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Writing SD Card via USB

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I think the Marlin firmware may support it, I'm not sure. I know Repetier firmware does.

But in practice it's a huge pain. The USB connection on Arduino devices generally (never?) run in full-speed USB compatibility mode. Instead it runs in a generic dumbed-down serial link mode, which limits the speed to at best 250000 baud.

One of the reasons to use SD cards instead of the USB link for printing stuff is because the USB link can be too slow to keep up with how fast the printer can print, whereas the bandwidth reading the SD is much higher, and it can (usually) keep the printer fed with commands.

In other words, transferring a gcode file over USB can take longer than it would take to print the file. Probably a bit faster for most prints, but probably same order of magnitude. A file that a computer can write directly to a card in a few seconds (at full card/USB speed) can take many many minutes over USB to the printer.

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To add on the info from Illuminarti. I've done some test with this a year ago, with the USB transfer speeds that we have, it's not worth it. It can take anything from 20 minutes to an hour to transfer a gcode file.


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The firmware is only a few kilobytes in size (The one I've built recently was 288 kB). It's just as slow as anything else, but less data = less time. A Gcode file can be several Megabytes (biggest one I've had so far was 20 MB -> The Colonel from Thingiverse).

We are intending to do just about the same thing in a few weeks but we're using a Cortex M3 MCU which is a little bit faster than the Arduino - didn't take that into account before...


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