How endpoint 1 sends data without need for rootcomplex to forward the data
In a standard PCIe configuration, endpoint devices rely on the Root Complex for routing and forwarding data between different endpoints. However, in certain scenarios, it is possible for endpoint1 to communicate directly with endpoint2 without the involvement of the Root Complex. This can be achieved through PCIe Peer-to-Peer (P2P) communication or Non-Transparent Bridging (NTB). Let's look at these two approaches:
1. PCIe Peer-to-Peer (P2P) communication:
- P2P communication allows endpoints to communicate directly with each other without involving the Root Complex.
- Both endpoint1 and endpoint2 must support P2P transactions, and the specific capabilities and support can vary based on the hardware and PCIe specification version.
- To enable P2P communication, you typically need to enable P2P support in the device configuration registers of both endpoint1 and endpoint2.
- Once P2P support is enabled, endpoint1 can perform direct memory read or write transactions to the target address on endpoint2, bypassing the Root Complex.
2. Non-Transparent Bridging (NTB):
- NTB provides a mechanism for devices to directly communicate with each other through PCIe. It allows endpoint1 to appear as a bridge device to endpoint2.
- In NTB mode, endpoint1 acts as a bridge, forwarding transactions between other PCIe devices and endpoint2.
- NTB requires specific configuration on endpoint1, including setting up the bridge functionality and configuring the mapping of address ranges between endpoints.
- Once configured, endpoint1 can send data directly to endpoint2 without the need for the Root Complex to be involved.
Both P2P and NTB require specific support from the endpoints involved, and the implementation details can vary between hardware vendors and PCIe specification versions. It's crucial to consult the documentation provided by your hardware manufacturer to understand the P2P or NTB capabilities of your specific devices and how to configure them accordingly.
Additionally, support for P2P or NTB might require specific software drivers or firmware updates. Ensure that you have the necessary software components installed and up to date to enable these features.
I hope this clarifies how endpoint1 can send data directly to endpoint2 without the involvement of the Root Complex. If you have further questions or need more assistance, feel free to ask!