Specific Boot Modes
16-50
ADSP-BF59x Blackfin Processor Hardware Reference
about the content of the boot stream. Further information regarding auto-
baud detection is given in
“Autobaud Detection” on page 11-13
.
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. When equipped with a
pull-up resistor the
HWAIT
signal imitates the behavior of an
UA0_RTS
out-
put 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.
Figure 16-18
shows 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 16-17. UART Autobaud Waveform
Figure 16-18. UART Boot - Host relying on HWAIT
UA0_TX
UA0_RX
0
0
0
1
1
1
RESET
HWAIT
1
0
0
1
0
0
0
0
0
0
1
1
1
UA0_TX
UA0_RX
0
0
1
1
RESET
HWAIT
0
0
0
0
0
1
1
1
1
Summary of Contents for ADSP-BF59x Blackfin
Page 64: ...Development Tools 1 22 ADSP BF59x Blackfin Processor Hardware Reference...
Page 74: ...Processor Specific MMRs 2 10 ADSP BF59x Blackfin Processor Hardware Reference...
Page 244: ...Programming Examples 6 40 ADSP BF59x Blackfin Processor Hardware Reference...
Page 700: ...Programming Examples 16 78 ADSP BF59x Blackfin Processor Hardware Reference...
Page 738: ...Boundary Scan Architecture B 8 ADSP BF59x Blackfin Processor Hardware Reference...