Propeller Manual

2: Spin Language Reference – CLKFREQ
Propeller Manual v1.1 · Page 63
CLKFREQ
Command: Current System Clock frequency; the frequency at which each cog is running.
((PUB ┆ PRI))
CLKFREQ
Returns: Current System Clock frequency, in Hz.
Explanation
The value returned by
CLKFREQ is the actual System Clock frequency as determined by the
current clock mode (oscillator type, gain, and PLL settings) and the external XI pin
frequency, if any. Objects use
CLKFREQ to determine the proper time delays for time-sensitive
operations. For example:
waitcnt(clkfreq / 10 + cnt) 'wait for .1 seconds (100 ms)
This statement divides CLKFREQ by 10 and adds the result to CNT (the current System Counter
value) then waits (
T
WAITCNTT) until the System Counter reaches the result value. Since CLKFREQ
is the number of cycles per second, a divide by 10 yields the number of clock cycles per 0.1
seconds, or 100 ms. So, disregarding the time it takes to process the expression, this
statement pauses the cog’s program execution for 100 ms. The table below shows more
examples of System Clock tick verses Time calculations.
Table 2-2: System Clock Ticks vs. Time Calculations
Expression Result
clkfreq / 10
Clock ticks per 0.1 seconds (100 ms)
clkfreq / 100
Clock ticks per 0.01 seconds (10 ms)
clkfreq / 1_000
Clock ticks per 0.001 seconds (1 ms)
clkfreq / 10_000
Clock ticks per 0.0001 seconds (100 µs)
clkfreq / 100_000
Clock ticks per 0.00001 seconds (10 µs)
clkfreq / 9600
Clock ticks per serial bit period at 9,600 baud (~ 104 µs)
clkfreq / 19200
Clock ticks per serial bit period at 19,200 baud (~ 52 µs)
The value that
CLKFREQ returns is actually read from long 0 (the first location in RAM) and
that value can change whenever the application changes the clock mode, either manually or
via the
CLKSET command. Objects that are time-sensitive should check CLKFREQ at strategic
points in order to adjust to new settings automatically.