MPC8544COMEDEV Freescale Semiconductor, MPC8544COMEDEV Datasheet - Page 905

• Manufacturer Part Number: MPC8544COMEDEV
• Description: KIT DEV EXPRESS MPC8544COM
• Manufacturer: Freescale Semiconductor
• Type: MPUr

Specifications of MPC8544COMEDEV

• Contents: Board
• For Use With/related Products: MPC8544
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

15.6.7
The eTSEC buffer descriptor (BD) is modeled after the MPC8260 Fast Ethernet controller BD for ease of
reuse across the PowerQUICC network processor family. Drawing from the MPC8260 FEC BD
programming model, the eTSEC descriptor base registers point to the beginning of BD rings. The eTSEC
BD also expands upon the MPC8260 BD model to accommodate the eTSEC’s unique features. However,
the 8-byte data BD format is designed to be compatible with the existing MPC8260 BD model.
15.6.7.1
Data buffers are used in the transmission and reception of Ethernet frames (see
encapsulate all information necessary for the eTSEC to transmit or receive an Ethernet frame. Within each
data BD there is a status field, a data length field, and a data pointer. The BD completely describes an
Ethernet packet by centralizing status information for the data packet in the status field of the BD and by
containing a data BD pointer to the location of the data buffer. Software is responsible for setting up the
BDs in memory. Because of pre-fetching, a minimum of four buffer descriptors per ring are required. This
applies to both the transmit and the receive descriptor rings. Transmit rings are limited to a maximum size
of 65536 BDs due to BD and frame data prefetching. Software also must have the data pointer pointing to
a legal memory location. Within the status field, there exists an ownership bit which defines the current
state of the buffer (pointed to by the data pointer). Other bits in the status field of the buffer descriptor are
used to communicate status/control information between the eTSEC and the software driver.
Because there is no next BD pointer in the transmit/receive BD (see
sequentially in memory. The eTSEC increments the current BD location appropriately to the next BD
location to be processed. There is a wrap bit in the last BD that informs the eTSEC to loop back to the
beginning of the BD chain. Software must initialize the TBASE and RBASE registers that point to the
beginning transmit and receive BDs for eTSEC.
Freescale Semiconductor
Buffer Descriptors
Data Buffer Descriptors
MPC8544E PowerQUICC III Integrated Host Processor Family Reference Manual, Rev. 1
Memory Map
RxBD Table
TxBD Table
(RBASE n )
(TBASE n )
Pointer
Pointer
Figure 15-133. Example of eTSEC Memory Structure for BDs
System Memory
Table for Ring n
Table for Ring n
Rx Buffer
Tx Buffer
RxBD
TxBD
Figure
Status & Control
Status & Control
Buffer Pointer
Buffer Pointer
Enhanced Three-Speed Ethernet Controllers
Data Length
Data Length
Tx Buffer Descriptors
Rx Buffer Descriptors
15-134), all BDs must reside
Figure
15-133). Data BDs
15-173