On Thu, 22 May 2014, JHC wrote: > Date: Thu, 22 May 2014 13:56:40 +0100 > From: JHC <gd-syst...@ntlworld.com> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: emc-users@lists.sourceforge.net > Subject: [Emc-users] Different PWM frequencies re HostMot2 pwmgen on 5i20 > > Hi all, > > Im setting up a machine with a Mesa 5i20 driving 3 DC servos via > homemade PWM/DIR amps. > I've got a couple of very nice ServoDisc DC servos (0-3000rpm within 60 > degrees of rotation!). I also want to get another I've seen with a 120:1 > harmonic drive for a future rotational axis. > > Question is this: > > To cut down on the ridiculous size of the output inductors I'll need for > the ServoDisc amps Id like to use at least 40khz PWM, but I've also got > an ESA 6F2 (3000rpm 120V 3.5Nm @9A - 17.5Nm @45A) which Id like to drive > using 2 of 3 half bridges from an integrated gatedriver IGBT module > which only goes up to 20khz PWM. > Can I have 40khz or more on 1 or 2 pwmgens and 20khz on another 2? > > I know bugger all about FPGAs, VHDL etc so making a custom firmware isnt > an option, just learning Linux and moving from TTL and PICs to power > electronics has opened up a big enough can of whoop ass on me for now. > > JHC
Its possible but not straighforward... All HostMot2 PWM channels share a common reference counter. The reference counter count rate is set by the PWM frequency parameter for all PWM generators. However each individual PWM generator has a resolution setting that allows selection of 9,10,11, or 12 bit PWM resolution. So for example you could set the PWM frequency to 20 KHz (the driver will then select 12 bit resolution for all PWM generators since it selects the best resolution it can achieve at the chosen PWM rate and 12 bits is possible at 20 KHz and the 5I20s 100 MHz clock-high rate) You could than use the raw-write facility in the driver to overwrite the PWM mode register for the 40 KHz channels to select 11 bit resolution instead. This will double the output frequency (you could use up to 8X (160 KHz) if needed by chosing 9 bits resolution) Once this is done you would have to restrict the PWM setting of the high frequency channels in HAL to 1/2 their normal range or the PWM woud "wrap" since the driver doesn't know that the PWM resolution has changed. This can be done by setting the PID comps max output parameter. Here is the (per channel) register that needs to be changed: (from the regmap file) PWM mode registers 6 bits Bit 1,0 = width select (With FPGA compile time constant PWM width = 13) 00 = 9 bit PWM 01 = 10 bit PWM 10 = 11 bit PWM 11 = 12 bit PWM Bit 2 = PWM mode select 0 = Straight (Sawtooth) PWM 1 = Symmetrical (Triangle) PWM Bit 4,3 = PWM output mode select 00 = Normal Sign Magnitude PWM&DIR outputs normal 01 = Normal Sign Magnitude PWM&DIR outputs swapped (for locked antiphase) 10 = Up/down mode 11 = PDM mode (12 bits) Bit 5 = Double Buffered mode When bit 5 is set, the PWMval register is not updated until the beginning of a PWM cycle, avoiding extra transitions in the output PWM waveform. This adds an extra delay of 0 to PWMWidth/PWMClock (normal mode) or PWMWidth*2/PWMClock (Symmetrical mode) between when the host writes the PWMVal register and the PWM output is updated. This mode should be used with HBridges. These registers are at 0x410X in the FPGA memory space (X= 0,4,8, etc for PWM 0,1,2 etc) so to set the PWM resolution to 11, you would write 0x00000022 to 0x410X (11 bit resolution and buffered mode) This can be done with raw-write in hal: setp hm2_5i20.0.raw.write_address 0x4100 setp hm2_5i20.0.raw.write_data 0x00000022 setp hm2_5i20.0.raw.write_strobe true (and duplicated for the other channels that need 2x PWM rates) > > ------------------------------------------------------------------------------ > "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE > Instantly run your Selenium tests across 300+ browser/OS combos. > Get unparalleled scalability from the best Selenium testing platform available > Simple to use. Nothing to install. Get started now for free." > http://p.sf.net/sfu/SauceLabs > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
