernel/syscall/sched.h

@@ -5,5 +5,6 @@
 #include "syscall.h"
 
 int32_t SYSCALL0(sys_schedrelease);
+int32_t SYSCALL1(sys_schedsleep, ms1);
 
 #endif // SYSCALL_SCHED_H_

kernel/syscall/syscall.c

@@ -27,6 +27,7 @@ SyscallFn SYSCALL_TABLE[SYSCALLS_MAX] = {
   [SYS_MMAN_UNMAP] = &sys_mman_unmap,
 
   [SYS_SCHEDRELEASE] = &sys_schedrelease,
+  [SYS_SCHEDSLEEP]   = &sys_schedsleep,
 
   [SYS_RAND]       = &sys_rand,