Lakritz Computer

Lakritz is an FPGA computer designed by Lone Dynamics Corporation.

This repo contains schematics, PCB layouts, pinouts, a 3D-printable case, example gateware and documentation.

Find more information on the Lakritz product page.

Programming Lakritz

Lakritz has a JTAG interface and ships with a DFU bootloader that allows the included flash MMOD to be programmed over the USB-C port.

DFU

The DFU bootloader is available for 5 seconds after power-on, issuing a DFU command during this period will stop the boot process until the DFU device is detached. If no command is received the boot process will continue and the user gateware will be loaded.

Install dfu-util (Debian/Ubuntu):

$ sudo apt install dfu-util

Update the user gateware on the flash MMOD:

$ sudo dfu-util -a 0 -D image.bit

Detach the DFU device and continue the boot process:

$ sudo dfu-util -a 0 -e

It is possible to update the bootloader itself using DFU but you shouldn't attempt this unless you have a JTAG programmer (or another method to program the MMOD) available, in case you need to restore the bootloader.

JTAG

These examples assume you're using a "USB Blaster" JTAG cable, see the header pinout below. You will need to have openFPGALoader installed.

Program the configuration SRAM:

openFPGALoader -c usb-blaster image.bit

Program the flash MMOD:

openFPGALoader -f -c usb-blaster images/bootloader/tinydfu_lakritz.bit

Blinky

Building the blinky example requires Yosys, nextpnr-ecp5 and Project Trellis.

Assuming they are installed, you can simply type make to build the gateware, which will be written to output/lakritz.bit. You can then use openFPGALoader or dfu-util to write the gateware to the device.

Linux

See the Kakao Linux repo for the latest instructions.

Prebuilt Images

Copy the files from the images/linux and images/v0/25f directory to the root directory of a FAT-formatted MicroSD card along with the files from the images directory in the Kakao Linux repo.

Lakritz ships with LiteX gateware on the user gateware section of the MMOD that is compatible with these images. After several seconds the Linux penguin should appear on the screen (HDMI) followed by a login prompt.

Building Linux

Please follow the setup instructions in the linux-on-litex-vexriscv repo and then:

1. Build the Linux-capable gateware:

$ cd linux-on-litex-vexriscv
$ ./make.py --board lakritz --uart-baudrate 115200 --dcache-size 64 --icache-size 64 --dcache-ways=1 --icache-ways=1 --dtlb-size 2 --itlb-size 2 --build

NOTE: This may fail, if so:

$ cd build/lakritz/gateware

Edit lakritz.ys and add the -abc2 option as shown below:

synth_ecp5  -top lakritz -abc2

Now run:

$ bash build_lakritz.sh

2. Write the gateware to the MMOD using USB DFU:

$ sudo dfu-util -a 0 -D build/lakritz/gateware/lakritz.bit

3. Copy the device tree binary build/lakritz/lakritz.dtb to a FAT-formatted MicroSD card.

4. Build the Linux kernel and root filesystem:

$ cd ..
$ git clone http://github.com/buildroot/buildroot
$ cd buildroot
$ make BR2_EXTERNAL=../linux-on-litex-vexriscv/buildroot/ litex_vexriscv_usbhost_defconfig

Optionally customize the kernel and buildroot packages:

$ make menuconfig

Build the kernel and rootfs:

$ make
$ ls output/images

5. Copy the Image and rootfs.cpio files from output/images to the MicroSD card.

6. Copy the OpenSBI binary (included in this repo as lakritz/images/linux/opensbi.bin) to the MicroSD card. Alternatively, you can build this binary by following these instructions.

7. Copy lakritz/images/linux/boot.json to the MicroSD card.

8. Power-cycle Lakritz. After Linux has finished booting you should see a login prompt on the HDMI display.

JTAG Header

The 3.3V JTAG header can be used to program the FPGA SRAM as well as the MMOD flash memory. It can also be used to provide power (5V) to the board.

2 4 6
1 3 5

Pin	Signal
1	TCK
2	TDI
3	TDO
4	TMS
5	5V0
6	GND

Resources

• fpga-dac audio player

Board Revisions

Revision	Notes
V0	Initial version

License

The contents of this repo are released under the Lone Dynamics Open License with the following exceptions:

• The KiCad design files contain parts of the kicad-pmod library which is released under the Apache License, Version 2.0.

• The KiCad design files may contain symbols and footprints released under other licenses; please contact us if we've failed to give proper attribution.

Note: You can use these designs for commercial purposes but we ask that instead of producing exact clones, that you either replace our trademarks and logos with your own or add your own next to ours.