ADSP-BF50x Blackfin Processor Hardware Reference
24-57
System Reset and Booting
When the boot kernel is processing fill or initcode blocks it might require
extra processing time and needs to hold the host off from sending more
data. This is signalled with the
HWAIT
output as well as by the
RTS
output.
When equipped with a pull-up resistor the
HWAIT
signal imitates the
behavior of an
UA0_RTS
output and could be connected to the
CTS
input of
the booting host. The host is not allowed to send data until
HWAIT
turns
inactive after a reset cycle. Therefore a pulling resistor on the
HWAIT
signal
is required.
If the resistor pulls to ground, the host must pause transmission when
HWAIT
is low and is permitted to send when
HWAIT
is high. A pull-up resis-
tor inverts the signal polarity of
HWAIT
. The host should test
HWAIT
at every
transmitted byte.
During ADSP-BF50x boot operation, the host device more likely relies on
the
RTS
output of UART0. Then, the use of
HWAIT
becomes optional. At
boot time the Blackfin processor does not evaluate
RTS
signals driven by
the host and the UART0
UA0_CTS
input is inactive. Since the
UA0_RTS
is in
a high impedance state when the Blackfin processor is in reset or while
executing preboot, an external pull-up resistor to
V
DDEXT
is recommended.
Figure 24-19
and
Figure 24-20
show the initial case of the UART boot
mode. As soon as
HWAIT
releases after reset, the boot kernel expects to
receive a 0x40 byte for bit rate detection. After the bit rate is known, the
UART is enabled and the kernel transmits for bytes.
Figure 24-19
and
Figure 24-20
compare
UA0_RTS
and
HWAIT
timing when
an extended initcode executes. Since code execution distracts from data
loading, the host device should be prevented from sending more data. The
HWAIT
timing is much more conservative than the
RTS
. If the host relies on
HWAIT
, the UART receive buffer may not be filled over watermark level
and
UA0_RTS
might not be deasserted at all. If, however, the host relies on
UA0_RTS
, it will be stalled a couple of bytes later. Both methods are valid.
Содержание EZ-KIT Lite ADSP-BF506F
Страница 50: ...Contents l ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 92: ...Development Tools 1 30 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 110: ...Interface Overview 3 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 132: ...Unique Information for the ADSP BF50x Processor 4 22 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 236: ...Internal Flash Memory Control Registers 6 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 342: ...Unique Information for the ADSP BF50x Processor 7 106 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 484: ...Unique Information for the ADSP BF50x Processor 10 60 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 493: ...ADSP BF50x Blackfin Processor Hardware Reference 11 9 Core Timer Unique Information for the ADSP BF50x Processor None ...
Страница 494: ...Unique Information for the ADSP BF50x Processor 11 10 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 506: ...Unique Information for the ADSP BF50x Processor 12 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 544: ...Unique Information for the ADSP BF50x Processor 13 38 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 650: ...Programming Examples 15 56 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 712: ...Unique Information for the ADSP BF50x Processor 16 62 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 804: ...Programming Examples 17 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 972: ...Unique Information for the ADSP BF50x Processor 20 38 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 1194: ...Programming Examples 24 90 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 1256: ...ACM Registers A 50 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 1264: ...Boundary Scan Architecture B 8 ADSP BF50x Blackfin Processor Hardware Reference ...