6.15.12 PCIe

The Peripheral Component Interconnect Express (PCIe) module is a multi-lane I/O interconnect that provides low pin-count, high reliability, and high-speed data transfer at rates of up to 5.0 Gbps per lane, per direction, for serial links on backplanes and printed wiring boards. It is a 3-rd Generation I/O Interconnect technology succeeding PCI and ISA bus that is designed to be used as a general-purpose serial I/O interconnect. It is also used as a bridge to other interconnects like USB2/3.0, GbE MAC, and so forth.

The PCI Express standard predecessor - PCI, is a parallel bus architecture that is increasingly difficult to scale-up in bandwidth, which is usually performed by increasing the number of data signal lines. The PCIe architecture was developed to help minimize I/O bus bottlenecks within systems and to provide the necessary bandwidth for high-speed, chip-to-chip, and board-to-board communications within a system. It is designed to replace the PCI-based shared, parallel bus signaling technology that is approaching its practical performance limits while simplifying the interface design.

The device instantiates two PCIe subsystems (PCIe_SS1 and PCIe_SS2). The PCIe controller is capable to operate either in Root Complex (RC) or in End Point (EP) PCIe mode. The device PCIe_SS1 controller supports up to two 16-bit data lanes on its PIPE port. The device PCIe_SS2 controller supports only one 16-bit data lane on its PIPE port.

When the PCIe_SS1 controller PIPE port is configured to operate in a single-lane mode, it operates on a single pair of PCIe PHY serializer and deserializer - PCIe1_PHY_TX/PCIe1_PHY_RX. When PCIe_SS1 PIPE is configured to operate in dual-lane mode, it operates on two pairs of PCIe PHY serializer and deserializer - PCIe1_PHY_TX/PCIe1_PHY_RX and PCIe2_PHY_TX/PCIe2_PHY_RX, respectively. The single-lane PCIe_SS2 controller PIPE port (if enabled) can operate only on the PCIe2_PHY_TX/PCIe2_PHY_RX pair. Hereby, if PCIe_SS2 controller is used, the PCIe_SS1 can operate only in a single-lane mode on the PCIe1_PHY_TX/PCIe1_PHY_RX. In addition, PCIe PHY subsystem encompasses a PCIe PCS (physical coding sublayer), a PCIe power management logic, APLL, a DPLL reference clock generator and an APLL clock low-jitter buffer.

• The PCIe Controller implements the transport and link layers of the PCIe interface protocol.
• PCIe PCS (a physical coding sublayer component) converts a 8-bit portion of parallel data over a PCIe lane to a 10-bit parallel data to adapt the process of serialization and deserialization in the TX/RX PHYs to various requirements. At the same time it transforms the transmission rate to maintain the PCIe Gen2 bandwidth (5 Gbps) on both sides (PCIe controller and PHY).
• A multiplexer logic which adds flexibility to connect a PCIe controller hardware mapped PCS logic output to a single (for the single-lane PCIe_SS2 controller) or to a couple (for the 2-lane PCIe_SS1 controller) of PHY ports at a time
• Physical layer (PHY) serializer/deserializer components with associated power control logic, building the so called PMA (physical media attachment) part of the PCIe_PHY transceiver, as follows:
  • PCIe physical port 0 associated serializer (TX) - PCIe1_PHY_TX and deserializer (RX) - PCIe1_PHY_RX
  • PCIe physical port 1 associated serializer (TX) - PCIe2_PHY_TX and deserializer (RX) - PCIe2_PHY_RX
• DPLL_PCIe_REF is a DPLL clock source, controlled from the device PRCM, that provides a 100-MHz clock to the PCIe PHY serializer/deserializer components reference clock inputs.
• Both the PCIe_SS1 and PCIe_SS2 share the same APLL (APLLPCIe) which by default multiplies the DPLL_PCIe_REF (typically 100 MHz or 20 MHz) clock to 2.5 GHz.
• The APLLPCIe low-jitter buffer (ACSPCIE) and additional logic takes care to provide the PCIe APLL reference input clock.

PCIe module supports the following features:

• PCI Local Bus Specification revision 3.0
• PCI Express Base 3.0 Specification, revision 1.0.

At system level the device supports PCI express interface in the following configurations:

• Each PCIe subsystem controller has support for PCIe Gen2 mode (5.0 Gbps per lane) and Gen1 mode (2.5 Gbps per lane).
• One PCIe (PCIe_SS1) operates as Gen2 2-lanes supporting in either root-complex (RC) or end-point EP.
• Two PCIe (PCIe_SS1 and PCIe_SS2) operates Gen2 1-lane supporting either RC or EP with the possibility of one operating in Gen1 and one in Gen2.
• PCIe_SS1 can be configured to operate in either 2-Lane (dual lane) or 1-Lane (single lane) mode, as follows:
  • Single Lane - lane 0 mapped to the PCIe port 0 of the device
  • Flexible dual lane configuration - lanes 0 and 1 can be swapped on the two PCIe ports
• PCIe_SS2 can only operate in 1-Lane mode, as follows:
  • Single Lane - lane 0 mapped to the device PCIe port 1
  When PCie_SS1 is configured to operate in dual-lane mode, PCIe_SS2 is in-operable as both PCIe1_PHY_RX/TX and PCIe2_PHY_RX/TX are assigned to PCIe_SS1, and thereby NOT available to PCIe_SS2.

The main features of a device PCIe controller are:

• 16-bit operation at 250 MHz on PIPE interface (per 16-bit lane)
• One master port on the L3_MAIN supporting 32-bit address and 64-bit data bus.
• PCIe_SS1 master port dedicated MMU (device MMU2) on L3_MAIN path, to which PCIe traffic can be optionally mapped.
• One slave port on the L3_MAIN supporting 29-bit address and 64-bit data bus.
• Maximum outbound payload size of 64 Bytes (the L3 Interconnect PCIe1/2 target ports split bursts of size > 64 Bytes to the into multiple 64 Byte bursts)
• Maximum inbound payload size of 256 Bytes (internally converted to 128 Byte - bursts)
• No remote read request size limit: implicit support for 4 KiB-size and greater
• Support of EP legacy mode
• Support of inbound I/O accesses in EP legacy mode
• PIPE interface features fixed-width (16-bit data per lane) and dynamic frequency to switch between PCIe Gen1 and Gen2.
• Ultra-low transmit and receive latency
• Automatic Lane reversal as specified in the PCI Express Base 3.0 Specification, revision 1.0 (transmit and receive)
• Polarity inversion on receive
• Single Virtual Channel (VC0) and Single Traffic Class (TC0)
• Single Function in End point mode
• Automatic credit management
• ECRC generation and checking
• All PCI Device Power Management D-states with the exception of D3_cold/L2 state
• PCI Express Active State Power Management (ASPM) state L0s and L1 (with exceptions)
• PCI Express Link Power Management states except for L2 state
• PCI Express Advanced Error Reporting (AER)
• PCI Express messages for both transmit and receive
• Filtering for Posted, Non-Posted, and Completion traffic
• Configurable BAR filtering, I/O filtering, configuration filtering and completion lookup/timeout
• Access to configuration space registers and external application memory mapped registers through ECAM mechanism.
• Legacy PCI Interrupts reception (RC) and generation (EP)
• 2 x hardware interrupts per PCIe_SS1 and PCIe_SS2 controller mapped via the device Interrupt Crossbar (IRQ_CROSSBAR) to multiple device host (MPU, DSP, and so forth) interrupt controllers in the device
• MSIs generation and reception
• PCIe_PHY Loopback in RC mode

For more information, see section PCIe Controller in chapter Serial Communication Interfaces of the Device TRM.