Help, "PwmAddr" is "address of PWM variables in hub ram", please.
bteddy
Posts: 65
in Propeller 1
I found a piece of code and was reading thru it when I ran into something I didn't understand.
In the PUB section the parameters in the start call are pin, Freq and PwmAddr.
The code is commented stating that "PwmAddr" is "address of PWM variables in hub ram".
I could not find any reference to "PWM variables" in the forum.
Would someone explain this, or point me to documentation?
Thank You
In the PUB section the parameters in the start call are pin, Freq and PwmAddr.
The code is commented stating that "PwmAddr" is "address of PWM variables in hub ram".
I could not find any reference to "PWM variables" in the forum.
Would someone explain this, or point me to documentation?
Thank You
}}
VAR
long cog
PUB start(pin,Freq,PwmAddr) : okay | pmask
' pin number (first of two adjacent pins), frequency in Hz, address of PWM variables in hub ram
T_ := clkfreq/(Freq)
pin_ := pin
okay := cog := cognew(@entry, PwmAddr) + 1 ' Start cog
PUB getT ' This is the period of the PWM which is also the resolution, lower PWM frequencies give more resolution.
return T_
PUB stop
if cog
cogstop(cog~ - 1)
DAT
entry shl pmask_,pin_
or dira,pmask_ ' Set pins as outputs
mov pwmaddr1_,par ' Set up pointers to duty data
mov pwmaddr2_,pwmaddr1_
add pwmaddr2_,#4
mov t1, ctraval
add t1, pin_ ' set up counter A
mov frqa, #0
mov ctra, t1 ' nco mode on step pin
mov t1, ctrbval
add pin_, #1
add t1, pin_ ' set up counter B
mov frqb, #0
mov ctrb, t1 ' nco mode on step pin
mov frqa,#1
mov frqb,#1
mov time,cnt
add time,T_
' PWM loop
:loop {
Place other code here, as long as it takes less time than T_, roughly clkfreq/(4*(Freq)) instructions
That's about 2000 instructions at 10khz PWM frequency :)
}
rdlong duty1_,pwmaddr1_ ' Read duty1 from hub ram
rdlong duty2_,pwmaddr2_ ' Read duty2 from hub ram
waitcnt time, T_
neg phsa, duty1_
neg phsb, duty2_
jmp #:loop
time long 0
pmask_ long %11 ' Pin mask
pin_ long 0
duty1_ long 0
duty2_ long 0
T_ long 0 ' Time period
ctraval long %00100 << 26
ctrbval long %00100 << 26
t1 long 0
pwmaddr1_ long 0
pwmaddr2_ long 0
p long 0
Comments
instantiated more than once so its normal to pass in a pointer to working memory. I presume this memory
is live - ie can be written to to dynamically change the behaviour of the cog. Note the rdlong's into the duty1/2
variables.
The parameter would be @duty0 -- @ provides the run-time address of an object.
The code is taking advantage of the counters for dual PWM output. I've attached an object I wrote to do the same thing, though it may be easier to use because it's in Spin. Note, though, that using Spin to create the period timing for the desired frequency limits the upper end of the frequency to about 38kHz when running a standard 80MHz clock.
Unless you use fastspin, of course