IIU — Instruction Cache Index Unlock

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
IIU 00110111 11010010
s 3210
op2 3210

Assembler Syntax

IIU as, 0..240

C Syntax

#include <xtensa/tie/xt_instcache.h>

extern void XT_IIU(int s, immediate i);

Description

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

IIU uses the virtual address to choose a location in the instruction cache and unlocks the chosen line. The purpose of IIU is to remove the lock created by an IPFL instruction. The method for mapping the virtual address to an instruction cache location is implementation-specific. This instruction is primarily useful for unlocking the entire instruction cache. Xtensa ISA implementations that do not implement cache locking must raise an illegal instruction exception when this opcode is executed. In some implementations, IIU invalidates the cache line in addition to unlocking it.

To unlock a specific cache line if it is in the cache, use the IHU instruction.

IIU forms a virtual address by adding the contents of address register as and a 4-bit zero-extended constant value encoded in the instruction word shifted left by four. Therefore, the offset can specify multiples of 16 from zero to 240. The virtual address chooses a cache line without translation and without raising the associated exceptions.

Because the organization of caches is implementation-specific, the operation section below specifies only a call to the implementation's iindexunlock function.

IIU is a privileged instruction.

Operation

if CRING != 0 then
	Exception (PrivilegedCause)
else
	vAddr ← AR[s] + (024||imm4||04)
	iindexunlock(vAddr)
endif

Exceptions

EveryInstR Group (see EveryInstR Group:)GenExcep(PrivilegedCause) if Exception OptionMemoryErrorException if Memory ECC/Parity Option

Protos that use IIU

proto IIU { in int32 s, in immediate i }{}{
IIU s, i + 0;
}