Running an initramfs-image from RAM should be a safe option.
I tried to access the bootloader to start an OpenWrt-image, or at least to be able to recover if something went wrong.
I connected ground of my serial interface to TP5.
TP4 seems to be 3.3V
TP2 is TX (connect to RX of the serial interface)
I thought TP1 might be RX, but TP1 seems to be pulled to ground.
I can see output from the bootloader (u-boot 1.1.3). But I cannot interrupt it, I cannot send commands to the bootloader.
Did anybody had more luck than I?
Did anybody found TP3?
This is the output from the bootloader:
cid reg:00010102, cid:1[04010D07][04010D0A]
DDR Calibration DQS reg = 00008988
DDR Calibration MEMCTRL reg = 0E120003
U-Boot 1.1.3 (Nov 28 2020 - 10:44:01)
Board: Ralink APSoC DRAM: 64 MB
relocate_code Pointer at: 83fb8000
flash manufacture id: 20, device id 70 17
Warning: un-recognized chip ID, please update bootloader!
*** Warning - bad CRC, using default environment
============================================
Ralink UBoot Version: 5.0.0.0
--------------------------------------------
ASIC 7628_MP (Port5<->None)
DRAM component: 512 Mbits DDR, width 16
DRAM bus: 16 bit
Total memory: 64 MBytes
Flash component: SPI Flash
Date:Nov 28 2020 Time:10:44:01
============================================
icache: sets:512, ways:4, linesz:32 ,total:65536
dcache: sets:256, ways:4, linesz:32 ,total:32768
##### The CPU freq = 580 MHZ ####
estimate memory size =64 Mbytes
RESET MT7628 PHY!!!!!!
Please choose the operation:
1: Load system code to SDRAM via TFTP.
2: Load system code then write to Flash via TFTP.
3: Boot system code via Flash (default).
4: Entr boot command line interface.
7: Load Boot Loader code then write to Flash via Serial.
9: Load Boot Loader code then write to Flash via TFTP.
default: 3
You choosed 3
0
3: System Boot system code via Flash.
tplink_turn_off_led
## Booting image at bc020000 ...
text base: 80000000
entry point: 8000c150
Uncompressing Kernel Image ... OK
No initrd
## Transferring control to Linux (at address 8000c150) ...
## Giving linux memsize in MB, 64
Starting kernel ...