test: Use SimpleMemory for atomic full-system tests

Keep it simple and use the SimpleMemory rather than the DRAM
controller model for atomic full-system tests.

config: Move the memory instantiation outside FSConfig

This patch moves the instantiation of the memory controller outside
FSConfig and instead relies on the mem_ranges to pass the information
to the caller (e.g. fs.py or one of the regression scripts). The main
motivation for this change is to expose the structural composition of
the memory system and allow more tuning and configuration without
adding a large number of options to the makeSystem functions.

The patch updates the relevant example scripts to maintain the current
functionality. As the order that ports are connected to the memory bus
changes (in certain regresisons), some bus stats are shuffled
around. For example, what used to be layer 0 is now layer 1.

Going forward, options will be added to support the addition of
multi-channel memory controllers.

tests: Create base classes to encapsulate common test configurations

Most of the test cases currently contain a large amount of duplicated
boiler plate code. This changeset introduces a set of classes that
encapsulates most of the functionality when setting up a test
configuration.

The following base classes are introduced:
* BaseSystem - Basic system configuration that can be used for both
SE and FS simulation.

* BaseFSSystem - Basic FS configuration uni-processor and multi-processor
configurations.

* BaseFSSystemUniprocessor - Basic FS configuration for uni-processor
configurations. This is provided as a way
to make existing test cases backwards
compatible.

Architecture specific implementations are provided for ARM, Alpha, and
X86.

config: Fix the cache class naming in regression scripts

This patch unifies the naming of the default L1 and L2 caches in the
regression configs to be in line with what is used in the se and fs
scripts.

config: Use shared cache config for regressions

This patch uses the common L1, L2 and IOCache configuration for the
regressions that all share the same cache parameters. There are a few
regressions that use a slightly different configuration (memtest,
o3-timing=mp, simple-atomic-mp and simple-timing-mp), and the latter
are not changed in this patch. They will be updated in a future patch.

The common cache configurations are changed to match the ones used in
the regressions, and are slightly changed with respect to what they
were. Hopefully this means we can converge on a common base
configuration, used both in the normal user configurations and
regressions.

As only regressions that shared the same cache configuration are
updated, no regressions are affected.

Mem: Use cycles to express cache-related latencies

This patch changes the cache-related latencies from an absolute time
expressed in Ticks, to a number of cycles that can be scaled with the
clock period of the caches. Ultimately this patch serves to enable
future work that involves dynamic frequency scaling. As an immediate
benefit it also makes it more convenient to specify cache performance
without implicitly assuming a specific CPU core operating frequency.

The stat blocked_cycles that actually counter in ticks is now updated
to count in cycles.

As the timing is now rounded to the clock edges of the cache, there
are some regressions that change. Plenty of them have very minor
changes, whereas some regressions with a short run-time are perturbed
quite significantly. A follow-on patch updates all the statistics for
the regressions.

Regression: Use addTwoLevelCacheHierarchy in configs

This patch unifies the full-system regression config scripts and uses
the BaseCPU convenience method addTwoLevelCacheHierarchy to connect up
the L1s and L2, and create the bus inbetween.

The patch is a step on the way to use the clock period to express the
cache latencies, as the CPU is now the parent of the L1, L2 and L1-L2
bus, and these modules thus use the CPU clock.

The patch does not change the value of any stats, but plenty names,
and a follow-up patch contains the update to the stats, chaning
system.l2c to system.cpu.l2cache.

Cache: add a response latency to the caches

In the current caches the hit latency is paid twice on a miss. This patch lets
a configurable response latency be set of the cache for the backward path.

Bus: Split the bus into a non-coherent and coherent bus

This patch introduces a class hierarchy of buses, a non-coherent one,
and a coherent one, splitting the existing bus functionality. By doing
so it also enables further specialisation of the two types of buses.

A non-coherent bus connects a number of non-snooping masters and
slaves, and routes the request and response packets based on the
address. The request packets issued by the master connected to a
non-coherent bus could still snoop in caches attached to a coherent
bus, as is the case with the I/O bus and memory bus in most system
configurations. No snoops will, however, reach any master on the
non-coherent bus itself. The non-coherent bus can be used as a
template for modelling PCI, PCIe, and non-coherent AMBA and OCP buses,
and is typically used for the I/O buses.

A coherent bus connects a number of (potentially) snooping masters and
slaves, and routes the request and response packets based on the
address, and also forwards all requests to the snoopers and deals with
the snoop responses. The coherent bus can be used as a template for
modelling QPI, HyperTransport, ACE and coherent OCP buses, and is
typically used for the L1-to-L2 buses and as the main system
interconnect.

The configuration scripts are updated to use a NoncoherentBus for all
peripheral and I/O buses.

A bit of minor tidying up has also been done.

cache: Allow main memory to be at disjoint address ranges.

CPU: Check that the interrupt controller is created when needed

This patch adds a creation-time check to the CPU to ensure that the
interrupt controller is created for the cases where it is needed,
i.e. if the CPU is not being switched in later and not a checker CPU.

The patch also adds the "createInterruptController" call to a number
of the regression scripts.

MEM: Introduce the master/slave port roles in the Python classes

This patch classifies all ports in Python as either Master or Slave
and enforces a binding of master to slave. Conceptually, a master (such
as a CPU or DMA port) issues requests, and receives responses, and
conversely, a slave (such as a memory or a PIO device) receives
requests and sends back responses. Currently there is no
differentiation between coherent and non-coherent masters and slaves.

The classification as master/slave also involves splitting the dual
role port of the bus into a master and slave port and updating all the
system assembly scripts to use the appropriate port. Similarly, the
interrupt devices have to have their int_port split into a master and
slave port. The intdev and its children have minimal changes to
facilitate the extra port.

Note that this patch does not enforce any port typing in the C++
world, it merely ensures that the Python objects have a notion of the
port roles and are connected in an appropriate manner. This check is
carried when two ports are connected, e.g. bus.master =
memory.port. The following patches will make use of the
classifications and specialise the C++ ports into masters and slaves.

SE/FS: Make SE vs. FS mode a runtime parameter.

MEM: Make the bus bridge unidirectional and fixed address range

This patch makes the bus bridge uni-directional and specialises the
bus ports to be a master port and a slave port. This greatly
simplifies the assumptions on both sides as either port only has to
deal with requests or responses. The following patches introduce the
notion of master and slave ports, and would not be possible without
this split of responsibilities.

In making the bridge unidirectional, the address range mechanism of
the bridge is also changed. For the cases where communication is
taking place both ways, an additional bridge is needed. This causes
issues with the existing mechanism, as the busses cannot determine
when to stop iterating the address updates from the two bridges. To
avoid this issue, and also greatly simplify the specification, the
bridge now has a fixed set of address ranges, specified at creation
time.

ARM: Add some MP regressions and clean up the disk images and kernels a bit

Mem: Fix issue with dirty block being lost when entire block transferred to non-cache.

This change fixes the problem for all the cases we actively use. If you want to try
more creative I/O device attachments (E.g. sharing an L2), this won't work. You
would need another level of caching between the I/O device and the cache
(which you actually need anyway with our current code to make sure writes
propagate). This is required so that you can mark the cache in between as
top level and it won't try to send ownership of a block to the I/O device.
Asserts have been added that should catch any issues.

ARM: Clarifies creation of Linux and baremetal ARM systems.

makeArmSystem creates both bare-metal and Linux systems more cleanly.
machine_type was never optional though listed as an optional argument; a system
such as "RealView_PBX" must now be explicitly specified. Now that it is a
required argument, the placement of the arguments has changed slightly
requiring some changes to calls that create ARM systems.

Config: Keep track of uncached and cached ports separately.

This makes sure that the address ranges requested for caches and uncached ports
don't conflict with each other, and that accesses which are always uncached
(message signaled interrupts for instance) don't waste time passing through
caches.

ARM: Add full-system regressions