Removes wfi() from scheduler when waiting on process start.

kernel/src/sched.c

@@ -123,9 +123,9 @@ void sched(proc_t *p)
 		p = sched_fetch(hartid, &start_time, &end_time);
 	} while (!p);
 
-	timeout_set(hartid, start_time);
-	while (!(csrr_mip() & MIP_MTIP))
-		wfi();
 	timeout_set(hartid, end_time);
+	while (time_get() < start_time)
+		;
+
 	trap_exit(p);
 }

kernel/src/trap.S

@@ -16,7 +16,7 @@
 trap_entry:
 	/* Save user tp to scratch, load PCB pointer */
 	csrrw	a0,mscratch,a0
-	beqz	a0,__hang
+	beqz	a0,_machine_yield
 
 	sd	ra,PROC_RA(a0)
 	sd	sp,PROC_SP(a0)
@@ -79,14 +79,19 @@ _syscall:
 	csrw	mstatus,x0
 	tail	handle_syscall
 
+_machine_yield:
+	csrrw	a0,mscratch,a0
+	ld_sp	t0
+	csrr	t0,mcause
+
 _yield:
-	li t1,(7 | 1 << 63)
-	bne t0,t1,__hang
+	li	t1,0x8000000000000007
+	bne	t0,t1,__hang
 	/* Call scheduler */
 	tail	sched
 
 trap_exit:
-
+	csrw	mstatus,MSTATUS_MIE
 	/* Load PMP registers */
 	ld	s0,PROC_PMPADDR0(a0)
 	ld	s1,PROC_PMPADDR1(a0)
@@ -108,6 +113,7 @@ trap_exit:
 	csrw	pmpcfg0,s8
 	beqz	s8,trap_exit
 trap_resume:
+	csrw	mstatus,MSTATUS_MIE
 
 	/* Load call-used registers, ra, sp, gp, tp, pc */
 	ld	t0,PROC_PC(a0)