Hi all,
It's been a while that I am lingering about the idea of proposing a signature
change for the ISAs MiscReg setter:
What it currently is:
* void setMiscReg(int misc_reg, const MiscReg &val);
What I would like to have:
* Fault setMiscReg(int misc_reg, const MiscReg &val);
IMO this will improve system register access design, and will make it easier to
cover cases where the access to a System register produces a a fault as a side
effect.
This could be for instance a register access that is trapped or the setting of
a particular Bit in a system register which triggers an exception.
At the moment the current signature imposes us to have multiple table walks for
a specific
MiscReg number: when writing a system register I have to do the following calls
(this is ISA agnostic pseudocode)
1) checkIfTraps(miscreg_number);
Which will be implemented more or less in this way:
Switch(miscreg_number) {
Case MISCREG_1:
// return boolean or fault if trapping
Case MISCREG_2:
[…]
}
2) setMiscReg(miscreg_number, val);
Which will be implemented more or less in this way:
Switch(miscreg_number) {
Case MISCREG_1:
// Here I do the register masking for writing
Case MISCREG_2:
[…]
}
This could be inefficient because you have to traverse switch cases twice. This
is even more
True if the exception is generated by the write of a specific value in a
bitfield: other problems arise
If you have to generate the fault but still perform a register write.
Switching to
Fault setMiscReg(int misc_reg, const MiscReg &val);
Will be more callback oriented and solve the issue:
Do you have any thoughts about this? I'd like to have your opinion before
I start working on this big change.
Thanks
Giacomo Travaglini
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