Programming Model
15-24
ADSP-BF50x Blackfin Processor Hardware Reference
To reduce interrupt frequency on the receive side in non-DMA mode, the
ERFCI
status interrupt may be used as an alternative to the regular
ERBFI
receive interrupt. Hardware ensure that at least two (if
RFIT
=0) or four (if
RFIT
=1) words are available in the receive buffer by the time the interrupt
is requested.
DMA Mode
In this mode, separate receive (UARTxRX) and transmit (UARTxTX)
DMA channels move data between the UART and memory. The software
does not have to move data, it just has to set up the appropriate transfers
either through the descriptor mechanism or through autobuffer mode.
DMA channels provide a 4-deep FIFO, resulting in total buffer capabili-
ties of 6 words at the transmit and 9 words at the receive side receive sides.
In DMA mode, the latency is determined by the bus activity and arbitra-
tion mechanism and not by the processor loading and interrupt priorities.
For more information, see
“Direct Memory Access” on page 7-1
.
DMA interrupt routines must explicitly write 1s to the corresponding
DMAx_IRQ_STATUS
registers to clear the latched request of the pending
interrupt.
The UART’s DMA is enabled by first setting up the system DMA control
registers and then enabling the UART
ERBFI
and/or
ETBEI
interrupts in
the
UARTx_IER_SET
register. This is because the interrupt request lines
double as DMA request lines. Depending on whether DMA is enabled or
not, upon receiving these requests, the DMA control unit either generates
a direct memory access or passes the UART interrupt on to the system
interrupt handling unit. The UART’s status interrupt goes directly to the
system interrupt handling unit, bypassing the DMA unit completely.
For transmit DMA, it is recommended to set the
SYNC
bit in the
DMAx_
CONFIG
register. With this bit set, the interrupt generation is delayed until
the entire DMA FIFO is drained to the UART module. The UART TX
DMA interrupt service routine is allowed to disable the DMA or to clear
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 ...