Semtech Corporation GN4124-CBE3

Overview

GN4124-CBE3 from Gennum is a 4-lane PCI Express to local bus bridge IC designed as an FPGA companion for high-performance native PCIe bridging in embedded and industrial systems. It integrates on-chip PCIe PHY, link, and transaction layers compliant with PCI Express Base Specification 1.1; supports dual virtual channels; delivers up to 800 MB/s bidirectional throughput via DDR SSTL local bus; and enables FPGA bitstream loading over PCIe.

For engineers reviewing the GN4124-CBE3 datasheet, pinout, applications, or equivalent options, key selection considerations include PCIe x4 lane compliance, DDR SSTL local bus timing (200 MHz DDR clock), dual VC support, on-the-fly FPGA configuration capability, and integrated MSI interrupt generation without external IP licensing.

Technical Context

The GN4124-CBE3 implements a hardwired PCI Express 1.1 stack-including physical, data link, and transaction layers-eliminating the need for licensed PCIe IP in FPGA-based designs. Its local bus interface uses source-synchronous DDR SSTL signaling (1.8 V) with separate SDR control clocks and DDR data clocks, enabling asynchronous operation relative to PCIe reference clocking.

It features a dedicated FPGA configuration loader supporting serial programming over PCIe, a 2-wire (I²C-compatible) controller for EEPROM boot and register access, and a flexible interrupt controller routing GPIO or internal sources to MSI or GPIO pins. Virtual channel arbitration uses independent on-chip buffering per VC to prevent blocking between traffic classes.

Key Specifications

Pinout & Package

GN4124-CBE3 is housed in a 256-pin PBGA package (17 mm × 17 mm, 1.0 mm pitch) with exposed thermal pad. Pin assignments are optimized for PCIe lane routing, DDR SSTL local bus signal integrity, and FPGA co-location.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PCIe-to-FPGA bridging applications.

Compared with Xilinx Virtex-5 FX70T, GN4124-CBE3 offloads PCIe protocol handling entirely, freeing FPGA resources for application logic and reducing power by ~300 mW; compared with PLX PEX8311, GN4124-CBE3 provides purpose-built DDR SSTL interface, dual VC arbitration, and PCIe-hosted FPGA configuration-enabling agile, low-footprint reconfigurable systems.

Availability

GN4124-CBE3 is available at Aetrix Electronics and suitable for medical imaging acquisition, industrial machine vision, test & measurement equipment, communications protocol analyzers, and FPGA-based accelerator cards requiring stable component supply and long-term industrial lifecycle support.

Supply support for GN4124-CBE3 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Gennum Corporation was a Canadian semiconductor company specializing in high-speed serial interface solutions, acquired by Microsemi in 2011. Its products targeted demanding embedded, broadcast, and industrial applications.

The GN4124-CBE3 belongs to Gennum's PCI Express Bridge Controller family, engineered specifically to enable cost-effective, low-power, FPGA-centric PCIe endpoint designs without requiring licensed protocol IP or complex FPGA resource allocation.

FAQ

Does GN4124-CBE3 support PCIe 2.0 or higher?

No, GN4124-CBE3 is compliant only with PCI Express Base Specification 1.1 (2.5 GT/s). It does not support PCIe 2.0 (5.0 GT/s) or later generations. The device's PHY, link, and transaction layers are fixed-function and not upgradeable via firmware or configuration. For PCIe 2.0+ requirements, alternative bridge solutions must be evaluated.

What is the role of the SPRI interface in GN4124-CBE3?

The Serial Programming Interface (SPRI) in GN4124-CBE3 enables PCIe-hosted FPGA configuration: the host CPU writes bitstream data to GN4124-CBE3's SPRI registers over BAR4, and GN4124-CBE3 serially clocks it out to the attached FPGA. This eliminates external PROM and supports on-the-fly reconfiguration-critical for field-upgradable GN4124-CBE3-based systems.

Can GN4124-CBE3 operate with a local bus clock slower than 200 MHz?

Yes, GN4124-CBE3 supports asynchronous local bus operation at frequencies below 200 MHz. The local bus clock (LCLK/LCLKn) may be scaled down to match FPGA logic requirements, reducing dynamic power consumption. Minimum supported rate is determined by setup/hold timing margins in the target FPGA I/O bank-not by GN4124-CBE3 itself.

How does GN4124-CBE3 handle PCIe link training with polarity inversion?

GN4124-CBE3 automatically detects and compensates for inverted polarity on PCIe receive lanes (PERp[3:0]/PERn[3:0]) during link training. This allows PCB layout flexibility-such as avoiding signal crossovers-without requiring manual lane swapping or strap configuration. The feature is implemented in the hardwired PHY and requires no user intervention or register programming in GN4124-CBE3.

Is GN4124-CBE3 pin-compatible with GN4121?

No, GN4124-CBE3 is not pin-compatible with GN4121. While both belong to the same Gennum family and share architectural similarities, GN4121 is a x1-lane PCIe bridge with different pin count, ball map, and I/O assignment. The GN4124-CBE3 uses a 256-ball PBGA package optimized for x4 lane routing and higher local bus bandwidth, whereas GN4121 uses a smaller package with reduced lane and I/O count.