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Pergola FPGA

The Pergola FPGA board is a low-cost, open-source FPGA development board featuring the Lattice ECP5 FPGA.

Pergola FPGA top view

Current status

RevA 0.1

A handful of units have been built for initial test and bringup populated with LFE5U-12F-8BG256C.

It has been tested and works if the fixes below are applied.

Errata:

  • iMX ROM bootloader freezes because the UART RX pin is pulled low by the FPGA during boot. (FPGA pin is PL35B_VREF_1_6) A 4K7 pull-up is probably not enough, the voltage drops to 2.9V. Workaround: Bodge a 1K pull-up between UART_RX and 3V3.
  • Wrong load caps for the xtal. Should be 20pF.
  • SWD IO and CLK are swapped on the silk.
  • IMX_BOOT_MODE_0 and IMX_BOOT_MODE_1 are swapped on the silk.
  • A 1K pull-down is on the ~FPGA_HOLD~ net to allow the iMX to use the flash exclusively during boot-up.

Firmware

TODO.

Currently I have a very ugly test project that can be loaded into the iMX's RAM using the ROM bootloader. This will open up a CDC interface that can be used to send a bitstream to the FPGA.

Currently working on porting the UF2 bootloader in order to update the firmware easily using USB and not having to use the SWD pins.

Current horrible hack is located over at git.xil.se and contains a prebuilt binary.

The firmware will expose a cdc_acm device over USB. To program a bitstream, you simply have to write the number of bytes it is, followed by a newline (\n), followed by the bitstream.

Getting started

  • Clone my fork of the imx usb loader project:
git clone https://github.com/kbeckmann/imx_usb_loader && cd imx_usb_loader
  • Checkout the imxrt1010 branch:
git checkout imxrt1010
  • Build it:
make
cd .. && git clone https://github.com/pergola-fpga/pergola && cd pergola/firmware
  • Run the loader:
../../imx_usb_loader/imx_usb

. You might have to run it with sudo.

  • Check dmesg to see if you got a cdc_acm device, e.g. ttyACM0
  • Now you'll be able to send a bitstream to the board:
export ACM_DEVICE=/dev/ttyACM0
export PROGRAM_BIN=path/to/your/top.bin

# If you don't have setup udev rules
sudo chown $UID:$GID $ACM_DEVICE

# Configure the ACM device to be raw, this prevents weird stuff from happening when we send raw binary data.
stty -F $ACM_DEVICE 300 raw -clocal -echo icrnl;
sleep 0.01;
cat $ACM_DEVICE &;
echo -n "$(stat -c%s $PROGRAM_BIN)\n" > $ACM_DEVICE;
cp $PROGRAM_BIN $ACM_DEVICE; sync
  • This should generate the following output more or less:
Reading 582369 bytes
READ_ID: ff ff ff ff 21 11 10 43

Done programming. FPGA_DONE=1
P E R G O L A

<bytes to load><\n>; Load bitstream to FPGA SRAM
  • There is also an nmigen board definition in gateware/nmigen_wip/pergola.py

How to contribute

Feel free to submit a PR, create an issue.

Discussion happens on Gitter for the time being. You can also ping @kbeckmann on Twitter.

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Low-cost ECP5 FPGA development board

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