Universal Serial Bus InterfaceMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 24-14924.12.1.3 DiscoveryIn a standard EHCI controller design, the EHCI host controller driver detects a Full speed (FS) or Lowspeed (LS) device by noting if the port enable bit is set after the port reset operation. The port enable willonly be set in a standard EHCI controller implementation after the port reset operation and when the hostand device negotiate a High-Speed connection (that is, Chirp completes successfully).The module will always set the port enable after the port reset operation regardless of the result of the hostdevice chirp result and the resulting port speed will be indicated by the PSPD field in PORTSCn.Therefore, the standard EHCI host controller driver requires an alteration to handle directly connected Fulland Low speed devices or hubs. The change is a fundamental one in that is summarized in Table 24-93.24.12.1.4 Data StructuresThe same data structures used for FS/LS transactions though a HS hub are also used for transactionsthrough the Root Hub. Here it is demonstrated how the Hub Address and Endpoint Speed fields should beset for directly attached FS/LS devices and hubs:1. QH (for direct attach FS/LS) – Async. (Bulk/Control Endpoints) Periodic (Interrupt)• Hub Address = 0• Transactions to direct attached device/hub.— QH.EPS = Port Speed• Transactions to a device downstream from direct attached FS hub.— QH.EPS = Downstream Device SpeedNOTEWhen QH.EPS = 01 (LS) and PORTSCn[PSPD] = 00 (FS), a LS-pre-pidwill be sent before the transmitting LS traffic.Maximum Packet Size must be less than or equal 64 or undefined behavior may result.2. siTD (for direct attach FS) – Periodic (ISO Endpoint)Table 24-93. Functional Differences Between EHCI and EHCI with Embedded TTStandard EHCI EHCI with Embedded Transaction TranslatorAfter port enable bit is set following a connectionand reset sequence, the device/hub is assumed tobe HS.After port enable bit is set following a connection and reset sequence, thedevice/hub speed is noted from PORTSCn.FS and LS devices are assumed to bedownstream from a HS hub thus, all port-levelcontrol is performed through the Hub Class to thenearest Hub.FS and LS device can be either downstream from a HS hub or directlyattached. When the FS/LS device is downstream from a HS hub, thenport-level control is done using the Hub Class through the nearest Hub.When a FS/LS device is directly attached, then port-level control isaccomplished using PORTSCn.FS and LS devices are assumed to bedownstream from a HS hub with HubAddr=X.[where HubAddr > 0 and HubAddr is the addressof the Hub where the bus transitions from HS toFS/LS (that is, Split target hub)]FS and LS device can be either downstream from a HS hub with HubAddr= X [HubAddr > 0] or directly attached [where HubAddr = 0 and HubAddris the address of the Root Hub where the bus transitions from HS to FS/LS(that is, Split target hub is the root hub)]
