Kaltstahl is a higher capacity version of Blaustahl.
Kaltstahl can use either the Blaustahl (USB-CDC) or Ebenstahl (USB-MSC) firmware.
The default firmware images are available here.
Please see the Blaustahl repo for instructions and firmware source code for the USB-CDC firmware.
To build the firmware from the source code, you will need to modify blaustahl.h and change the FRAM_SIZE value to 262144 and then use the following commands:
$ mkdir build
$ cd build
$ cmake -DPICO_DEFAULT_BOOT_STAGE2_FILE=/your-pico-sdk-directory/pico-sdk/src/rp2040/boot_stage2/boot2_generic_03h.S ..
$ make
The contents of this repo are released under the Lone Dynamics Open License.