2. Topics
Introduction: What is PCI bus?
Introduction: What is PCI Express?
Difference between PCI and PCI Express
PCI Express: Architecture
PCI Express: Hardware basics
PCI Express: Configuration Space
PCI Express: Memory mapping
PCI Express: WEC7 driver basics
3. What is PCI bus?
Peripheral Component Interconnect (PCI) is a type of computer bus for attaching
hardware devices/peripherals in a computer.
It is a parallel bus, and devices connected to the PCI bus appear to a bus master to be
connected directly to its own bus.
PCI is used to connect computer
peripherals such as Graphic cards,
sound cards, network cards (Wi-Fi /
Ethernet), USB ports etc.
4. What is PCI bus?
PCI bus specifications were introduced by
Intel In July 1993.
It provides direct access to system
memory for connected devices.
PCI bus supports fixed width 32 bits, and
maximum of 5 devices can be connected.
PCI operated at 33 MHz using a 32-bit-
wide path.
Revisions to the standard include
increasing the speed from 33 MHz to 66
MHz and doubling the bit count to 64.
5. What is PCI bus?
PCI achieved popularity after the arrival of Windows 95 (in 1995).
This is due to the fact that Windows95 supported a feature called Plug and Play
(PnP).
Intel created the PnP standard and incorporated it into the design for PCI.
PCI-X:
PCI-X is extended version of PCI.
PCI-X provides for 64-bit transfers at a
speed of 133 MHz.
6. What is PCI Express?
PCI Express (Peripheral Component Interconnect Express), abbreviated as PCIe,
is a high-speed serial computer expansion bus standard designed to replace the older PCI
and PCI-X bus standards.
PCIe is having many improvements over the
older PCI/PCI-X such as:
Developed by Intel in 2004.
PCI Express is a serial interface, unlike PCI and PCI-X, which are parallel
interfaces.
Higher maximum system bus throughput, lower I/O pin count, smaller physical
footprint, better performance-scaling for bus devices, a more detailed error detection
and reporting mechanism (Advanced Error Reporting (AER)).
7. What are the differences between PCI
and PCI Express?
PCI PCI Express
Parallel Bus Serial Bus
Speed is 133MB/s to 533 MB/s Speed is 250 MB/s to several GB/s per
lane
Maximum of 5 End point devices can
be connected
Maximum of 32 devices can be
connected on each bus
Shared bus topology Point-to-point bus/
Shared switch topology
Hot plugging functionality is not
available
Hot plugging is supported
8. What are the differences between PCI
and PCI Express?
Difference in topology:
PCI : Parallel PCI Express: Serial
10. PCI Express Architecture
PCIe Root Complex:
In a PCI Express system, a root complex device connects the processor (and memory
subsystem) to the PCI Express End point devices or switch devices.
A root complex can be connected a maximum of 32 devices (Either end point device or
switch.)
The root complex generates transaction requests on behalf of the processor, which is
interconnected through a local bus.
Root complex functionality may be implemented as a discrete device, or may be
integrated with the processor.
11. PCI Express Architecture
PCIe End point device:
Endpoints are devices other than root complex and switches that are requesters or completers
of PCI Express transactions.
They are peripheral devices such as Ethernet, USB or graphics devices. Endpoints initiate
transactions as a requester or respond to transactions as a completer.
End point device will be connected to either root complex or switch.
Two types of endpoints exist, PCI Express (Native) endpoints and legacy
endpoints.
12. Some PCIe End point devices
Wi-Fi card Ethernet card Graphic card
USB ports
Audio card
13. PCI Express Architecture
PCIe Switch:
In a PCI Express system, a PCIe switch a device, which allows connection to multiple
end point devices.
Since PCI Express is a point-to-point serial interconnect standard, it requires a switch
to connect a single PCI express port from a processor to multiple end-points.
A PCIe switch will be connected to either root complex or another switch.
14. PCI Express Architecture
PCIe Bridges:
PCI Express bridges allow devices with other standards to be used in systems that need
to interoperate with PCI Express.
These bridges facilitate connection back to conventional PCI/PCI-X buses.
Applications using these bridge devices include servers, storage host bus adapters,
graphics, TV tuners and security systems.
15. PCI Express Architecture
Each end point device is identified by the combination of bus number, device number
and function number.
Function number:
PCI Express devices may support up to 8 functions per endpoint with at least one
function being number 0.
Device number:
Each bus can support up to 32 PCIe devices, which can be either switch or end point
device.
Bus number:
A system could theoretically include up to 256 buses. (Also called Links)
17. PCI Express Architecture
A Port is the interface between a PCI Express component and the bus, and
consists of differential transmitters and receivers.
An Upstream Port is a port that points in the direction of the root complex.
A Downstream Port is a port that points away from the root complex.
An endpoint port is therefore, by definition, always an upstream port, and A
root complex port(s) is a downstream port.
18. PCI Express Lanes
The PCIe link between two devices can
consist of anywhere from 1 to 32 lanes.
These are differentiated as x1, x2, x4, x8,
x16 and x32 PCIe links (and PCIe
connectors).
Each lane consists on two pair of wires,
one pair for receiving data, and another for
transmitting.
Each lane carries data of 1 bit/cycle.
So, transfer rate increases as number of
lanes increases.
19. PCI Express Connectors (PCIe Slots)
PCIe slot can be of types: x1, x2, x4,
x8, x16 or x32.
A connector of type x1 can be
connected in x2 slot, but the reverse is
not possible.
20. PCIe Configuration space
Software model of PCIe is same as older PCI/PCI-X.
So there will be no difference in the bus driver software model.
The PCI Express configuration model supports two mechanisms:
The PCI compatible configuration model, which is 100% compatible with old
PCI/PCI-X drivers and bus enumeration and configuration software for PCI/PCI-
X systems.
The PCI Express enhanced configuration mechanism which provides access to
additional configuration space beyond the first 256 Bytes, up to 4Kbytes per
function.
Enhanced configuration
contains the data that are
additional features for PCIe.
E.g: Link training (Linkup
detection)
Configuration space will be
according to PCIe v2.1.
Example is as shown:
21. PCIe Memory mapping
Memory mapping for PCIe has 3 main parts:
1.Config space
2.Memory space
3.I/O space
Config space may also contain all the PCIe
controller registers
(e.g. :Freescale’s iMX6Q)
Memory and I/O space of each device is
mapped into the respective memory areas on
RAM.
22. WEC7 PCIe driver
WEC7 PCIe driver mainly has 2
parts:
1.PCI bus driver (Provided by
Microsoft)
2.OAL PCIe configurations (Contains
PCIInit, PCIWriteCfg and
PCIReadCFg)
These functions used by PCI bus
driver for all PCIe operations.
23. WEC7 PCI Bus driver
PCI bus driver which is available with WEC7 installation in /public folder.
The driver flow is as follows:
Enumerate PCI bus
(Read cfg data including
VendorID and Device ID)
Configure PCI bus memory
mapping
(Allocate memory/IO
space for PCIe devices)
Launch the PCIe EP driver
(Compare Vid & Pid with
registry entries, and
launch corresponding
EPDriver.dll)
