L32AI — Load 32-bit Acquire

Instruction Word

Slot
Inst
6
3
6
2
6
1
6
0
5
9
5
8
5
7
5
6
5
5
5
4
5
3
5
2
5
1
5
0
4
9
4
8
4
7
4
6
4
5
4
4
4
3
4
2
4
1
4
0
3
9
3
8
3
7
3
6
3
5
3
4
3
3
3
2
3
1
3
0
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
1
1
0
9876543210
Format x24 - 24 bit(s) 0
L32AI 1011 0010
t 3210
s 3210
imm8 76543210

Assembler Syntax

L32AI at, as, 0..1020

C Syntax

#include <xtensa/tie/xt_sync.h>

extern unsigned XT_L32AI(const unsigned * p, immediate o);

Description

(please consult the Xtensa ® Instruction Set Architecture Reference Manual for any cross references and additional information)

L32AI is a 32-bit load from memory with "acquire" semantics. This load performs before any subsequent loads, stores, acquires, or releases are performed. It is typically used to test a synchronization variable protecting a critical region (for example, to acquire a lock).

L32AI forms a virtual address by adding the contents of address register as and an
8-bit zero-extended constant value encoded in the instruction word shifted left by two. Therefore, the offset can specify multiples of four from zero to 1020. 32 bits (four bytes) are read from the physical address. This data is then written to address register at. L32AI causes the processor to delay processing of subsequent loads, stores, acquires, and releases until the L32AI is performed. In some Xtensa ISA implementations, this occurs automatically and L32AI is identical to L32I. Other implementations (for example, those with multiple outstanding loads and stores) delay processing as described above. Because the method of delay is implementation-dependent, this is indicated in the operation section below by the implementation function acquire.

If the Region Translation Option or the MMU Option is enabled, the virtual address is translated to the physical address. If not, the physical address is identical to the virtual address. If the translation or memory reference encounters an error (for example, protection violation or non-existent memory), the processor raises one of several exceptions .

Without the Unaligned Exception Option , the two least significant bits of the address are ignored. A reference to an address that is not 0 mod 4 produces the same result as a reference to the address with the least significant bits cleared. With the Unaligned Exception Option, such an access raises an exception.

Operation

vAddr ← AR[s] + (022||imm8||02)
(mem32, error) ← Load32(vAddr)
if error then
	EXCVADDR ← vAddr
	Exception (LoadStoreErrorCause)
else
	AR[t] ← mem32
	acquire
endif

Exceptions

Memory Load Group (see Memory Load Group:)

Protos that use L32AI

proto L32AI { out uint32 c, in const uint32 * p, in immediate o }{}{
L32AI c, p, o + 0;
}