eventually I found from https://www.rigacci.org/wiki/doku.php/doc/appunti/android/sp_flash_tool that the flasher is available for linux (binary only). if it works with my glibc, this could make it much easier to work with.
I also took a usb log of the windows flasher using usbpcap. unfortunate since the flasher speaks in com ports.
the links from that website jump to various shady binaries, there's something called "miracle box" that can flash most devices, and is closed source.
my phone is no longer providing usable tethered internet (~5KB/s when lucky), but works fine nontethered. maybe some business agreement.
2022-05-03 0928 ET
so i'm downloading things to the phone and transferring them off adb, which for some reason does not always work, but has been recently.
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the linux flash tool launched fine on my ancient glibc, great. unfortunately it says my scatter file is invalid.
on the web links they talk about generating scatter files.
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the provided sp flasher has "custom" after it. could be related.
this flasher has more options, like readback and memory test.
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my vendor scatter file is name MT6771_Android_scatter.txt
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so it turns out the partition map ("scatter file") format is forward compatible for _minor_ version numbers. so my scatter file for v3.2128 does not work on v6.1520 but finally _does_ work on linux sp flash v5.2208 . v6 also has the issue of changing the format to xml.
I just downloaded all the partitions from linux for the first time!
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