Booting Process
19-20
ADSP-BF537 Blackfin Processor Hardware Reference
The signal polarity of the
HWAIT
strobe is programmable by an external
pull-up resistor in the 10 k
Ω
range. A pull-down resistor instructs the
HWAIT
signal to be active high. In this case the host is permitted to send
data when
HWAIT
is low, but should pause while
HWAIT
is high. This is the
mode used in SPI slave booting on other Blackfin derivatives. Similarly,
active-low behavior is programmed by a pull-up resistor.
After reset, the boot kernel waits to receive the first 10-byte block header.
At this time the
HWAIT
pin is not yet actively driven. Instead, the resistor
pulls the signal to the inactive state, encouraging the host to send data.
After receiving the ten bytes, the boot kernel knows whether to activate
the
HWAIT
signal and which GPIO to use. If
PPORT
is not zero, the boot
kernel first senses the polarity on the respective GPIO pin. Then, it
enables the output driver and inverts the signal polarity to immediately
hold off the host. The signal is not released again until the boot kernel is
ready for further data, or when a receive DMA has been started. As soon as
the DMA completes,
HWAIT
becomes active again.
Table 19-3. Settings for Port Function Enable and Muxing
Registers
BMODE
Boot Mode
PORTF_FER at boot time
PORT_MUX at
boot time
000
Bypass ROM, No-Boot
–
–
001
Parallel Flash on /AMS0
–
–
010
Reserved
PF1
–
011
SPI Memory
PF11, PF12, PF13, PF14
–
100
SPI Host
PF11, PF12, PF13, PF14
–
101
TWI Memory
–
–
110
TWI Host
–
–
111
UART Host
PF0, PF1
–
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 ...