What is Clkreq in PCIe?

That is done by adding additional functionality to an existing PCIe pin (CLKREQ#) to provide a very simple signaling protocol. This allows the PCIe transceivers to turn off their high-speed circuits and rely on the new signaling to wake them up again. 2 even allows turning off the common mode keeper circuits.

What is PCI generation?

The Peripheral Component Interconnect Express (PCI Express or PCIe) is a high-speed interface standard for connecting additional graphics cards (GPUs), Local Area Network (LAN) ports, NVME solid-state drives (SSDs), Universal Serial Bus (USB) ports and other hardware to a computer’s motherboard.

What is Perst in PCIe?

> The PERST# signal is used to indicate when the power supply is within its specified voltage tolerance and is stable. It also initializes a component’s state machines and other logic once power supplies stabilize.

What is PCI Express power management?

Active-state power management (ASPM) is a power management mechanism for PCI Express devices to garner power savings while otherwise in a fully active state. This is known as ASPM exit latency and takes up valuable time which can be annoying to the end user if it is too obvious when it occurs.

How is the Perst delay circuit connected to the clkreq?

It will simply connected to the CLKREQ# delay circuit, which, allowing you to choose how many seconds you want before it lower the wire to ground. However, for PERST#, it connects the motherboard, the GPU and the PERST# delay circuit all together.

How are Perst and clkreq related to each other?

Basically they are related to how a motherboard initialize a device. Per https://pcisig.com/sites/default/files/specification_documents/MiniEx_M2_ECR_PERST_CLKREQ_Power-up-Reqts_20140918_Final.pdf, we can learned that for a normal motherboard + pcie device, when you press the power button the 3.3V power is firstly established.

How is the clkreq connected to the GPU?

For PE4c semantics ( http://www.bplus.com.tw/PDF/PE4C_V30_20150129A.pdf ), the CLKREQ# is not connected to the GPU at all. It will simply connected to the CLKREQ# delay circuit, which, allowing you to choose how many seconds you want before it lower the wire to ground.

What happens when the motherboard detects a clkreq?

When the motherboard detects a CLKREQ, it will try to establish the reference clock, then issue PERST# by raise it to 3.3V to let the device know it. After that the device will pick the reference clock and start communicating with the motherboard.