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#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", "memory");
}
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", "memory");
}
#endif
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