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Type-C R1.2 Note（三）
接Note（二）， SRC与SNK的CC model类似，DRP的model如下图：
1、DRP使用FET打开/关闭 VBUS，初始状态下VBUS关闭；
2、DRP使用switch实现SRC/SNK状态切换；
3、SRC/SNK的toggle逻辑：进入某一稳定状态之前，DRP可以在SRC/SNK之间alternate；时间为tDRP； 当DRP作为SRC时， 会进行如检测SNK、打开VBUS、VCONN，且持续时间至少为tDRPhold； 当作为SNK时，检测VBUS；
4、支持Advanced function时，使用PD协议；
Power Role & Role Swawpping
七种基本Power Role: SRC(only),SNK(only), SRC(default), SNK(default),DRP(toggling)，DRP(SRCING device)，DRP(SNKING host)
两种转换机制： 第一是Role初始化时； 第二是PD协议；
第一种基本上可以概括为：DRP可能以TRY.SRC或（和）TRY.SNK来swap role，导致role初始化结果的变化； 但是 TRY.SRC或（和）TRY.SNK都只能使用一次。。
第二种PD： PD协议可能有PR_swap, DR_swap, VCONN_swap;
• The PR_Swap command changes the port’s power state as reflected in the following state machines. PR_Swap does not change the port sourcing VCONN.
• The DR_Swap command has no effect on the following state machines or VCONN as it only changes the port’s data role.
• VCONN_Swap command changes the port sourcing VCONN. The PR_Swap command and DR_Swap command have no effect on the port sourcing VCONN.
CC functional & behavioral requirements
描述了各种不同状态之间的转换过程，及各个状态本身的定义。 每个状态转换到其他状态都有一定的要求。
USB port interoperability behavior
SRC to SNK:
1、 SRC、SNK都处于初始unattached 状态；
2、SRC 从Unattached.SRC to Attached.SRC through AttachWait.SRC by：
SRC 通过检测CC下拉电阻，来检测SNK连接； 进而打开VBUS和VCONN；
3、SNK从Unattached.SNK to Attached.SNK through AttachWait.SNK by：检测VBUS
注：Sink may skip AttachWait.SNK if it is USB 2.0 only and does not support accessories.
4、当SRC和SNK都处于attached状态时：
SRC通过调节Rp来限制流到SNK的电流值；SNK监控vRd以获得合适的VBUS； SRC和SNK都实时检测彼此是否连接；
SRC to DRP、DRP to SNK的机制类似，需要重点描述一下DRP to DRP，因为这里存在Role swapping的可能性：通过TRY.SRC或TRY.SNK；
分为三种情况： case1，case2，case3；
case1： Random result；
Copyright © 2016 USB 3.0 Promoter Group. All rights reserved.
Figure 4-22 illustrates the functional model for a DRP connected to a DRP in the first case described. The single CC wire that is in a standard cable is only shown in one of the four possible connection routes, CC1 to CC1. Port numbers have been arbitrarily assigned in the diagram to assist the reader to understand the process description.
Figure 4-22 DRP to DRP Functional Model – CASE 1
CASE 1: The following describes the behavior when a DRP is connected to another DRP. In this flow, the two DRPs accept the resulting Source-to-Sink relationship achieved randomly.
CASE 2: The following describes the behavior when a DRP is connected to another DRP. In this flow, the DRP #2 chooses to drive the random result to the opposite result using the Try.SRC mechanism.
CASE 3: The following describes the behavior when a DRP is connected to another DRP. In this flow, the DRP #1 chooses to drive the random result to the opposite result using the Try.SNK mechanism.
SRC to SRC、SNK to SNK，都以进入unattached状态结束。
POWER：
优先级PD>USB C current>BC1.2>Default;
For example, once the PD mode (e.g. a power contract has been negotiated) has been entered, the device shall abide by that power contract ignoring any other previously made or offered by the USB Type C Current, USB BC 1.2 or USB 2.0 and USB 3.1 spec. When the PD mode is exited, the device shall fallback in order to the USB Type C Current, USB BC 1.2 or USB 2.0 and USB 3.1 spec. power levels.
All USB Typ C ports shall tolerate being connected to USB power source supplying default USB power, e.g. a host being connected to a legacy USB charger that always supplies VBUS.
POWER during suspend:
USB 2.0 &3.1 spec. 定义了SNK在suspend状态时可以consume的电流值；
USB Suspend状态 aplied when：USB TPYE-C CURRENT is at default level 或 PD with suspend bit set properly；
When USB Type C Current is set at 1.5 A or 3.0 A, the Sink is allowed to continue to draw current from VBUS during USB suspend. During USB suspend, the Sink’s requirement to track and meet the USB Type C Current advertisement remains in force (See Section 4.5.2.3).
USB PD provides a method for the Source to communicate to the Sink whether or not the Sink has to follow the USB power rules for suspend.
VBUS req. during suspend： 当SRC在suspend状态下提供VBUS，同时该SRC应该提供至少7.5mA给VCONN；
E-Marked cable 从VCONN 获取电流不能大于7.5mA during suspend；
Vconn req. during suspend：
