Remove the idle process.

[bertos.git] / bertos / kern / proc.c

diff --git a/bertos/kern/proc.c b/bertos/kern/proc.c
index c422e729c6912963f51bfcd89f75a7cee269e290..623c1d3fb5d87dba4ceb91b5c35ddcd6f85749c8 100644 (file)
--- a/bertos/kern/proc.c
+++ b/bertos/kern/proc.c
@@ -62,6 +62,14 @@
 
 #define PROC_SIZE_WORDS (ROUND_UP2(sizeof(Process), sizeof(cpu_stack_t)) / sizeof(cpu_stack_t))
 
+/**
+ * CPU dependent context switching routines.
+ *
+ * Saving and restoring the context on the stack is done by a CPU-dependent
+ * support routine which usually needs to be written in assembly.
+ */
+EXTERN_C void asm_switch_context(cpu_stack_t **new_sp, cpu_stack_t **save_sp);
+
 /*
  * The scheduer tracks ready processes by enqueuing them in the
  * ready list.
@@ -139,8 +147,6 @@ void proc_init(void)
        monitor_init();
        monitor_add(current_process, "main");
 #endif
-       proc_schedInit();
-
        MOD_INIT(proc);
 }
 
@@ -430,3 +436,56 @@ iptr_t proc_currentUserData(void)
 {
        return current_process->user_data;
 }
+
+/**
+ * Call the scheduler and eventually replace the current running process.
+ */
+void proc_schedule(void)
+{
+       Process *old_process = current_process;
+
+       IRQ_ASSERT_DISABLED();
+
+       /* Poll on the ready queue for the first ready process */
+       LIST_ASSERT_VALID(&proc_ready_list);
+       while (!(current_process = (struct Process *)list_remHead(&proc_ready_list)))
+       {
+               /*
+                * Make sure we physically reenable interrupts here, no matter what
+                * the current task status is. This is important because if we
+                * are idle-spinning, we must allow interrupts, otherwise no
+                * process will ever wake up.
+                *
+                * During idle-spinning, an interrupt can occur and it may
+                * modify \p proc_ready_list. To ensure that compiler reload this
+                * variable every while cycle we call CPU_MEMORY_BARRIER.
+                * The memory barrier ensure that all variables used in this context
+                * are reloaded.
+                * \todo If there was a way to write sig_wait() so that it does not
+                * disable interrupts while waiting, there would not be any
+                * reason to do this.
+                */
+               IRQ_ENABLE;
+               CPU_IDLE;
+               MEMORY_BARRIER;
+               IRQ_DISABLE;
+       }
+       /*
+        * Optimization: don't switch contexts when the active process has not
+        * changed.
+        */
+       if (LIKELY(current_process != old_process)) {
+               cpu_stack_t *dummy;
+
+               /*
+                * Save context of old process and switch to new process. If
+                * there is no old process, we save the old stack pointer into
+                * a dummy variable that we ignore. In fact, this happens only
+                * when the old process has just exited.
+                */
+               asm_switch_context(&current_process->stack,
+                               old_process ? &old_process->stack : &dummy);
+       }
+       /* This RET resumes the execution on the new process */
+       LOG_INFO("resuming %p:%s\n", current_process, proc_currentName());
+}