Freescale Semiconductor MPC8260 - Manual (Page 1259)

Serial Peripheral Interface (SPI)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 38-13
38.7 The SPI Buffer Descriptor (BD) Table
As shown in Figure 38-10 , BDs are organized into separate RxBD and TxBD tables in dual-port RAM.
The tables have the same basic configuration as for the SCCs and SMCs and form circular queues that
determine the order buffers are transferred. The CP uses BDs to confirm reception and transmission or to
indicate error conditions so that the core knows buffers have been serviced. The buffers themselves can be
placed in external memory or in any unused parameter area of the dual-port RAM.
Figure 38-10. SPI Memory Structure
38.7.1 SPI Buffer Descriptors (BDs)
Receive and transmit BDs report information about each buffer transferred and whether a maskable
interrupt should be generated. Each 64-bit BD, shown in
Figure 38-11 and Figure 38-12 , has the following
structure:
• The half word at offset + 0 contains status and control bits. The CP updates the status bits after the
buffer is sent or received.
• The half word at offset + 2 contains the data length (in bytes) that is sent or received.
— For an RxBD, this is the number of octets the CP writes into this RxBD’s buffer once the BD
closes. The CP updates this field after the received data is placed into the buffer. Memory
allocated for this buffer should be no smaller than MRBLR.
CLOSE RXBD Forces the SPI controller to close the current RxBD and use the next BD for subsequently received
data. If the controller is not receiving data, no action is taken. Use this command to extract data from
a partially full buffer.
INIT RX
PARAMETERS
Initializes all receive parameters in the parameter RAM to their reset state. Should be issued only
when the receiver is disabled. The
INIT TX AND RX PARAMETERS command can also be used to reset
both the Tx and Rx parameters.
Table 38-7. SPI Commands (continued)
Command Description
Frame Status
Data Length
Buffer Pointer
Frame Status
Data Length
Buffer Pointer
Tx Buffer
Pointer to SPI
RxBD Table
Rx Buffer
Dual-Port RAM External Memory
TxBD Table
RxBD Table
Tx Buffer
Pointer to SPI
TxBD Table