DocID025623 Rev 2

9/22

AN4417

Machine check handler

21

2.1.1

Start phase

In the first step the hardware (Core) carries out checks, when the machine occurs

exception. The hardware stores content of the MSR register and address of the current

instruction pointer if it is possible (precise exception), low level driver immediately starts

processing.The machine executes several steps like check status register saving, context of

the interrupted process saving and others. This part stores some additional information as

they are used by higher layer user handler to analyze the root cause of the exception later.

In the Z4 Core User Manual documentation is described a detailed description of the

machine check resources, their meaning and proper handling in case of interrupt. Low level

handler follows rules and recommendation described in the User Manual (see

Section Appendix B: Reference documents).

2.1.2

Final phase

Here the handler should restore the saved context of the interrupted process and return with

the mcrfi instruction.

Before mcrfi instruction is executed, which fills instruction pointer with MCSRR0 content and

MSR register with MCSRR1 content, MCSRR0 modification might be needed.

There are two cases which determine if the manipulation is needed or not. This information

is useful in the user handler to pass down to the low level driver.

1.

User handler finds the cause of the machine check exception and fix it in a way, that

the program can re-execute the same instruction that caused the machine check

exception.

2.

User is able to find the cause of the exception, but the problem remains and re-

executing the same instruction lead to the machine check exception again =>

Modification of the MCSRR0 is needed.

2.1.3

Modification of the MCSRR0 register

In case that the cause of the exception cannot be removed, MCSRR0 register value is

modified in a way that it takes the address of the following instruction. This prevents re-

execution of the faulty instruction and retriggering the machine check exception.

Modification has to consider VLE instruction coding in case the interrupted process is

implemented in VLE coding and increment the value accordingly of the length of the faulty

instruction pointed by the current MCSRR0 register content, see Figure 2.