Z4 Core exception overview

AN4367

6/13

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Machine check syndrome register (MCSR)

This register is the first register to check as it collects additional information about the cause

of the exception. There are three groups of machine check causes

Machine check address register (MCAR)

MCAR register contains target address reporting the fault condition. It is updated only for

Asynchronous Machine check group when MCSR.MAV bit is cleared and it is valid only if

MCSR.MAV status flag is set. Otherwise the MCAR register cannot be used in the fault

analysis.

It is important to clear MCSR.MAV bit after reading MCAR register value to enable capture

of the address in case of new asynchronous machine check fault.

Machine check MCSRR0 register

This register is updated by the HW in the beginning of the machine check interrupt. It stores

the address of the instruction that caused the error condition.

It is used in the end of the machine check when mcrfi instruction is executed to fill the

instruction pointer. The result is that code restarts the same instruction that was cause of the

error, if additional modification of the MCSRR0 register is not explicitly done.

MCSRR0 (Save/Restore register)

Address of the instruction that caused the exception. Once the

exception is finished (mcrfi instruction), program starts execution with

the same instruction, that was the cause of the exception.

Table 2. Machine check register (continued)

Register

Content

Table 3. Machine check causes

Machine check cause

Brief description

Error Report Machine check

(IF,LD,ST,G)

These exceptions are directly associated with the current instruction execution

taken whenever the condition occurs. They enable to differentiate between

Instruction fetch, Data store and load.

Non-maskable interrupt

(NMI)

pin is driven low.

Asynchronous Machine check

(BUS_IREER, BUS_DRERR,

BUS_WRERR)

Exceptions reported by the subsystem, usually as bus error termination, back to

machine check exception group triggers capture of the corresponding address to

then the MCAR register is not affected.