Programming Model
13-18
ADSP-BF537 Blackfin Processor Hardware Reference
If another DMA is started while data is still pending in the UART trans-
mitter, there is no need to pulse the
ETBEI
bit to initiate the second DMA.
If, however, the recent byte has already been loaded into the
TSR
registers
(that is, the
THRE
bit is set), then the
ETBEI
bit must be cleared and set
again to let the second DMA start.
In DMA transmit mode, the
ETBEI
bit enables the peripheral request to
the DMA FIFO. The strobe on the memory side is still enabled by the
DMAEN
bit. If the DMA count is less than the DMA FIFO depth, which is
4, then the DMA interrupt might be requested already before the
ETBEI
bit is set. If this is not wanted, set the
SYNC
bit in the
DMAx_CONFIG
register.
L
Regardless of the
SYNC
setting, the DMA stream has not left the
UART transmitter completely at the time the interrupt is gener-
ated. Transmission may abort in the middle of the stream, causing
data loss, if the UART clock was disabled without additional poll-
ing of the
TEMT
bit.
The UART’s DMA supports 8-bit and 16-bit operation, but not 32-bit
operation. Sign extension is not supported.
Mixing Modes
Especially on the transmit side, switching from DMA mode to non-DMA
operation on the fly requires some thought. By default, the interrupt tim-
ing of the DMA is synchronized with the memory side of the DMA
FIFOs. The TX DMA completion interrupt is generated after the last byte
has been copied from the memory into the DMA FIFO. The TX DMA
interrupt service routine is not yet permitted to start other DMA
sequences or to switch to non-DMA transmission. The interrupt is
requested by the time the
DMA_DONE
bit is set. The
DMA_RUN
bit, however,
remains set until the data has completely left the TX DMA FIFO.
Therefore, when planning to switch from DMA to non-DMA of opera-
tion, always set the
SYNC
bit in the
DMAx_CONFIG
word of the last descriptor
or work unit before handing over control to non-DMA mode. Then, after
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...