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-rw-r--r--include/cpu/atomic/swap.h40
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