IMPORTANT! If you want HELP in case of a bricked Garmin device, please follow this

**Neil** · 24th February 2025, 01:33 AM

Yes, Garmin's ARM processor is indeed customised. It's of course "ARM-like" however operates and boots the device in a "Garminized" kind of way. kunix supplied us with an insight as follows:

Spoiler: click for quote

Try reading the following [Only registered and activated users can see links. ], it's a typical boot sequence of an embedded ARM-based device, including Garmin devices.
So, I can tell the same story of the boot sequence the Garmin-ish way:

When you power on your device, the ARM processor starts executing it's ROM code.
The external RAM modules are not initialized yet, so ROM code would have to use the internal SRAM for stack and data.
ROM code searches for x-loader somewhere, the copies it to SRAM and executes it.
On debug motherboards ROM code can load x-loader from SD/MMC or over UART.
But on release Garmin motherboards ROM code loads x-loader only from starting blocks of the external flash chip. So if you erase those blocks, you will never boot your device again.
Also those blocks are known as region 43.
x-loader is made by Garmin, so it "knows" a lot about the hardware setup.
x-loader initializes the external RAM. Then, if the external flash chip is NAND, it loads bootloader from region 5 to RAM and executes it.
Alternatively, if the external flash chip is NOR, the bootloader's addresses are mapped to the address space of the CPU (I don't know, whether x-loader sets up the mapping or it's done by the hardware setup), and so in this case bootloader can be executed from flash directly.
Bootloader (the "u-boot") enters the pre-boot mode if a particular key combination is pressed, or if region 14 doesn't pass the "5A A5" test.

In the pre-boot mode the bootloader and the program on the PC (updater.exe, for example) communicate using the Garmin USB protocol.
If not entered the pre-boot mode, bootloader proceeds to execute fw_all.bin.
If the external flash chip is NAND, bootloader loads fw_all.bin from region 14 and executes it.
If the flash chip is NOR, bootoader executes fw_all.bin from flash directly.
If you erase bootloader in region 5, you will never boot your device again (most probably, because maybe x-loader can load bootloader from SD, but it's highly doubtful).
fw_all.bin (the "kernel") is responsible for
- drawing the usual GUI
- for providing the mass storage mode and the MTP mode.
- initiating the procedure of executing update.txt scipts.
- initiating the procedure of flashing GUPDATE.GCD files and verifying GUPDATE.GCD digital signature.
- also, if not in the mass storage/MTP mode, it can communicate with the PC using the Garmin USB protocol and it provides a very rich set of USB commands
boot.bin (the "ramloader") is responsible for:
- flashing regions over USB in pre-boot mode. It also communicates with with the PC using the Garmin USB protocol.
- very frequently boot.bin contains copies of bootloader and x-loader and flashes them, when executed.
- flashing regions from GUPDATE.GCD files.
- executing update.txt scripts.

Every piece of Garmin firmware (i.e., x-loader, bootloader, fw_all.bin, boot.bin) contains a table of regions, which specifies which regions are contained on which flash chip and where exactly.
Also people frequently confuse bootloader and boot.bin. They are different.
Also region 41 (NV) is parsed only by fw_all.bin, other pieces of firmware (x-loader, bootloader, boot.bin) treat it as an opaque massive of bytes.
So if NV is corrupt, fw_all.bin may crash even when entering the mass storage/MTP mode.
But other pieces of firmware (x-loader, bootloader, boot.bin) continue working correctly.

I can add that the Garmin OS of your 1390, although Linux-based, is very far from basic Linux and is a proprietary "closed-shop". We can garden around the edges by modifying firmware but AFAIK nobody has actually been able to get into the OS proper or if they have done, they haven't made it pubic.

**nsPerFoot** · 25th February 2025, 10:29 PM

Interesting! It implies that simply replacing a bad flash IC and/or the controller will go nowhere without reprogramming at least some of the firmware into the new flash. Without a JTAG programmer, fixturing, and other resources - oh well! Thanks for the info; it says Garmin keeps everything completely programmable on their side, which isn't a bad strategy for a consumer device that will likely get updates, etc. as well as optional paid features like maps.

**Neil** · 26th February 2025, 01:01 AM

Originally Posted by nsPerFoot

... It implies that simply replacing a bad flash IC and/or the controller will go nowhere without reprogramming at least some of the firmware into the new flash. Without a JTAG programmer, fixturing, and other resources ......

Yes that's it precisely, and it's what i was saying in Post #398 in fact. There are JTAG contacts on release boards i believe. But i don't know where exactly and of course they are hard to program even when JTAGs are known. Like i said, Garmin is a closed shop - at least to us mere mortals.

**Zakk** · 3rd March 2025, 12:13 AM

@Neil
Thanks, don't think it is worth it to spend much time trying to fix it as these are cheap and aplenty on the used market. New update didn't even have much important that bothered me but the settings not saving will probably be a bit tough to deal with.

**Neil** · 3rd March 2025, 01:26 AM

@Zakk
Absolutely agree.

**Zakk** · 15th May 2025, 05:08 AM

1) Bricked device MODEL, Firmware version, HWID.
Nuvi 255W, V7.80 but also 4.20, 827
2) Why and how the device got bricked.
I was following Butters' tutorial on converting the 2x5w series to 465 to get Lane assist, and flashed the hybrid firmware with no issues. I flashed the full 0943 firmware, and the device updated with updater.exe, I saw the pc connection screen on the Nuvi's display and then disconnected it, but as I disconnected it I saw a glimpse of the "software loading" screen or something of the sorts (I forgot the exact text but it was the loader text)
3) Symptoms: what's wrong in your device?
It's just on a black screen now, it might be important to mention that the battery on this nuvi has been kaput for a while.
4) Does your pc sees your device ?
Not as far as I know
5) List all the procedures you already tried to unbrick it and their results and errors messages obtained.
Trying to turn it on lol, no result
6) Do you have Garmin USB Drivers installed ? Garmin: USB Drivers Updates & Downloads
Yes
7) If you don't know HWID get it by Use program G7ToWin to retrieve your HWID
827
8) Write down if you already read and tried everything in these two threads: GarminCure3 tool - the new way to create cure firmwares for Garmin devices and How to unbrick a nüvi - step by step guide
N/A as the device can't reach preboot
9) Can you reach preboot mode? If no ,have you followed this? Garmin devices preboot mode
No
10) Probably no , but do you have NV backup?
I believe so, it's a file called "41.bin" and I was told to make a backup at the start of the tutorial

**Neil** · 15th May 2025, 12:39 PM

Likely you've disconnected it from the PC (which was the power source) while it was still updating. So, if the battery was flat the flash was aborted which can have nasty results when essential regions maybe have been corrupted or erased. If the screen has now become unresponsive that in turn means it's not able to attain preboot mode by holding the screen of course. The only other way to possibly revive it is by directly flashing regions from SD card ..... however if preboot is not available due to any other reason than a non-functioning screen you're royally screwed because the card isn't even looked for until the device partially boots.

It may still have HWID of 0827 or it might now be 0943 so you could try the SD function by attempting to flash back the original 2x5W firmware. You'll need to use TWO folders in the Garmin/Updater folders named 0827 and 0943 both with the 0827 Ldr.bin, and of course the 0827 firmware. If you don't know how to do that then post again and i'll make a kit for you when i have time if no one else does it meanwhile.

**Zakk** · 15th May 2025, 03:44 PM

Im pretty sure that I'm in the royally screwed category, Not sure if you'd think it would be worth trying to revive it with an SD card with the firmware kit on it, but if so then I'd appreciate a little guide on what steps to take next

**Neil** · 16th May 2025, 12:11 AM

Well it's purely a shot in the dark that i suggested you try an SD card cure. That's based on the chance of the lack of preboot access being because of a non-responsive screen rather than a bricking due to a bad flash.

I note now however that you said it has HWID "827" in response to Point 7 ("If you don't know HWID get it by Use program G7ToWin to retrieve your HWID"). So, if indeed you got that from G7ToWin AFTER the failed flashing ('cos it relies on preboot connection), it may even have corrupt or missing data in region 14 where the main system software (fw_all.bin's data) is stored. If that's the case the device will have defaulted to preboot mode spontaneously without user input. Therefore, if you haven't already checked please do so now to determine if it's seen under Windows Device Manager (not Disk Management or File Explorer)). Try while holding the screen anyway, connect it to your PC with the GUI of Device Manager open to see if it appears in the list as "GARMIN Device" and/or if there is any Windows device connection "du-dut" sound played.

Spoiler: Image