stdlib: Move `_connect_things` to run as pre_instantiation

Through working with the gem5 stdlib there have been instances where
connecting the memory, processor, and cache hierarchy to the board (via
the AbstractBoard's `_connect_things` function) at the point of the
AbstractBoard's construction is problematic as the memory, processor,
and cache hierarchy may require information to connect correctly that is
only known to the AbstractBoard after construction. In particular this
can occur when a Workload contains information needed to configure

To resolve this problem the `_connect_things` function has been moved to
run as a pre-initialization step. That is, run immediately before
`m5.instantiate`. This is done in the Simulator module.

This will break cases where a user utilizes the stdlib AbstractBoard but
does not use the stdlib Simulator module. As such, an Exception is
raised in these cases explaining the fix to the user. This is done via a
hack where the boards' `createCCObject` function (inheritted
from SimObject) is overriden with a check to ensure `_connect_things`
has been run. To fix the `_pre_instantiate` function must be executed
prior to `m5.instantiate` in the Python configuration script. Test and
config scripts in the gem5 repo have been updated accordingly.

Change-Id: Ibaef36eb7433ce104b861b1da80fc600f08f715a
Maintainer: Bobby Bruce <>
Reviewed-by: Giacomo Travaglini <>
Reviewed-by: Jason Lowe-Power <>
Tested-by: kokoro <>
11 files changed