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How the mobile phone (that is off) informs the Windows PC (with installed drivers "MediaTek PreLoader USB VCOM port" and "MediaTek USB Port") how to identify itself: as device - "MediaTek PreLoader USB VCOM port" or as - "MediaTek USB Port"?

When I plug the phone to USB, Windows PC connect it sometime through "preloader USB", sometimes through "just USB" ports, sometimes both in sequence (I see it from WMI events). I don’t see any pattern related to "time after next attempt" or "volume buttons pressed".

P.S This is "the phone off" state when battery is inside. What are correct names for those states (battery "in" and "outside")? When battery is extracted - device is not recognized as USB device by PC.

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I can't see the question here ?

Are you asking what the driver is for ?

Please have a look at this video to understand what the preloader is, MTK Backup & Restore

The Mediatek Preloader is used for flashing new image's to your device.

Their is two different boot loaders on Mediatek device's..

  1. MTK DA USB - For flashing the Preloader
  2. MTK Preloader - For flashing all other image's

How does it register as a device while it's off ?
This is so you can fix your device when it won't even turn on, it need's to be before the boot of your system.

I hope i somehow answered the question here.

  • Thank you. It is become more clear. But I still do not understand how the device decide that "at this moment I should be handled by MediaTek PreLoader USB VCOM port but next time as MediaTek USB Port" ? This is what I observe when plug the phone (that is off) to the USB. Sometimes it is connected through “MediaTek USB Port” driver sometimes as for "MediaTek PreLoader USB VCOM port" driver... Answer could be "when you press the volume button it will be handled with PC preloader port driver" (but the problem is that I do not press any buttons and it is still get variety of results) – Roman Pokrovskij Dec 10 '18 at 10:08
  • I have always had my MTK device's do this... It is because the Preloader only connects very shortly, it requires the PC to make a Handshake to hold the connection... If the PC doesn't make a Preloader Handshake, it'll drop the preloader and connect via Meditek USB Port ( CDC ) instead of Preloader... As fas as i can tell, it's just a fail safe – Gadget Guru Dec 10 '18 at 21:15
  • Also, i believe on some older models, you could hold volume down or up. and it'd hold the preloader connection open, for easier driver installation... It gets annoying using device manager because as your about to click on the port and install the driver, it disappears or change's, making driver installation really annoying. I've always found it easier to manually install the drivers prior to connecting the device. – Gadget Guru Dec 10 '18 at 21:22
  • But that is not what I observe with my Alcatel Pixi 3. As I said - I observe totally random behavior: sometimes handshake for "just USB" sometimes for "preloader USB", sometimes (very rare) two in sequence as you said (but with different order: "just USB" first "preloader USB" second). I have tried buttons but they do not change anything. Lets decide this is a kind of bug. What kind of program (how you call it) propose handshakes? – Roman Pokrovskij Dec 10 '18 at 21:26
  • I mean "What kind of program run on the phone when it is off (but battery is inside)?" Is it a "BootRom" - I have met this term several times.. – Roman Pokrovskij Dec 10 '18 at 21:40

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