In order to flash the Bigtreetech Octopus V1 using my STLinkv2 debug adapter, I needed. First we need to note that the first 32k of flash memory are occupied by the bootloader (0x08000000 to 0x08008000). So we need to flash the firmware at address 0x08008000. By default, this is not configured correctly in Marlin.
Open ini/stm32f4.ini and edit the [env:BIGTREE_OCTOPUS_V1]:
[env:BIGTREE_OCTOPUS_V1]
platform = ${common_stm32.platform}
extends = stm32_variant
board = marlin_BigTree_Octopus_v1
board_build.offset = 0x8000
board_upload.offset_address = 0x08008000
build_flags = ${stm32_variant.build_flags}
-DSTM32F446_5VX -DUSE_USB_HS_IN_FS
upload_protocol = stlink
Note that you absolutely need to re-flash the bootloader in case you accidentally flashed with the old configuration. Follow the official documentation in order to flash the bootloader. I flash usin STM32CubeProgrammer 2.7.0 (2.8.0 does not work) on both Linux and Windows.
The [env:BIGTREE_OCTOPUS_V1_USB] will be updated automatically as it includes [env:BIGTREE_OCTOPUS_V1]