Recovering bricked Ambarella DVR

xmichael

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Hello. Just bricked my DVR by flashing .bin firmware from different vendor (from similar device)... The device is on A7LA70 SoC. There is "ESR818" written on PCB.
The problem is that I can not connect it to PC in recovery mode. I figured out that connecting cable while pressing "Menu" button brings device in different state that simply powering it on or plugging cable in (though also tried other buttons). Then OS tries to detect USB device but it fails. On Windows it fails with "Unknown device", and says that device reported failure and cannot be connected (so I can not even try to install driver manually). On Linux it fails with "unable to enumerate USB device" and different error codes (-110, -73...).
I tried 3 different miniUSB cables, connecting to different ports on PC, but no luck. I know that I should try connecting with OTG cable, and I will try today... So here is my questions:
  1. Is there any lower level possibilities to load firmware to device (JTAG etc)?
  2. Is there a way that wrong firmware may damage some code responsible to recovery mode?
  3. At this moment I only have few .elf's from the vendor of my DVR, but for different models (A7L50D and different sensor). Can it be used to recover my DVR and then flash stock .bin firmware at all?
 
It is "RoverEye Tesla A7 Dual". By googling label from PCB I've found (probably) original device "E-SONG ESR818". Not sure if I can safely place URL there (though there is an URL in start post). I made a photo of PCB, and may attach it some later, if it helps...

ADD: I've bricked my DVR with a .bin firmware of "Inspector FHD-A770"
 
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I've made another miniUSB OTG cable, and it worked. While my DVR is recovered, the question #2 remains opened:
Is there a way that wrong firmware may damage some code responsible to recovery mode?
For example if I flash random .bin from sd card or .elf from DirectUSB? Is there a possibility that I wouldn't be able to recover device using DirectUSB?
 
if you load an incorrect firmware it is possible to brick it completely, if you have the correct elf file and have USB access though they're very hard to get to a state where you can't recover them
 
So the keyword is "correct elf file and USB access" I would like to add one more is "correct button to press for Ambarella Evaluation Board 1.2.3.0 to be found by PC"
 
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