9
System Interface
9 – 3
CLKIN
CLKOUT
INTERNAL
PROCESSOR
STATE
1
2
3
4
4
PROCESSOR
CYCLE
1
2
3
4
PROCESSOR
CYCLE
Figure 9.3 Clock Signals & Processor States (ADSP-2171, ADSP-2181, ADSP-21msp58/59)
9.2.1
Synchronization Delay
Each processor has several asynchronous inputs (interrupt requests, for
example), which can be asserted in arbitrary phase to the processor clock.
The processor synchronizes such signals before recognizing them. The
delay associated with signal recognition is called synchronization delay.
Different asynchronous inputs are recognized at different points in the
processor cycle. Any asynchronous input must be valid prior to the
recognition point to be recognized in a particular cycle. If an input does
not meet the setup time on a given cycle, it is recognized either in the
current cycle or during the next cycle if it remains valid.
Edge-sensitive interrupt requests are latched internally so that the request
signal only has to meet the pulse width requirement. To ensure the
recognition of any asynchronous input, however, the input must be
asserted for at least one full processor cycle plus setup and hold time.
Setup and hold times are specified in the data sheet for each individual
device.
9.2.2
1x & 1/2x Clock Considerations
Each processor requires only a 1X or 1/2X frequency clock signal. They
use what is effectively an on-chip phase-locked loop to generate the higher
frequency internal clock signals and CLKOUT. Because these clocks are
generated based on the rising edge of CLKIN, there is no ambiguity about
the phase relationship of two processors sharing the same input clock.
Multiple processor synchronization is simplified as a result.