Serial Peripheral Interface (SPI)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
30-12
Freescale Semiconductor
30.6
SPI Commands
Table 30-7
lists transmit/receive commands sent to the CPM command register (CPCR).
30.7
The SPI Buffer Descriptor (BD) Table
As shown in
Figure 30-10
, buffer descriptors (BDs) are organized into separate Rx and Tx BD tables in
dual-port RAM. The tables have the same basic configuration as the SCCs and SMCs and form circular
queues that determine the order buffers are transferred. The CPM 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 30-10. SPI Memory Structure
30.7.1
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 30-11
and
Figure 30-12
, has the following
structure:
•
The half word at 0 contains status and control bits. The CPM updates the status bits after
the buffer is sent or received.
Table 30-7. SPI Commands
Command
Description
INIT
TX
PARAMETERS
Initializes all transmit parameters in the parameter RAM to their reset state and should be issued
only when the transmitter is disabled. The
INIT
TX
AND
RX
PARAMETERS
command can also be used
to reset both the Tx and Rx parameters.
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.
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
Summary of Contents for PowerQUICC MPC870
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