Understanding PCIe Data Link Layer

1. Introduction PCI Express (PCIe) uses a layered architecture to separate concerns like transaction creation, reliability, and physical transmission. The Data Link Layer (DLL) ensures reliable communication between directly connected devices. The Transaction Layer generates packets (TLPs), and the Physical Layer transmits bits. The Data Link Layer sits between them, guaranteeing that TLPs are delivered correctly, in order, and without corruption over a single PCIe link. 2. PCIe Layers Transaction Layer (TL): Creates Transaction Layer Packets (TLPs) Data Link Layer (DLL): Ensures reliable delivery of TLPs Physical Layer (PHY): Handles signaling and bit transmission 3. Data Link Layer (DLL) 3.1 What Data Link Layer Does Responsibilities of DLL are: Reliable delivery: Sequence numbers + ACK/NAK + Replay buffer Error detection: LCRC (Link CRC) on every TLP Flow control: Credit based system to prevent buffer overflow DLL operates on two types of packets: TLPs (Transmission Layer Packets) -