VR4102 datasheet(189/701 Pages) NEC

189 / 701 page

CHAPTER 6 EXCEPTION PROCESSING

189

6.4.16 Integer Overflow Exception

Cause

An Integer Overflow exception occurs when an ADD, ADDI, SUB, DADD, DADDI or DSUB instruction results in a

2’s complement overflow. This exception is not maskable.

Processing

The common exception vector is used for this exception, and the Ov code in the ExcCode field of the Cause

The EPC register contains the address of the instruction that caused the exception unless the instruction is in a

branch delay slot, in which case the EPC register contains the address of the preceding branch instruction and

the BD bit of the Cause register is set to 1.

Servicing

At the time of the exception, the kernel reports the UNIX SIGFPE/FPE_INTOVF_TRAP (floating-point

exception/integer overflow) signal to the current process, and this exception is usually fatal.

6.4.17 Watch Exception

Cause

A Watch exception occurs when a load or store instruction references the physical address specified by the

WatchLo/WatchHi registers. The WatchLo/WatchHi registers specify whether a load or store or both could have

initiated this exception.

When the R bit of the WatchLo register is set to 1: Load instruction

When the W bit of the WatchLo register is set to 1: Store instruction

When both the R bit and W bit of the WatchLo register are set to 1: Load instruction or store instruction

The CACHE instruction never causes a Watch exception.

The Watch exception is postponed while the EXL bit in the Status register is set to 1, and Watch exception is only

maskable by setting the EXL bit in the Status register to 1.

Processing

The common exception vector is used for this exception, and the WATCH code in the ExcCode field of the Cause

The EPC register contains the address of the load or store instruction that caused the exception unless it is in a

branch delay slot, in which case the EPC register contains the address of the preceding branch instruction and

the BD bit of the Cause register is set to 1.

VR4102 Datasheet(PDF) 189 Page - NEC