PCIE ASPM L0, L0s, L1, L2, L3

工作上常常會被要求check這個，但究竟他們的關係是什麼，今天才了解。
或許在評估battery life的時候會有幫助。自己的經驗，L1的功能比L0s還要大得多了。
詳細的還是參考spec。
L0 – All PCI Express transactions and other operations are enabled.
L0s – A low resume latency, energy saving “standby” state.
L1 – Higher latency, lower power “standby” state.  (optional)
L2/L3 Ready – Staging point for L2 or L3
L2 – Auxiliary powered Link deep energy saving state.
L3 – Link Off state.
Zero power state.
LDn – A transitional Link Down pseudo-state prior to L0