The NULL ISA doesn't actually have registers, so this setting doesn't matter. By making it 64 bits the ISA is more compatible with the other ISAs. Change-Id: I2c9b6d9a6f612719b8b00eb9dbed55fa2159e9b5 Reviewed-on: https://gem5-review.googlesource.com/c/13617 Reviewed-by: Jason Lowe-Power <jason@lowepower.com> Maintainer: Jason Lowe-Power <jason@lowepower.com>