Programming Model
18-26
ADSP-BF50x Blackfin Processor Hardware Reference
In transmit mode, as long as there is room in the SPI DMA FIFO
(the FIFO is not full), the SPI continues to request a DMA read
from memory. The DMA engine continues to read a word from
memory and write to the SPI DMA FIFO until the SPI DMA word
count register transitions from “1” to “0”. The SPI continues trans-
mitting words until the SPI DMA FIFO is empty.
See
Figure 18-9 on page 18-31
for additional information.
For receive DMA operations, if the DMA engine is unable to keep up with
the receive datastream, the receive buffer operates according to the state of
the
GM
bit in the
SPI_CTL
register. If
GM
= 1 and the DMA FIFO is full, the
device continues to receive new data from the
MISO
pin, overwriting the
older data in the
SPI_RDBR
register. If
GM
= 0, and the DMA FIFO is full,
the incoming data is discarded, and the
SPI_RDBR
register is not updated.
While performing receive DMA, the transmit buffer is assumed to be
empty (and
TXE
is set). If
SZ
= 1, the device repeatedly transmits zeros on
the
MOSI
pin. If
SZ
= 0, it repeatedly transmits the contents of the
SPI_TDBR
register. The
TXE
underrun condition cannot generate an error
interrupt in this mode.
For transmit DMA operations, the master SPI initiates a word transfer
only when there is data in the DMA FIFO. If the DMA FIFO is empty,
the SPI waits for the DMA engine to write to the DMA FIFO before start-
ing the transfer. All aspects of SPI receive operation should be ignored
when configured in transmit DMA mode, including the data in the
SPI_RDBR
register, and the status of the
RXS
and
RBSY
bits. The
RBSY
over-
run conditions cannot generate an error interrupt in this mode. The
TXE
underrun condition cannot happen in this mode (master DMA
TX
mode),
because the master SPI will not initiate a transfer if there is no data in the
DMA FIFO.
Writes to the
SPI_TDBR
register during an active SPI transmit DMA opera-
tion should not occur because the DMA data will be overwritten. Writes
Summary of Contents for EZ-KIT Lite ADSP-BF506F
Page 50: ...Contents l ADSP BF50x Blackfin Processor Hardware Reference ...
Page 92: ...Development Tools 1 30 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 110: ...Interface Overview 3 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 236: ...Internal Flash Memory Control Registers 6 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 650: ...Programming Examples 15 56 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 804: ...Programming Examples 17 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1194: ...Programming Examples 24 90 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1256: ...ACM Registers A 50 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1264: ...Boundary Scan Architecture B 8 ADSP BF50x Blackfin Processor Hardware Reference ...