From ed7b9318bc9ac285250b117f87f47fe7f84af51b Mon Sep 17 00:00:00 2001
From: Christian Cunningham <cc@localhost>
Date: Fri, 21 Jan 2022 12:55:57 -0700
Subject: Added scheduling logic

---
 src/sys/schedule.S | 47 +++++++++++++++++++++++++++++++++++------------
 src/sys/schedule.c |  2 ++
 2 files changed, 37 insertions(+), 12 deletions(-)

(limited to 'src/sys')

diff --git a/src/sys/schedule.S b/src/sys/schedule.S
index 298646a..4913034 100644
--- a/src/sys/schedule.S
+++ b/src/sys/schedule.S
@@ -1,26 +1,49 @@
 .section ".text"
 .globl schedule
-
-// Implicit: SVC Mode
 .macro preserve_ctx
 	cps #0x1f // Sys mode
-	push {r0-r12, lr} // Restore usr regs
-	cps #0x10 // Svc mode
+	// Store Usr regs
+	stmfd sp!, {r0-r12}
+	stmfd sp!, {lr}
 	ldr r3, =scheduler // struct Scheduler
-	ldr r3, [r3, #4] // struct Thread* rthread
-	str lr, [r3, #0] // svc_lr -> void* pc
+	ldr r2, [r3, #0] // struct Thread* rthread
+	str lr, [r2, #0] // svc_lr -> void* pc
+	str sp, [r2, #4] // svc_lr -> void* sp
+	cps #0x10 // Svc mode
 .endm
 
 .macro restore_ctx
 	ldr r3, =scheduler // struct Scheduler
-	ldr r3, [r3, #4] // struct Thread* rthread
-	ldr lr, [r3, #0] // void* pc -> lr_svc
+	ldr r2, [r3, #0] // struct Thread* rthread
+	ldr lr, [r2, #0] // void* pc -> lr_svc
+	ldr r0, [r2, #4] // void* sp -> r0
 	cps #0x1f // Sys mode
-	pop {r0-r12,lr} // Restore usr regs
+	mov sp, r0 // Set stack pointer
+	// Restore Usr regs
+	ldmfd sp!, {lr}
+	ldmfd sp!, {r0-r12}
 	cps #0x10 // Svc mode
 .endm
 
+// Assumption: Enter in SVC mode
 schedule:
-	//preserve_ctx
-	//restore_ctx
-	//bx lr
+	preserve_ctx
+	ldr r1, =irqlr
+	ldr r0, [r1]
+	cmp r0, #0
+	beq 1f
+	// Replace LR with IRQ's LR
+	mov lr, r0
+	// Clear IRQ's LR
+	mov r0, #0
+	str r0, [r1]
+1:
+	// bl get_next_thread // next_thread -> r0
+	ldr r3, =scheduler
+	ldr r2, [r3, #0] // struct Thread* current
+	cmp r0, r2 // current = next?
+	beq 2f
+	str r0, [r3, #0] // next -> rthread
+2:
+	restore_ctx
+	movs pc, lr
diff --git a/src/sys/schedule.c b/src/sys/schedule.c
index 96dc678..0dc89e9 100644
--- a/src/sys/schedule.c
+++ b/src/sys/schedule.c
@@ -1,3 +1,5 @@
 void init_scheduler(void)
 {
+	// Set rthread to usrloopthread - an infinitely running thread so that the pointer will never be null
+	// Initialize Rotating Buffers
 }
-- 
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