Concepts

Concepts

Table of Contents

• Concepts

  • Table of Contents

  • CPLD “Complex Programmable Logic Device”

  • PCI – and Why It’s Called a “Link”?

    • That’s why people call it a link

CPLD “Complex Programmable Logic Device”

A CPLD is a small, reconfigurable hardware chip used on motherboards or server boards to control low-level logic (e.g., power sequencing, board-level signals).

What it actually does?

• When you update firmware on server hardware (e.g., BMC, BIOS, and CPLD), you’re updating different layers:

  • BIOS → Boot-time firmware configuring CPU, memory, PCIe, etc.

  • BMC → Baseboard Management Controller firmware providing remote management (IPMI/Redfish, power on/off, monitoring sensors).

  • CPLD → Hardware logic that controls things like:

    • Power routing and sequencing

    • Reset logic

    • Board signals that must react faster or more deterministically than software.

Note: CPLD code contains logic configuration like a simplified FPGA.

Note: Updating CPLD requires shutting down the target server to be updated first.

A Useful Analogy:

• BOIS: Operating System of the motherboard.

• BMC: Remote management supervisor.

• CPLD: Hardwired automation logic and traffic lights controlling signals.

PCI – and Why It’s Called a “Link”?

PCI (Peripheral Component Interconnect) is a communication bus standard that defines how components inside a computer exchange data with the CPU and memory.

• Originally PCI (parallel bus): Old and slower.

• Npw PCIe (PCI Express): high-speed serial links between device.

PCIe is a high-speed point-to-point data link, not just a slot

Instead of one shared bus, PCIe establishes point-to-point lanes, e.g:

• x1, x4, x8, x16 lanes: Each lane is full-duplex and independent.

• Lane counts is like how many parallel lines to transfer the series data.

That’s why people call it a link

• It’s literally a logical data link between two endpoints (CPU-GPU, CPU-NIC, etc).