NXP Semiconductors MCF5253, Reference Manual

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Universal Serial Bus Interface
MCF5253 Reference Manual, Rev. 1
Freescale Semiconductor 24-55
24.8.4.4 siTD Buffer Pointer List (Plus)
DWords 4 and 5 are the data buffer page pointers for the transfer. This structure supports one physical page
cross. The most significant 20 bits of each DWord in this section are the 4K (page) aligned buffer pointers.
The least significant 12 bits of each DWord are used as additional transfer state.
7–0 Status This field records the status of the transaction executed by the host controller for this slot. This field
is a bit vector with the following encoding:
Status Bit Definition
7 Active. Set by the software to enable the execution of an isochronous split
transaction by the Host Controller.
6 ERR. Set by the Host Controller when an ERR response is received from the
Companion Controller.
5 Data Buffer Error. Set by the Host Controller during status update to indicate that the
Host Controller is unable to keep up with the reception of incoming data (overrun) or
is unable to supply data fast enough during transmission (under run). In the case of
an under run, the Host Controller will transmit an incorrect CRC (thus invalidating the
data at the endpoint). If an overrun condition occurs, no action is necessary.
4 Babble Detected. Set by the Host Controller during status update when” babble” is
detected during the transaction generated by this descriptor.
3 Transaction Error (XactErr). Set by the Host Controller during status update in the
case where the host did not receive a valid response from the device (Time-out,
CRC, Bad PID, etc.). This bit will only be set for IN transactions.
2 Missed Micro-Frame. The host controller detected that a host-induced hold- off
caused the host controller to miss a required complete-split transaction.
1 Split Transaction State (SplitXstate). The bit encodings are:
0 Do Start Split. This value directs the host controller to issue a Start split
transaction to the endpoint when a match is encountered in the S-mask.
1 Do Complete Split. This value directs the host controller to issue a Complete split
transaction to the endpoint when a match is encountered in the C-mask.
0 Reserved. Bit reserved for future use and should be cleared.
Table 24-48. siTD Buffer Pointer Page 0 (Plus)
Bit Name Description
31–12 Buffer Pointer
(Page 0)
Bits [31–12] is a 4K page-aligned, physical memory addresses. These bits correspond to physical
address bits [31–12] respectively. The field P specifies the current active pointer
11–0 Current Offset The 12 least significant bits of the Page 0 pointer is the current byte offset for the current page
pointer (as selected with the page indicator bit (P field)). The host controller is not required to write
this field back when the siTD is retired (Active bit transitioned from a one to a zero).
Table 24-47. siTD Transfer Status and Control (continued)
Bit Name Description