e32atomics.h File Reference

Detailed Description

General purpose atomic operations and utility functions All functions in this header are available on both user and kernel side.

Atomic operations: __e32_atomic_xxx_yyy8() should be used for 8 bit atomic variables __e32_atomic_xxx_yyy16() should be used for 16 bit atomic variables __e32_atomic_xxx_yyy32() should be used for 32 bit atomic variables __e32_atomic_xxx_yyy64() should be used for 64 bit atomic variables __e32_atomic_xxx_yyy_ptr() should be used for atomic updates to pointers

xxx specifies the operation performed load read memory atomically store write memory atomically swp write to a memory location and return the original value of the memory location add add a value to a memory location and return the original value of the memory location and bitwise AND a value with a memory location and return the original value of the memory location ior bitwise OR a value with a memory location and return the original value of the memory location xor bitwise XOR a value with a memory location and return the original value of the memory location axo atomic { orig_v = *p; *p = (orig_v & u) ^ v; } return orig_v; cas if the value of a memory location matches a specified expected value, write a specified new value and return TRUE, otherwise update the expected value with the actual value seen and return FALSE. tau if the value of a memory location is >= a specified threshold, considered as an unsigned integer, add a specified value to it otherwise add a different specified value to it; return the original value of the memory location tas if the value of a memory location is >= a specified threshold, considered as a signed integer, add a specified value to it otherwise add a different specified value to it; return the original value of the memory location

yyy specifies the memory ordering: rlx = relaxed memory ordering there is no guarantee on the order in which the atomic operation is observed relative to preceding or following memory accesses acq = acquire semantics the atomic operation is guaranteed to be observed before any following memory accesses rel = release semantics the atomic operation is guaranteed to be observed after any preceding memory accesses ord = fully ordered the atomic operation is guaranteed to be observed after any preceding memory accesses and before any following memory accesses

Note that these operations should only be used on normal memory regions since they are implemented in terms of LDREX/STREX and so multiple reads can occur before the operation completes. Also __e32_atomic_load_yyy64() can't be used on read-only memory regions since it uses LDREXD/STREXD to guarantee atomicity. Atomic operations may only be used on naturally aligned memory (i.e. *16() operations on an even address, *32() operations on an address which is a multiple of 4 and *64() operations on an address which is a multiple of 8). This applies even if you have (unwisely) decided to turn off alignment checking.

Barrier operations: Two barrier functions are provided: __e32_memory_barrier() - this ensures all preceding explicit memory accesses are observed before any following explicit memory accesses. Equates to the ARM DMB instruction. __e32_io_completion_barrier() - this ensures all preceding explicit memory accesses complete before any following instructions execute. For example, it ensures that writes to I/O devices have actually occurred before execution continues. Equates to the ARM DSB instruction.

Utility functions: __e32_find_ms1_32 Return bit position of most significant 1 in a 32 bit argument, or -1 if the argument is zero. __e32_find_ls1_32 Return bit position of least significant 1 in a 32 bit argument, or -1 if the argument is zero. __e32_bit_count_32 Return the count of bits set to 1 in a 32 bit argument. __e32_find_ms1_64 Return bit position of most significant 1 in a 64 bit argument, or -1 if the argument is zero. __e32_find_ls1_64 Return bit position of least significant 1 in a 64 bit argument, or -1 if the argument is zero. __e32_bit_count_64 Return the count of bits set to 1 in a 64 bit argument.