sched: add idle task

arch/at91sam3x8e/sched.c

@@ -5,15 +5,17 @@
 #include <arch/interrupt.h>
 
 #include <ardix/atomic.h>
+#include <ardix/malloc.h>
 #include <ardix/sched.h>
 
+#include <errno.h>
 #include <string.h>
 
 void handle_sys_tick(void)
 {
 	/*
 	 * fire a PendSV exception and do the actual context switching there
-	 * because it is faster that way (according to the docs, at least)
+	 * because the docs say you're supposed to do it that way
 	 */
 	if (!is_atomic_context())
 		arch_irq_invoke(IRQNO_PEND_SV);
@@ -55,7 +57,7 @@ int arch_sched_hwtimer_init(unsigned int freq)
 	return 0;
 }
 
-void arch_sched_task_init(struct task *task, void (*entry)(void))
+void arch_task_init(struct task *task, void (*entry)(void))
 {
 	struct reg_snapshot *regs = task->stack_bottom - sizeof(*regs);
 	task->sp = regs;
@@ -73,6 +75,29 @@ void yield(enum task_state state)
 	arch_irq_invoke(IRQNO_PEND_SV);
 }
 
+__naked __noreturn static void idle_task_entry(void)
+{
+	__asm__ volatile(
+"1:	b	1b	\n"
+	:::
+	);
+}
+
+int arch_idle_task_init(struct task *task)
+{
+	void *sp = malloc(sizeof(struct reg_snapshot));
+	if (sp == NULL)
+		return -ENOMEM;
+
+	task->stack_bottom = sp + sizeof(struct reg_snapshot);
+	arch_task_init(task, idle_task_entry);
+	task->lastexec = 0;
+	task->sleep_usecs = 0;
+	task->state = TASK_READY;
+	task->pid = -1;
+	return 0;
+}
+
 /*
  * This file is part of Ardix.
  * Copyright (c) 2020, 2021 Felix Kopp <owo@fef.moe>.

arch/at91sam3x8e/serial.c

@@ -133,6 +133,12 @@ void irq_uart(void)
 	if (state & REG_UART_SR_RXRDY_MASK) {
 		tmp = REG_UART_RHR;
 		ringbuf_write(arch_serial_default_device.device.rx, &tmp, sizeof(tmp));
+
+		/* TODO: we need some error handling mechanism for event creation */
+		struct device_kevent *event = device_kevent_create(&serial_default_device->device,
+								   DEVICE_CHANNEL_IN);
+		if (event != NULL)
+			kevent_dispatch(&event->event);
 	}
 
 	/* REG_UART_PDC_TCR has reached zero */
@@ -146,6 +152,12 @@ void irq_uart(void)
 
 		if (arch_serial_default_device.tx_current == NULL)
 			REG_UART_IDR = REG_UART_IDR_ENDTX_MASK;
+
+		/* TODO: we need some error handling mechanism for event creation */
+		struct device_kevent *event = device_kevent_create(&serial_default_device->device,
+								   DEVICE_CHANNEL_OUT);
+		if (event != NULL)
+			kevent_dispatch(&event->event);
 	}
 
 	/* check for error conditions */

include/arch-generic/sched.h

@@ -6,7 +6,7 @@
 
 #include <toolchain.h>
 
-struct process; /* see include/ardix/sched.h */
+struct task; /* see include/ardix/sched.h */
 
 /**
  * Initialize a hardware timer for schduling.
@@ -23,7 +23,9 @@ int arch_sched_hwtimer_init(unsigned int freq);
  * @param process: The process.
  * @param entry: The process entry point.
  */
-void arch_sched_process_init(struct process *process, void (*entry)(void));
+void arch_task_init(struct task *task, void (*entry)(void));
+
+int arch_idle_task_init(struct task *task);
 
 /*
  * This file is part of Ardix.

kernel/sched.c

@@ -18,6 +18,8 @@ extern uint32_t _estack;
 static struct task *tasktab[CONFIG_SCHED_MAXTASK];
 struct task *current;
 
+static struct task idle_task;
+
 static void task_destroy(struct kent *kent)
 {
 	struct task *task = container_of(kent, struct task, kent);
@@ -36,27 +38,35 @@ int sched_init(void)
 	current->kent.parent = kent_root;
 	current->kent.destroy = task_destroy;
 	i = kent_init(&current->kent);
-	if (i == 0) {
-		current->sp = &_sstack;
-		current->stack_bottom = &_estack;
-		current->pid = 0;
-		current->state = TASK_READY;
-		tasktab[0] = current;
+	if (i != 0)
+		goto out;
 
-		for (i = 1; i < CONFIG_SCHED_MAXTASK; i++)
-			tasktab[i] = NULL;
+	current->sp = &_sstack;
+	current->stack_bottom = &_estack;
+	current->pid = 0;
+	current->state = TASK_READY;
+	tasktab[0] = current;
 
-		i = arch_watchdog_init();
+	for (i = 1; i < CONFIG_SCHED_MAXTASK; i++)
+		tasktab[i] = NULL;
 
-		if (i == 0)
-			i = arch_sched_hwtimer_init(CONFIG_SCHED_FREQ);
-	}
+	i = arch_watchdog_init();
+	if (i != 0)
+		goto out;
+
+	i = arch_sched_hwtimer_init(CONFIG_SCHED_FREQ);
+	if (i != 0)
+		goto out;
+
+	i = arch_idle_task_init(&idle_task);
+	if (i != 0)
+		goto out;
 
 	/*
 	 * we don't really need to deallocate resources on error because we
 	 * are going to panic anyways if the scheduler fails to initialize.
 	 */
-
+out:
 	return i;
 }
 
@@ -66,37 +76,36 @@ int sched_init(void)
  * @param task: the task
  * @returns whether `task` could be run next
  */
-static inline bool sched_task_should_run(const struct task *task)
+static inline bool can_run(const struct task *task)
 {
 	enum task_state state = task->state;
-
-	if (state == TASK_QUEUE || state == TASK_READY || state == TASK_IOWAIT)
-		return true;
-
-	return false;
+	return state == TASK_QUEUE || state == TASK_READY;
 }
 
 void *sched_process_switch(void *curr_sp)
 {
 	struct task *tmp;
+	int i;
 	pid_t nextpid = current->pid;
 	current->sp = curr_sp;
 
 	if (current->state != TASK_SLEEP && current->state != TASK_IOWAIT)
 		current->state = TASK_QUEUE;
 
-	while (1) {
+	for (i = 0; i < CONFIG_SCHED_MAXTASK; i++) {
 		nextpid++;
 		nextpid %= CONFIG_SCHED_MAXTASK;
 
 		tmp = tasktab[nextpid];
-		if (tmp != NULL && sched_task_should_run(tmp)) {
+		if (tmp != NULL && can_run(tmp)) {
 			current = tmp;
 			break;
 		}
-		/* TODO: Add idle thread */
 	}
 
+	if (i == CONFIG_SCHED_MAXTASK)
+		current = &idle_task;
+
 	current->state = TASK_READY;
 	return current->sp;
 }