Increase baud rate?

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steve220
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Joined: Tue Oct 11, 2016 2:32 pm

Increase baud rate?

Post by steve220 » Fri Sep 28, 2018 5:08 am

Is it possible to change the default baud rate of the V4 without doing a firmware recompile?
It is 115000 by default and I would like to change it to 250000.

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ednisley
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Re: Increase baud rate?

Post by ednisley » Fri Sep 28, 2018 12:50 pm

steve220 wrote:
Fri Sep 28, 2018 5:08 am
like to change it to 250000.
Depends on what hardware & software you're driving it with.

CH340 and genuine FTDI USB-to-serial chips don't do 250 kb/s and counterfeit FTDI chips are unstable at any speed.

Marlin's buffer isn't more than a few hundred bytes, tops, because Arduinos don't have much internal RAM. The yellow LED blinking inside the box shows the serial handshaking going on during data transfers: the serial buffer stays nearly full nearly all the time. As a result, the maximum printing speed doesn't depend on the maximum serial bit rate.

Other than bragging rights, what do you expect to achieve?

steve220
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Joined: Tue Oct 11, 2016 2:32 pm

Re: Increase baud rate?

Post by steve220 » Fri Sep 28, 2018 1:14 pm

Great question Ed,
There are a few threads regarding lower print quality using Octoprint VS printing from an SD card using the same gcode file. Here is one:
https://discourse.octoprint.org/t/poor- ... rd/3743/40

I am experiencing the same types of artifacts on roundish, organic models as discussed in the thread above.

There is some thought that on some types of models, the Pi’s used in Octoprint setups can't feed the gcode to the printers fast enough causing micro delays that result in lower quality. As a troubleshooting step, I was hoping to eliminate the baud rate as a factor.

steve220
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Joined: Tue Oct 11, 2016 2:32 pm

Re: Increase baud rate?

Post by steve220 » Fri Sep 28, 2018 1:19 pm

BTW, this is not my image, I copied it from the thread referenced above. The left print is printed from the SD card slot and the right is the same gcode printed from Octoprint. I'm seeing this same kind of effect on a small number of prints, typically those with a lot of round shapes and curves. I wonder if others are seeing these artifacts in the latest upgrades for octoprint?
A727E827-34ED-495B-A084-8BDE0A6A069D.jpeg

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ednisley
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Re: Increase baud rate?

Post by ednisley » Fri Sep 28, 2018 2:36 pm

steve220 wrote:
Fri Sep 28, 2018 1:14 pm
the Pi’s used in Octoprint setups can't feed the gcode to the printers fast enough
I'd be unsurprised, as the Pi's USB / network hardware leaves a lot to be desired. In fact, the network runs over the USB link inside the chip, so I'd expect watching the video camera would have more effect on the results.

In any event, doubling (or whatever) the raw speed will have absolutely no effect on the overall throughput, because the USB link sends the bits in bursty packets at a few megabits/second. It doesn't dribble them one at a time through an actual serial port.

It's possible an error in the Octoprint code (far from the USB handler) slows the overall data transfer, perhaps by introducing long pauses in the handshaking, but that's entirely separate from the raw serial data rate. The blobs look like very long pauses, indeed.
a lot of round shapes and curves
Everybody wants smoooooth curves, but those zillions of polygon faces don't buy you anything beyond G-Code bloat.

Cut the arc resolution to about 0.1 mm in the XY plane, watch the G-Code file shrivel, and you'll never see any difference in the actual plastic part.

It may be a workaround for the Pi's crappy hardware, but it's also a general rule of thumb: never use more polygons than you absolutely must.

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