1 files changed, 40 insertions, 0 deletions
diff --git a/include/cpu/atomic/swap.h b/include/cpu/atomic/swap.h
new file mode 100644
index 0000000..cbed62c
--- /dev/null
+++ b/include/cpu/atomic/swap.h
@@ -0,0 +1,40 @@
+#ifndef CPU_ATOMIC_SWAP_A_H
+#define CPU_ATOMIC_SWAP_A_H
+#include "../../util/mutex.h"
+
+/// https://stackoverflow.com/questions/16329123/use-of-strexeq-instead-of-strex-for-spinlock-implementation-in-arm
+/// https://elixir.bootlin.com/linux/v4.9/source/arch/arm/include/asm/spinlock.h
+/// https://elixir.bootlin.com/linux/v4.9/source/arch/arm/include/asm/spinlock_types.h#L23
+/// https://www.cs.uic.edu/~jbell/CourseNotes/OperatingSystems/3_Processes.html
+/// https://developer.arm.com/documentation/dht0008/a/arm-synchronization-primitives/practical-uses/implementing-a-semaphore?lang=en
+
+// TODO: Once scheduling works, have a failed lock put thread in waiting state
+static inline void atm_lock(unsigned long pid, unsigned long* addr)
+{
+	unsigned long tmp, current_lock_value;
+	asm volatile(
+"1:	ldrex	%0, [%3]\n"
+"	cmp	%0, #0\n"
+"	wfene\n"
+"	strexeq	%1, %2, [%3]\n"
+"	teq	%1, #0\n"
+"	bne	1b\n"
+"	dmb"
+	: "=&r" (current_lock_value), "=&r" (tmp)
+	: "r" (pid), "r" (addr)
+	: "cc");
+}
+
+static inline void atm_release(unsigned long* addr)
+{
+	unsigned long cleared = NULL_PID;
+	asm volatile(
+"	dmb\n"
+"	str %0, [%1]\n"
+"	dsb\n"
+"	sev"
+	:: "r" (cleared), "r" (addr)
+	: "cc");
+}
+
+#endif