From 43db8c57ebe496bea03d66e2ddd0aa6bc298738c Mon Sep 17 00:00:00 2001
From: Christian Cunningham <cc@localhost>
Date: Sun, 19 Dec 2021 14:50:45 -0800
Subject: Added atomic swap
---
src/cpu/atomic/swap.a.h | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
create mode 100644 src/cpu/atomic/swap.a.h
(limited to 'src')
diff --git a/src/cpu/atomic/swap.a.h b/src/cpu/atomic/swap.a.h
new file mode 100644
index 0000000..63dd50b
--- /dev/null
+++ b/src/cpu/atomic/swap.a.h
@@ -0,0 +1,32 @@
+#ifndef CPU_ATOMIC_SWAP_A_H
+#define CPU_ATOMIC_SWAP_A_H
+
+/// https://stackoverflow.com/questions/16329123/use-of-strexeq-instead-of-strex-for-spinlock-implementation-in-arm
+
+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_unlock(unsigned long* addr) {
+ unsigned long cleared = 0;
+ asm volatile(
+" dmb\n"
+" str %0, [%1]\n"
+" dsb\n"
+" sev"
+ :: "r" (cleared), "r" (addr)
+ : "cc");
+}
+
+#endif
--
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