ADSP-BF59x Blackfin Processor Hardware Reference
16-19
System Reset and Booting
The boot host wait signal holds the host from booting in any slave boot
mode and prevents it from being overrun with data. The
HWAIT
signal is,
however, available in all boot modes.
In general the host device must interrogate the
HWAIT
signal before every
word that is sent. This requirement can be relaxed for boot modes using
on-chip peripherals that feature larger receive FIFOs. However, the host
must not rely on the DMA FIFO since its content is cleared at the end of
a DMA work unit.
While the
HWAIT
signal is only used for boot purposes, it may also play a
significant role after booting. In slave boot modes, for example, the host
device does not necessarily know whether the Blackfin processor is in an
active mode or a power-down mode. For example, the
HWAIT
signal can be
used to signal when the processor is in hibernate mode.
Using HWAIT as Reset Indicator
While the
HWAIT
signal is mandatory in some boot modes, it is optional in
others.
If using a pull-up resistor, the
HWAIT
signal is driven low for the rest of the
boot process (and beyond). If using a pull-down resistor,
HWAIT
is driven
high.
With a pull-down resistor, this feature can be used to simulate an
active-low reset output. When the processor is reset, or in hibernate, the
GPIO is in a high impedance state and
HWAIT
is pulled low by the resistor.
As soon as the processor recovers and has settled the PLL again, the
HWAIT
is driven high and can alert external circuits.
Boot Termination
After the successful download of the application into the bootable mem-
ory, the boot kernel passes control to the user application. By default this
is performed by jumping to the vector stored in the
EVT1
register. The
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...