A PTM Responder is permitted to issue PTM Response when it has stored copies of the historical timestamps (t3 - t2) but must request the PTM Master Time from elsewhere. In this case, it is permitted to issue PTM Response messages in response to PTM Request Messages while it retrieves the PTM Master Time if that retrieval is expected to take more than 10 μs. 这句话怎么理解

这句话是在讨论一个 PTM 响应器的行为。它的意思是，当 PTM 响应器存储了历史时间戳（t3 - t2）的副本时，可以在没有获得 PTM 主时间的情况下发出 PTM 响应。但是，如果检索 PTM 主时间需要超过 10 微秒，那么在检索 PTM 主时间的同时，该 PTM 响应器可以发出 PTM 响应消息以响应 PTM 请求消息。这意味着，如果 PTM 响应器需要从其他地方获取 PTM 主时间，而这个过程需要一定的时间，那么它可以在等待的同时回应 PTM 请求消息，以提高系统的响应速度。

相关问题

• Switch Downstream Ports and Root Ports acting as PTM Responders must respond to each PTM Request Message received at their Downstream Ports with either PTM Response or PTM ResponseD according to the following rules: ◦ A PTM Responder must not send a PTM Response or PTM ResponseD Message without first receiving a PTM Request Message. ◦ Upon receipt of a PTM Request Message, a PTM Responder must attempt to issue a PTM Response or PTM ResponseD Message within 10 μs. ◦ A PTM Responder must issue PTM Response when the Downstream Port does not have valid historical timestamps (t3 - t2) with which to fulfill a PTM Request Message. 翻译

• 作为 PTM Responders 的 Switch Downstream Ports 和 Root Ports 必须根据以下规则响应其收到的每个 PTM Request Message，使用 PTM Response 或 PTM ResponseD： ◦ PTM Responder 必须在先收到 PTM Request Message 后才能发送 PTM Response 或 PTM ResponseD Message。 ◦ 在收到 PTM Request Message 后，PTM Responder 必须在 10 微秒内尝试发出 PTM Response 或 PTM ResponseD Message。 ◦ 当 Downstream Port 没有有效的历史时间戳（t3 - t2）来满足 PTM Request Message 时，PTM Responder 必须发出 PTM Response。

Referring to Figure 6-24 , the following rules define timestamp capture: • A PTM Requester must update its stored t1 timestamp when transmitting a PTM Request Message, even if that transmission is a replay. • A PTM Responder must update its stored t2 timestamp when receiving a PTM Request Message, even if received TLP is a duplicate. • A PTM Responder must update its stored t3 timestamp when transmitting a PTM Response or ResponseD Message, even if that transmission is a replay. • A PTM Requester must update its stored t4 timestamp when receiving a PTM Response Message, even if received TLP is a duplicate. ◦ Timestamps must be based on the STP Symbol or Token that frames the TLP, as if observing the first bit of that Symbol or Token at the Port’s pins. Typically this will require an implementation specific adjustment to compensate for the inability to directly measure the time at the actual pins, as the time will commonly be measured at some internal point in the Rx or Tx path. The accuracy and consistency of this measurement are not bounded by this specification, but it is strongly recommended that the highest practical level of accuracy and consistency be achieved. 翻译一下

参考图6-24，以下规则定义了时间戳捕获：• PTM请求者在发送PTM请求消息时，必须更新其存储的t1时间戳，即使该传输是重播。• PTM响应者在接收PTM请求消息时，必须更新其存储的t2时间戳，即使接收到的TLP是重复的。• PTM响应者在传输PTM响应或ResponseD消息时，必须更新其存储的t3时间戳，即使该传输是重播。• PTM请求者在接收到PTM响应消息时，必须更新其存储的t4时间戳，即使接收到的TLP是重复的。◦ 时间戳必须基于框架TLP的STP符号或令牌，就好像在端口引脚上观察该符号或令牌的第一个比特位。通常，这将需要一种特定于实现的调整，以补偿无法直接测量实际引脚时间的能力，因为时间通常会在Rx或Tx路径中的某个内部点测量。此测量的准确性和一致性不受本规范的限制，但强烈建议实现最高实用级别的准确性和一致性。