Information

Universal Serial Bus Interface
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
13-126 Freescale Semiconductor
13.7.1.2 Transfer Overlay
The seven DWords in the overlay area represent a transaction working space for the device controller. The
general operational model is that the device controller can detect whether the overlay area contains a
description of an active transfer. If it does not contain an active transfer, then it will not read the associated
endpoint.
After an endpoint is readied, the dTD is copied into this queue head overlay area by the device controller.
Until a transfer is expired, software must not write the queue head overlay area or the associated transfer
descriptor. When the transfer is complete, the device controller will write the results back to the original
transfer descriptor and advance the queue.
See dTD for a description of the overlay fields.
13.7.1.3 Current dTD Pointer
The current dTD pointer is used by the device controller to locate the transfer in progress. This word is for
USB_DR (hardware) use only and should not be modified by DCD software.
Table 13-76 describes the current dTD pointer fields.
13.7.1.4 Setup Buffer
The setup buffer is dedicated storage for the 8-byte data that follows a setup PID.
NOTE
Each endpoint has a TX and an RX dQH associated with it, and only the RX
queue head is used for receiving setup data packets.
28–27 — Reserved, should be cleared. These bit reserved for future use and should be cleared.
26–16 Maximum
Packet
Length
Maximum packet length. This directly corresponds to the maximum packet size of the associated endpoint
(wMaxPacketSize). The maximum value this field may contain is 0x400 (1024).
15 ios Interrupt on setup (IOS). This bit is used on control type endpoints to indicate if USBINT is set in response
to a setup being received.
14–0 Reserved, should be cleared. Bits reserved for future use and should be cleared.
Table 13-76. Current dTD Pointer
Bits Description
31–5 Current dtd. This field is a pointer to the dTD that is represented in the transfer overlay area. This field is modified by
the Device Controller to next dTD pointer during endpoint priming or queue advance.
4–0 Reserved, should be cleared. Bit reserved for future use and should be cleared.
Table 13-75. Endpoint Capabilities/Characteristics (continued)
Bits Name Description