From 00660fb9143daf7fa04647bccd6047b9bf0f5e48 Mon Sep 17 00:00:00 2001
From: Christian Cunningham <cc@localhost>
Date: Fri, 21 Jan 2022 11:37:49 -0700
Subject: Scheduler Rewrite Start

---
 later/schedule.S | 195 +++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 140 insertions(+), 55 deletions(-)

(limited to 'later/schedule.S')

diff --git a/later/schedule.S b/later/schedule.S
index 1811c7c..a46654c 100644
--- a/later/schedule.S
+++ b/later/schedule.S
@@ -1,58 +1,143 @@
-.section .text
-.globl preserveregs
-preserveregs:
-	str r4,  [r0, #0x10]
-	str r5,  [r0, #0x14]
-	str r6,  [r0, #0x18]
-	str r7,  [r0, #0x1c]
-	str r8,  [r0, #0x20]
-	str r9,  [r0, #0x24]
-	str r10, [r0, #0x28]
-	str r11, [r0, #0x2c]
-	bx lr
-
-.globl restoreregs
-restoreregs:
-	ldr r4,  [r0, #0x10]
-	ldr r5,  [r0, #0x14]
-	ldr r6,  [r0, #0x18]
-	ldr r7,  [r0, #0x1c]
-	ldr r8,  [r0, #0x20]
-	ldr r9,  [r0, #0x24]
-	ldr r10, [r0, #0x28]
-	ldr r11, [r0, #0x2c]
-	bx lr
+.section ".text"
+.globl schedule
+// TODO: Implement Scheduler for IRQ
 
-.globl exetask
-exetask:
-	push {r0, r4, r5, r6, r7, r8, r9, r10, r11, lr}
-	// Restore registers from context switch
-	ldr r4,  [r0, #0x10]
-	ldr r5,  [r0, #0x14]
-	ldr r6,  [r0, #0x18]
-	ldr r7,  [r0, #0x1c]
-	ldr r8,  [r0, #0x20]
-	ldr r9,  [r0, #0x24]
-	ldr r10, [r0, #0x28]
-	ldr r11, [r0, #0x2c]
 
-	// Preserve system stack
-	ldr r1,  =msp
-	str sp, [r1]
-	// Setup task's stack
-	ldr sp, [r0, #0x34]
-	// Switch to task
-	ldr lr, [r0, #0x3c]
-	blx lr
-	// Restore system stack
-	ldr r1, =msp
-	ldr sp, [r1]
-	pop {r0, r4, r5, r6, r7, r8, r9, r10, r11, pc}
+// Save Context
+// reg = struct cpu_context*
+.macro save_context reg
+	str r4,  [\reg, #0x00]
+	str r5,  [\reg, #0x04]
+	str r6,  [\reg, #0x08]
+	str r7,  [\reg, #0x0c]
+	str r8,  [\reg, #0x10]
+	str r9,  [\reg, #0x14]
+	str r10, [\reg, #0x18]
+	str r11, [\reg, #0x1c]
+	str r12, [\reg, #0x20]
+	str lr,  [\reg, #0x24]
+.endm
+// Restore Context
+// reg = struct cpu_context*
+.macro restore_context reg
+	ldr r4, [\reg, #0x00]
+	ldr r5, [\reg, #0x04]
+	ldr r6, [\reg, #0x08]
+	ldr r7, [\reg, #0x0c]
+	ldr r8, [\reg, #0x10]
+	ldr r9, [\reg, #0x14]
+	ldr r10, [\reg, #0x18]
+	ldr r11, [\reg, #0x1c]
+	ldr r12, [\reg, #0x20]
+	ldr lr , [\reg, #0x24]
+.endm
 
-.section .data
-msp:
-	.space 4
-.section .data.stacks
-.globl stacks
-stacks:
-	.space 0x100000
+// Implemented the scheduler in Assembly since the C defined was messing around with the program stacks
+//  This way, I can be confident that the stacks will be unchanged
+schedule:
+	ldr r3, =scheduler
+	// Preserve context
+	ldr r0, [r3, #4]
+	// r0 = struct cpu_context*
+	save_context r0
+	// Get the next available thread
+	push {r1-r3, lr}
+	bl get_next_thread
+	pop {r1-r3, lr}
+	ldr r1,  [r3, #0] 
+	// r3 = struct Scheduler*
+	// r0 = struct LL* next_thread_ll
+	// r1 = struct LL* current_thread_ll
+	// Check if there is a valid currently running thread
+	cmp r1, #0
+	beq schedule.current_thread_nexists
+schedule.current_thread_exists:
+	cmp r0, r1
+	beq schedule.run_current
+	cmp r0, #0
+	moveq r0, r1 // Make the current running thread the next running thread if no next running thread
+	// Next is not the same as the current
+	// Preserve stack of current
+	ldr r2,  [r1, #0x8] // struct Thread* current
+	ldrh r1, [r2, #0x0e]
+	cmp r1, #2 // THREAD_WAITING
+	beq schedule.temp_status
+	cmp r1, #1 // THREAD_RUNNING
+	bne schedule.dont_modify_status
+schedule.temp_status:
+	mov r1, #0 // THREAD_READY
+	strh r1, [r2, #0x0e]
+schedule.dont_modify_status:
+	str sp,  [r2, #0x4] // void* stack // Preserve stack
+	// Preserve program counter of current
+	str lr,  [r2, #0x0] // void* thread // Preserve pc
+	ldr r2,  [r0, #0x8] // struct Thread* next
+	// Set new stack pointer
+	ldr sp,  [r2, #0x4]
+	// Set the thread as running
+	mov r1, #1 // THREAD_RUNNING
+	strh r1,  [r2, #0x0e] // unsigned short status
+	add r2,  r2, #0x18
+	// Set new running thread
+	str r0,  [r3, #0x0] // struct LL* next_thread_ll // Set new running thread
+	// Set new context
+	str r2,  [r3, #0x4] // struct cpu_context* ctx // Set new context
+	b schedule.run_current
+schedule.current_thread_nexists:
+	// r0 = struct LL* next_thread_ll
+	// r1 = 0 = struct LL* current_thread_ll
+	cmp r0, #0
+	beq schedule.no_next_thread
+	ldr r1, [r0, #0x8]
+	// r1 =  struct Thread* next_thread
+	// Store system stack pointer
+	ldr r2, =svcsp
+	push {r1}
+	ldr r1, [r2]
+	cmp r1, #0
+	pop {r1}
+	bne schedule.dont_overwrite_sys_stack
+	// Store if zero system stack
+	str sp, [r2]
+schedule.dont_overwrite_sys_stack:
+	// Move stack to next thread's stack pointer
+	ldr sp, [r1, #0x4] // void* stack
+	// Store the running thread ll entry
+	str r0, [r3, #0x0] // struct LL* rthread_ll
+	ldr r2, [r0, #0x8] // struct Thread* thread
+	mov r0, #1 // THREAD_RUNNING
+	strh r0, [r2, #0x0e]
+	// Set context
+	add r1, r1, #0x18 // struct cpu_context*
+	str r1, [r3, #0x4] // store to scheduler.ctx
+schedule.run_current:
+	// Restore context
+	ldr r2,  [r3, #0x4] // struct cpu_context* ctx // Set new context
+	restore_context r2
+	// Run
+	ldr r1, [r3, #0]
+	// r1 = struct LL* rthread_ll
+	ldr r1, [r1, #0x8]
+	// r1 = struct Thread* rthread
+	ldr r0, [r1, #0x0]
+	// r0 = void* thread
+	bx r0
+schedule.no_next_thread:
+	// r0 = 0 = struct LL* next_thread_ll
+	// r1 = 0 = struct LL* current_thread_ll
+	// No thread to run
+	// Restore sys context
+	ldr r0, =svccpu
+	str r0, [r3, #0x4] // Store context
+	ldr r0, =svcsp
+	ldr r1, [r0]
+	cmp r1, #0
+	beq schedule.exit
+	mov sp, r1 // Restore stack pointer
+	mov r1, #0
+	str r1, [r0] // Clear stack pointer
+schedule.exit:
+	// Restore register context
+	ldr r2,  [r3, #0x4] // struct cpu_context* ctx // Set new context
+	restore_context r2
+	bx lr
-- 
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