LDDEC — Load with Autodecrement

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
LDDEC 1001000000 00000100
w 10
s 3210

Assembler Syntax

LDDEC mw, as

C Syntax

#include <xtensa/tie/xt_MAC16.h>

extern void XT_LDDEC(immediate w, const short * p /*inout*/);

Description

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

LDDEC loads MAC16 register mw from memory using auto-decrement addressing. It forms a virtual address by subtracting 4 from the contents of address register as. 32 bits (four bytes) are read from the physical address. This data is then written to MAC16 register mw, and the virtual address is written back to address register as.

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] − 4
(mem32, error) ← Load32(vAddr)
if error then
	EXCVADDR ← vAddr
	Exception (LoadStoreErrorCause)
else
	MR[w] ← mem32
	AR[s] ← vAddr
endif

Exceptions

Memory Load Group (see Memory Load Group:)

Implementation Pipeline

In Out
ars Estage mw Mstage, ars Estage

Protos that use LDDEC

proto LDDEC { in immediate w, inout const int16 * p }{}{
LDDEC w + 0, p;
}
proto SLDDEC { in immediate w, inout const int16 * p }{}{
LDDEC w + 0, p;
}
proto ULDDEC { in immediate w, inout const uint16 * p }{}{
LDDEC w + 0, p;
}