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could anybody explain what is this download mode?

As described in here How to root Innos A35 as I hold vol up +vol down 5 seconds and at the same time connecting the USB cable to my computer it shows up a removable disk and unknown drivers in windows 7.

My phone is also Innos A35 device locally sold as i35 from dialog telecom.

What are those? And what is this download mode?

But unlike the recovery mode, I didn't get a screen up. Is these two modes all coming from ROM. what kind of code is there on ROM. [Well in x86 computer I could review a opensource bios implementation, any idea on Android ARM ?].Where that consoles come from?

Where is uboot located? Is this download mode is a mode that programmed into a ROM, where I could not change it?

I have read the boot procedure of a typical android phone. But can't organize the info with this.

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    Download mode is for flashing radio firmware/rom upgrade through official means..its an open-ended question as there's no reference of your device that spurred the question on... can you include your device please? – t0mm13b May 22 '13 at 0:32
  • my device is innos A35 as well. – sandun dhammika May 22 '13 at 0:36
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    Some devices uses U-Boot over the generic boot, its a bootloader code found in the /boot partition, for details of boot - see this As for Download mode, for example ODIN is commonly used on Samsung devices to flash ROMs, those devices needs to be in download mode prior to flashing. – t0mm13b May 22 '13 at 0:46
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    @t0mm13b I'd say you should merge your two comments into an answer :) – Izzy May 22 '13 at 7:15
  • if that is a partition under linux/android. you tell me how this happen? In wikipedia page it said that bootcode is completely isolated from the android/linux itself. Could you please explain that also to me in your answer. – sandun dhammika May 22 '13 at 12:41
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Download mode is for flashing radio firmware/ROM upgrade through official means.

Some devices uses U-Boot over the generic boot, it is a boot-loader code found in read-only ROM chip on the board, which uses a certain memory address offset, in which the kernel from the /boot partition gets loaded into that specific certain memory address offset and jumps into that address and the kernel starts running.

For details of the generic LK boot which is employed by most, if not all, Qualcomm based devices, see this

As for Download mode, for example ODIN is commonly used on Samsung devices to flash ROMs, those devices needs to be in download mode prior to flashing. However, ODIN is not the official way to do it, rather Kies, is the official route in upgrading the firmware, this is for Samsung devices for example.

  • I've reviewed your answer that you referenced 'this' . It seems like you are a great kernel hacker. – sandun dhammika Jun 22 '13 at 17:17
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The device has both "download mode" and "bulk mode" as part of the SOC. When it is turned on, it decides if it should jump to any of those modes, or actually boot the "main processor". If it does, then the preloader/secondary bootloader (two different names for the same thing) kicks in. If you turn the device on, the preloader will run the bootloader (on QC devices usually the lk that was referred on another answer).

The bulk mode is meant to expose, in bulk, the device's partitions. The download mode is meant to be used to push a programmer into the device and run it.

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