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Forum Index : Microcontroller and PC projects : PWM enhancements in 5.07.06 (undocumented)
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| matherp Guru  Joined: 11/12/2012 Location: United KingdomPosts: 10315 |
The 5.07.06 release notes and manual document the ability to optionally invert the PWM channels but that was actually part of a much more powerful change to PWM that is included in 5.07.06 (get the very latest download from Geoff's site). This change is difficult to document and late breaking hence the omission in the current manual. The PWM command is modified as follows: PWM channel, frequency, [dutyA] [,dutyB] [,deferredstart] The new parameter "deferredstart" when set to 1 prepares the PWM channels as before but does not start the output running. This is to avoid any undesirable startup artefacts There is a new sub command PWM SYNC [channel0offset] [,channel1offset] .......[channel7offset] This initiates the PWM on channels where a deferred start was defined or just syncs exisitng running channels. However, the power comes in the ability to offset the channels one to another (defined as a percentage of the time period as per the duty cycle - can be a float) In this thread a method is described to create two signals with one starting after the other and ending before it. With the new functionality this is easy without pokes or changing frequency. setpin GP0,PWM setpin GP2,PWM PWM 0,10000,50,,1 PWM 1,10000,40,,1 PWM SYNC 0,5  The same method can create a quadrature clock setpin GP0,PWM setpin GP2,PWM setpin GP4,PWM setpin GP6,PWM PWM 0,10000,25,,1 PWM 1,10000,25,,1 PWM 2,10000,25,,1 PWM 3,10000,25,,1 PWM SYNC 0,25,50,75 Unfortunately I don't have a 4 channel scope  The SYNC command can also be used when the channels are already running e.g. setpin GP0,PWM setpin GP2,PWM PWM 0,10000,50 PWM 1,10000,50 do for i=0 to 99 PWM SYNC 0,i pause 50 next loop Edited 2023-01-09 18:46 by matherp |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5091 |
Hi Peter, This works (only) on different PWM's. So you could potentially also use it to generate fading in game sounds. One PWM at 1kHz, the other at 998Hz. And use sync to start them simultaneous. And PWM STOP to stop them. Martin may like this, he has some game sounds that take a lot of CPU power, much simpler this way. Nice feature... Volhout P.S. In my particular switchmode power supply test, I used 100kHz up to 400kHz frequencies, and had very small time offsets. That would require fractions of a microsecond start delay. I guess in that application the "poke" still is needed. PicomiteVGA PETSCII ROBOTS |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10315 |
In the margin you are limited by the number of clock pulses in the time period @400KHz with 1CPU @ 378MHz you have 945 clock periods per cycle so half of that is 472 and therefore a "shorter" pulse must be 470. Either method hits exactly the same limitation. setpin gp0,pwm setpin gp2,pwm pwm 0,400000,50,,1 pwm 1,400000,49.8,,1 pwm sync 0,0.1 pw gives you a symmetrical pair of pulses with exactly 1 count offset (2.6ns) at each end when the CPU clock is 378MHz. |
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disco4now Guru Joined: 18/12/2014 Location: AustraliaPosts: 1003 |
Hi Peter, Can the duty cycle be changed while the PWMs are running and keep the same phase relationship.i.e is this valid setpin GP0,PWM setpin GP2,PWM setpin GP4,PWM setpin GP6,PWM PWM 0,10000,25,,1 PWM 1,10000,25,,1 PWM 2,10000,25,,1 PWM 3,10000,25,,1 PWM SYNC 0,25,50,75 for x=25 to 50 step 5 PWM 0,10000,x PWM 1,10000,x PWM 2,10000,x PWM 3,10000,x pause 100 next x Latest F4 Latest H7 FotS |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10315 |
yes Forgot to mention you can use an offset of -1 to omit a channel from the synch e.g. setpin gp0,pwm setpin gp1,pwm pwm 0,5000,33,66 setpin gp2,pwm setpin gp4,pwm pwm 1,10000,25,,1 pwm 2,10000,25 pwm sync -1,0,25 ' syncs channels 1 and 2 but leaves 0 untouched Edited 2023-01-10 01:47 by matherp |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
It would be nice if the same thing could be done for PLAY TONE... Jim VK7JH MMedit |
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karlelch Senior Member  Joined: 30/10/2014 Location: GermanyPosts: 237 |
This option to offset PWM channel starts may also be useful when starting multiple servos at once - that is, to spread to initial current draw over some small time window. Thomas |
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