AXI (AMBA AXI) is designed for on-chip communication inside a System-on-Chip.
It connects components like:
• CPU
• DMA
• Memory controller
• On-chip peripherals
AXI uses a VALID/READY handshake mechanism and provides very low latency communication between IP blocks within the chip.
PCIe (Peripheral Component Interconnect Express) is designed for off-chip communication.
It connects the processor to external high-performance devices like:
• GPUs
• SSDs
• Network cards
• AI accelerators
PCIe is packet-based and uses a layered architecture:
• Transaction Layer
• Data Link Layer
• Physical Layer
Unlike AXI, PCIe includes CRC protection, ACK/NAK, replay buffers, and link training to ensure reliable communication across PCB traces.
Key Differences
AXI:
On-chip protocol
Parallel interface
VALID/READY flow control
Very low latency
PCIe:
Off-chip protocol
High-speed serial lanes
Credit-based flow control
CRC + retransmission support
In real SoCs, both protocols actually work together.
Typically, a PCIe controller connects to the internal AXI interconnect, acting as a bridge between the SoC and external devices.
CPU → AXI Interconnect → PCIe Controller → External Device