From 59cac783f5ba12a47308b05b87d5cfa769473a49 Mon Sep 17 00:00:00 2001
From: Jake Mannens <jake72360@gmail.com>
Date: Wed, 11 Jul 2018 05:38:01 +1000
Subject: Modified the tick_handler interrupt routine in timer.s so that it no
 longer calls reschedule() directly. It now calls sched_tick() so that the
 scheduler can make it's own decisions relating to handling the timer
 interrupt.

The reschedule() function now *actually* implements a basic round-robin
scheduling algorithm that iterates through the list of tasks. This is
still a temporary algorithm but at least it now includes *all* runnable
processes instead of switching back and forth between process 1 and 2.
---
 kernel/asm.s   |  5 ++++-
 kernel/sched.c | 18 ++++++++++++++----
 kernel/timer.s |  4 ++--
 3 files changed, 20 insertions(+), 7 deletions(-)

(limited to 'kernel')

diff --git a/kernel/asm.s b/kernel/asm.s
index 0bf9067..6d35334 100644
--- a/kernel/asm.s
+++ b/kernel/asm.s
@@ -3,6 +3,7 @@ global switch_to
 global set_tss
 extern cstate
 extern ctask
+extern ctaskn
 extern gdt
 extern save_state
 
@@ -27,9 +28,11 @@ switch_to:
   ltr ax
   ; copy the saved state into the previous TSS
   call save_state
-  ; update ctask
+  ; update ctask and ctaskn
   mov ebx, [ebp+12]
   mov [ctask], ebx
+  mov ebx, [ebp+8]
+  mov [ctaskn], ebx
   ; calculate the task segment index and jump to it
   mov ebx, [ebp+8]
   add ebx, 5
diff --git a/kernel/sched.c b/kernel/sched.c
index dd75d47..8469005 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -48,6 +48,7 @@ struct task_state {
 } __attribute__((packed));
 
 struct task_struct *ctask;
+uint32_t ctaskn;
 struct task_state *cstate;
 
 static struct task_struct tasks[NRTASKS];
@@ -192,6 +193,7 @@ void sched_init(void) {
   ctask = NULL;
   cstate = NULL;
 
+  create_proc(&_usrbin_start, (size_t) &_usrbin_size);
   create_proc(&_usrbin_start, (size_t) &_usrbin_size);
   create_proc(&_usrbin_start, (size_t) &_usrbin_size);
 
@@ -221,12 +223,20 @@ void save_state(void) {
 }
 
 void reschedule(void) {
+  int i;
+  uint32_t n;
+
   if(ctask == NULL)
     return;
 
-  if(ctask == &tasks[0]) {
-    switch_to(1, &tasks[1]);
-  } else {
-    switch_to(0, &tasks[0]);
+  n = ctaskn;
+  for(i = 0; i < NRTASKS; i++) {
+    n = (n + 1) % NRTASKS;
+    if(tasks[n].pid)
+      switch_to(n, &tasks[n]);
   }
 }
+
+void sched_tick(void) {
+  reschedule();
+}
diff --git a/kernel/timer.s b/kernel/timer.s
index c84a847..12ea9d0 100644
--- a/kernel/timer.s
+++ b/kernel/timer.s
@@ -2,7 +2,7 @@ global ticks
 global timer_init
 extern cstate
 extern register_isr
-extern reschedule
+extern sched_tick
 
 ticks: dd 0
 
@@ -26,7 +26,7 @@ tick_handler:
   out 0x20, al
 
   ; call the scheduler
-  call reschedule
+  call sched_tick
 
   ; restore the data segment selectors
   pop ax
-- 
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