For the cable you can use your wand swd cable. Should work.
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You can do both technically, it’s a ‘bare-metal’ interface that allows you to write the entire flash of the MCU without using USB (which is a device that the MCU has to host). Generally you flash the bootloader with SWD, which then allows you to load a program on it over USB, but I believe the vesc-tool scripts these together.
And to expand: The bootloader is a little program that executes at startup and allows the USB programming function to work + starts the program running on the MCU.
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Great explanation, thanks! 
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is there a version history or changelogs for the bootloader? can an esc running a bootloader that was applied by a 2.x or ack bldc/vesc-tool app be programmed with firmware 4.x?
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Based on the reports I’ve seen with this 4.0+ release, it looks like there are varying degrees of success on this.
5 mentions of bootloader in the ChangeLog but not a ton of specifics:
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Fingers crossed for OpenRoad…
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You can upload the FW, using the old bootloader. If the FW changes, the bootloader worked just fine, if the FW does not upload there is no bootloader on the ESC and you can load the missing bootloader.
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That is correct.
hi frank, thank you so much for your reply
is compressed firmware transfer a feature that is built into the bootloader? that is to say, is it possible that i could use the latest vesc-tool with the intention of applying the latest 4.x firmware, but if the bootloader on my ESC is too old i would have to patiently wait for the firmware to be transferred uncompressed?
i’m glad that esc’s running old bootloaders can accept the latest firmware. is the reverse also true? once i apply the latest bootloader to an ESC, should i anticipate any issues trying to apply an old firmware?
I just had a longer conversation about the wobble that can happen due to the Time Constant.
Benjamin is fixing the issue right now.
The good news: We will probably use this matter to find a way to detect wobbles in future, so that the VESC can work against speed wobbles and stabilize the rear truck, using both motors to create a counter oscillation.
The other thing that will become available in one of the next updates is button to go back to the old setup.
Basically the entire device software and config will be saved prior to the FW update, so that a single click will bring you back to your old setup and config. Like in any software, you can press that BACK button and you are back to what you had before.
We will advise users to keep an existing setup and config if it worked good for you in the past.
You can then try out the latest FW and see if that works even better for you, or enjoy/try new features, but you can also just go back and use your stable setup again.
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Why hasn’t anyone thought of this before? That’s a great idea.
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At least we want to get something positive from this and since motors can react very fast to an occurrence, it is possible. Benjamin Vedder likes to nail problems that pop up and can be solved. We will try to solve speed whobble.
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Any discussion with him on using a dev/stable release model?
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Yes, and if you like you can also join in. It is a complex matter though. Today we did shine some light deep into all corners and some solutions appear to make sense in the beginning but then turn out to be an illusion.
Vedder doesn’t want to create an illusion where people think “this is safer or better or more trustable, stable etc.” while in reality it is not.
We came to the conclusion that the most important thing is building up the best test bed that we can envision today and intensify testing.
There will probably be a daily build branch for those who want to test the bleeding edge code, while the regular branch will focus on best possible reliability.
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Would love to. @Deodand and I are already chatting on a few items so perhaps all of us should get on the same page. I believe you have my contact info, thanks for the offer!
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It’s weird but my bootloader works but not for downgrading.
Right now I’ve updated from FW4.0 to FW4.2 without problems.
Forward ever, backward never…
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For only @Trampa hardware? Or for a variety of different platforms folks are using this on?
This may be why a community effort makes more sense than a vendor-led effort.
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Did you try to load 3.62 via SWD after you got the 4.2 installed successfully?
I did load FW 4.2 to get the latest wand FW and than went back to 3.62 without problems.
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Visibility into this test process to determine reliability would be nice
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I didn’t try to downgrade because the FW4.2 (test version) runs better than 4.0.
But maybe it’s a problem with usb of the master vesc because I had some disconnections (maybe time out) and couldn’t connect several times to Vesc-Tool.