Enable SysTick on sched_init

arch/at91sam3x8e/Makefile

@@ -27,6 +27,7 @@ ARDIX_ARCH_PWD = $(PWD)/arch/at91sam3x8e
 
 ARDIX_SOURCES += \
 	$(ARDIX_ARCH_PWD)/isr_sched.c \
+	$(ARDIX_ARCH_PWD)/sched_hwtimer.c \
 	$(ARDIX_ARCH_PWD)/startup.c
 
 ARDIX_ASM_SOURCES += \

arch/at91sam3x8e/sched_hwtimer.c

@@ -0,0 +1,54 @@
+/*
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 2020 Felix Kopp <sandtler@sandtler.club>
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ *    conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ *    conditions and the following disclaimer in the documentation and/or other materials
+ *    provided with the distribution.
+ * 3. Neither the name of the copyright holder nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software without specific prior
+ *    written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <arch/sched.h>
+#include <arch/at91sam3x8e/hardware.h>
+
+int sched_hwtimer_init(unsigned int freq)
+{
+	uint32_t ticks = F_CPU / freq;
+	if (ticks > REG_SYSTICK_LOAD_RELOAD_MASK)
+		return 1;
+
+	REG_SYSTICK_LOAD = (ticks & REG_SYSTICK_LOAD_RELOAD_MASK) - 1;
+	REG_SYSTICK_VAL = 0U;
+	REG_SYSTICK_CTRL = REG_SYSTICK_CTRL_CLKSOURCE_MASK
+			 | REG_SYSTICK_CTRL_TICKINT_MASK
+			 | REG_SYSTICK_CTRL_ENABLE_MASK;
+
+	return 0;
+}
+
+void sched_hwtimer_pause(void)
+{
+	REG_SYSTICK_CTRL &= ~REG_SYSTICK_CTRL_ENABLE_MASK;
+}
+
+void sched_hwtimer_resume(void)
+{
+	REG_SYSTICK_CTRL |= REG_SYSTICK_CTRL_ENABLE_MASK;
+}

arch/at91sam3x8e/startup.c

@@ -143,8 +143,8 @@ __section(.vectors) const void *exception_table[] = {
 	&isr_svc,		/* SVC call (used for syscalls) */
 	&isr_debug_mon,		/* reserved for debug */
 	NULL,			/* reserved */
-	&isr_pend_sv,		/* PendSV */
-	&isr_sys_tick,		/* SysTick (used by the scheduler) */
+	&isr_pend_sv,		/* PendSV (used by the scheduler) */
+	&isr_sys_tick,		/* SysTick */
 
 	/*
 	 * Ok I am REALLY tired of writing out mnemonics.

include/arch/sched.h

@@ -0,0 +1,45 @@
+/*
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 2020 Felix Kopp <sandtler@sandtler.club>
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ *    conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ *    conditions and the following disclaimer in the documentation and/or other materials
+ *    provided with the distribution.
+ * 3. Neither the name of the copyright holder nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software without specific prior
+ *    written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+/**
+ * Initialize a hardware timer for schduling.
+ *
+ * @param freq: The timer frequency in Hertz.
+ */
+int sched_hwtimer_init(unsigned int freq);
+
+/**
+ * Temporarily pause the scheduling timer (for atomic contexts).
+ */
+void sched_hwtimer_pause(void);
+
+/**
+ * Resume the previously paused scheduling timer.
+ */
+void sched_hwtimer_resume(void);

kernel/sched.c

@@ -25,6 +25,7 @@
  * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <arch/sched.h>
 #include <ardix/clock.h>
 #include <ardix/sched.h>
 #include <ardix/types.h>
@@ -53,9 +54,9 @@ int sched_init(void)
 		procs[i].pid = -1;
 	}
 
-	/* TODO: initialize SysTick */
+	i = sched_hwtimer_init(10000);
 
-	return 0;
+	return i;
 }
 
 void *sched_process_switch(void *curr_sp)
@@ -65,7 +66,7 @@ void *sched_process_switch(void *curr_sp)
 
 	while (true) {
 		nextproc = nextproc->next;
-		if (nextproc->state == PROC_QUEUE) {
+		if (nextproc->state == PROC_QUEUE || nextproc->state == PROC_READY) {
 			_current_process->state = PROC_QUEUE;
 			nextproc->state = PROC_READY;
 			_current_process = nextproc;