Serial Peripheral Interface Controller
UG0331 User Guide Revision 15.0
516
14.2.2.6.3 Hardware Status Frame
A hardware status frame is automatically sent back by the SPE in response to every command. It
provides status information back to the master. The byte contains the contents of the
register.
14.2.2.6.4 Simple Commands
To send a command with no data to the slave, the master does the following:
1.
Sends a POLL command and verifies that the slave is ready (no RXBUSY from
register).
2.
This is repeated until the slave indicates it is ready.
3.
The master sends the other command with no data. The command is queued in the receive FIFO for
the slave to process.
14.2.2.6.5 Data Receive Operation
To send data to the slave, the master does the following:
1.
Sends a POLL command and verifies that the slave is ready and can accept the data.
2.
This is repeated until the slave indicates that it is ready and can accept the data (no RXBUSY from
register).
3.
The master sends the write command and data bytes. On receiving, the slave stores the command
and data bytes in the receive FIFO. After CMDSIZE bits have been received, the CMD interrupt is
generated.
4.
The hardware automatically set RxBUSY, if there are less than
storage locations left in the
receive FIFO after the sequence completes.
Note:
The slave reports under-run events having occurred, if no data is available for transmit.
14.2.2.6.6 Data Transmit Operation
To receive data from the slave, the master does the following:
1.
Sends a POLL command and verifies that the slave is ready and can accept the data.
2.
This is repeated until the slave indicates it is ready and can accept any associated command data
(no RxBUSY).
3.
The master sends a read command and any associated data bytes (for example, a read address).
On receiving the sequence, the slave stores the command byte and data in the receive FIFO. User
logic examines the command and data bytes and puts the requested data in the transmit FIFO. As
soon as it has written PKTSIZE bytes to the transmit FIFO, the TxBUSY status bit in the
register will be cleared.
4.
The master starts polling the device until the TxBUSY bit is cleared, indicating that the data is
available.
5.
The master now sends a read command followed by data words. The slave will return the contents
of the
register and required data words.
14.2.2.6.7 Under-Run in Slave Mode
Under normal operating conditions, the SPI slave core in slave mode has a transmit FIFO under-run
condition as the master initiates transfers when the slave transmit FIFO is empty (or attempts to transmit
data faster than the slave processor loads data).The core's operation can be modified by setting
register). Once set, the core will ignore the under-run conditions and simply
transmit zero frames when the transmit FIFO is empty at the start of a series of frames. If the first data
frame of a packet is read from the FIFO and transmitted, the under-run detection is enabled such that if
the transmit FIFO fails to provide any of the rest of the data packet (assuming SPI_X_SS[x] is active for
the whole packet), an over-run condition is signaled.
14.2.3
Initialization
This section describes the SPI initialization sequence, the SPI status at reset, and clock requirements.
The SPI can be initialized by configuring the SPI
register and the
system
registry.
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