P-2812HNU-Fx: NAND not detected by any U-Boot RAM image

Installing and Using OpenWrt
1

What I'm trying to do:

Install OpenWrt on what I thought was a P-2812HNU-F1, following the tutorials at https://blog.yucellmustafa.com.tr/2023/05/23/zyxel-p2812-openwrt and https://openwrt.org/toh/zyxel/p-2812hnu-f1.

What I did:

  1. I tested whether the router "just booted" before starting. It was booting correctly - and it was pre-configured for a FI provider (Elisa), based on the SSID (but I don't remember e.g. vendored UI changes - they look "like it looks online")
  2. Opened the case, connected a CH340E USB-to-TTL adapter to the serial header
  3. Shorted R17 while powering on to enter UART boot mode
  4. Uploaded u-boot.asc (F1 RAM image) via Tera Term serial
  5. U-Boot loaded successfully but nand erase.chip returned "no devices available" -- NAND showed as 0 MiB
  6. Discovered the PCB is actually an F3 board (part number 45-402-000351) in an F1 case
  7. Tried the F3 U-Boot RAM image -- crashes right after DRAM detection
  8. Tried four different U-Boot RAM images total -- none detect the NAND
  9. Never wrote anything to any flash

Where I am now:

Stuck. The router only boots into UART mode (CFG 02). The stock ZyXEL firmware should be untouched since no U-Boot image ever got far enough to write to flash. I tried cleaning R17 with isopropyl alcohol - but still the booting goes to UART mode.

And I still need a U-Boot build that actually supports my device.

Hardware deviations from documented P-2812HNU-F1 and F3 specs:

  1. Case label says F1, PCB is F3. Plastic housing sticker says P-2812HNU-F1. PCB part number is 45-402-000351, which matches the F3 (https://deviwiki.com/wiki/ZyXEL_P-2812HNU-F3).

  2. NAND chip matches neither F1 nor F3. Chip is Samsung K9F1G08U0C (PCB0). Documented chips are K9F1G08U0D (F1) and K9F1G08U0B (F3). The U0C is a different silicon revision.

  3. DRAM detected as 256 MiB. All U-Boot RAM images report DRAM: 256 MiB. Fx boards are listed as 128 MiB.

  4. No OpenWrt U-Boot RAM image detects the NAND. Tested four images total:

I have also read threads like in this forum (Zyxel p-2812 current state and updating wiki) and in the archived forum - but I don't see them any seeing the problem I hit

Boot Logs:

$ cat releases+24.10.1+targets+lantiq+xrx200+u-boot-p2812hnufx_ram+u-boot.md
.
ROM VER: 1.0.5
CFG 02
UART
************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************

U-Boot 2013.10-openwrt4 (Apr 14 2025 - 05:22:41) P-2812HNU-Fx

Board: Zyxel P-2812HNU-Fx
SoC:   Lantiq VRX288 v1.1
CPU:   125 MHz
IO:    125 MHz
BUS:   125 MHz
BOOT:  UART w/o EEPROM
DRAM:  256 MiB
NAND:  0 MiB
Using default environment

In:    serial
Out:   serial
Err:   serial
Net:   ltq-eth
P-2812HNU-Fx # nand info

P-2812HNU-Fx # 
P-2812HNU-Fx # 

$ cat openwrt-lantiq-p2812hnufx_ram-u-boot+r45578+r47026+F3.md
.
ROM VER: 1.0.5
CFG 02
UART
**************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************

U-Boot 2014.01-openwrt2 (Nov 15 2014 - 14:06:52) P-2812HNU-Fx

Board: ZyXEL P-2812HNU-Fx
SoC:   Lantiq VRX288 v1.1
CPU:   125 MHz
IO:    125 MHz
BUS:   125 MHz
BOOT:  UART w/o EEPROM
DRAM:  256 MiB

ROM VER: 1.0.5
CFG 02
UART
2

Since the device you have isn't the one supported, this isn't really surprising.

3

Could you explain more to me what does that mean? :sweat_smile:

From https://openwrt.org/toh/zyxel/p-2812hnu-f1, I see:
Supported Current Rel: 24.10.4

And all of the uboots I posted seem to be ... earlier than this version.

I don't mind if 24.10 (2024-Oct? https://openwrt.org/start#current_stable_seriesopenwrt_2512 says 2025-12) is the last supporting version. It is super hard to find an DSL modem/router supported by OpenWRT, that's easily + cheaply accessible on the second-hand market.
https://toh.openwrt.org/?columns=VIRT_edit,brand,model,version,cpu,cpucores,cpumhz,flashmb,rammb,modem,ethernet1gports,wlan24ghz,wlan50ghz,wlan60ghz,wlan600ghz,detachableantennas,VIRT_firm,firmwareopenwrtinstallurl,firmwareopenwrtupgradeurl,devicepage,VIRT_hwdata,oemdevicehomepageurl,wikideviurl,owrt_forum_topic_url,picture shows only 50 results out of a total 3K devices :confused:

HW tinkering is not my cup of tea - I don't want to risk buying something new and bricking it :confused:

I would also be curious why it is not supported anymore, if you'd offer that :folded_hands:
However ... https://firmware-selector.openwrt.org/?target=lantiq/xrx200&id=zyxel_p-2812hnu-f1 page seems to give Version 25.12.0 (r32713-f919e7899d) as a suitable version :confused:

4

Indeed, but as you've noticed F1 <> F3.

5

You see nand type down in OEM boot log, something attached to spiX.Y

6

The bootlog in the wiki, under Replacement of factory U-Boot, also shows 256MB ram. So I suppose that's an error in u-boot.
For the F3 you have to short at 2 places to get serial boot, not R17, but R15 and R24. I think this is because the F3 boots from NOR.

As your box boots unconditionally from serial, and u-boot detects no NAND, I think something is wrong with your NAND, and the serial boot is a fallback.
So thoroughly inspect the NAND pins. Maybe when shorting R17 something was damaged, or shorted?