RISC-V on the ULX3S with LiteX - Part 2

First .. the exciting news: With 24 days still left in the Crowd Funding Campaign, the ULX3S is within a few dollars of reaching their $40K stretch goal!! I'm so happy to see their success. I've been super happy with mine. (Edit: now nearly 300% funded by the time I publish this!)

TL;DR: Check out this soft_cpu.sh script used to create a soft RISC-V CPU on the ULX3S.

Back to my fomu! I revisited the Adafruit Feather M0 Express - A request for the USB device descriptor failed: Issue #293 on GitHub in the hathach/tinyusb repo. The suggestion was to simply update my fomu to see if the Feather M0 problems would go away:

The last few lines of the release.sh

dfu-suffix -v 1209 -p 70b1 -a $output/${platform}-updater-${release}.dfu
dfu-suffix -v 1209 -p 70b1 -a $output/${platform}-foboot-${release}.dfu

but I saw an error when trying to do that:

C:\Download\dfu-util>dfu-suffix -v 1209 -p 70b1 -a fomu\hacker-updater-v2.0.3.dfu
dfu-suffix (dfu-util) 0.9

Copyright 2011-2012 Stefan Schmidt, 2013-2014 Tormod Volden
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/

Please remove existing DFU suffix before adding a new one.

so I next tried using dfu-util, as noted here:

C:\Download\dfu-util>dfu-util -D fomu\hacker-updater-v2.0.3.dfu
dfu-util 0.9

Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2016 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/

Match vendor ID from file: 1209
Match product ID from file: 70b1
Opening DFU capable USB device...
ID 1209:5bf0
Run-time device DFU version 0101
Claiming USB DFU Interface...
Setting Alternate Setting #0 ...
Determining device status: state = dfuIDLE, status = 0
dfuIDLE, continuing
DFU mode device DFU version 0101
Device returned transfer size 1024
Copying data from PC to DFU device
Download        [=========================] 100%       112828 bytes
Download done.
state(7) = dfuMANIFEST, status(0) = No error condition is present
state(8) = dfuMANIFEST-WAIT-RESET, status(0) = No error condition is present
Done!

Since that seems to have been successful, I will return to the ULX3S for now.

A quick check of the rxrbln/picorv32 ULX3S fork that is is included in my full toolchain install and I'm still not yet able to build:

gojimmypi@ubuntu:~/workspace/rxrbln-picorv32/picosoc$ git fetch
gojimmypi@ubuntu:~/workspace/rxrbln-picorv32/picosoc$ git pull
Already up to date.
gojimmypi@ubuntu:~/workspace/rxrbln-picorv32/picosoc$ make
iverilog -s testbench -o hx8kdemo_tb.vvp hx8kdemo_tb.v hx8kdemo.v spimemio.v simpleuart.v picosoc.v ../picorv32.v spiflash.v `yosys-config --datdir/ice40/cells_sim.v`
picosoc.v:70: error: NULL port declarations are not allowed.
Makefile:20: recipe for target 'hx8kdemo_tb.vvp' failed
make: *** [hx8kdemo_tb.vvp] Error 1
gojimmypi@ubuntu:~/workspace/rxrbln-picorv32/picosoc$ 

So ok, I'll give that one some more time.

Refresher on getting Micropython onto the fomu:

cd /mnt/c/workspace
mkdir -p fomu
cd fomu
wget https://github.com/im-tomu/fomu-workshop/raw/master/micropython-fomu.dfu
dfu-util -D micropython-fomu.dfu

Should give an output like this:

dfu-util 0.9

Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2016 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/

Match vendor ID from file: 1209
Match product ID from file: 5bf0
Opening DFU capable USB device...
ID 1209:5bf0
Run-time device DFU version 0101
Claiming USB DFU Interface...
Setting Alternate Setting #0 ...
Determining device status: state = dfuIDLE, status = 0
dfuIDLE, continuing
DFU mode device DFU version 0101
Device returned transfer size 4096
Copying data from PC to DFU device
Download        [=========================] 100%       136164 bytes
Download done.
state(7) = dfuMANIFEST, status(0) = No error condition is present
state(8) = dfuMANIFEST-WAIT-RESET, status(0) = No error condition is present
Done!

Mine showed up as COM8 and For more details on how a RISC-V soft CPU runs MicroPython, see the Fomu as a CPU section of the fomu workshop.

I've been following along with the development of picosoc for the ULX3S. This is included in the full toolchain build, or can be fetched from here:

cd $WORKSPACE
git clone https://github.com/rxrbln/picorv32.git

To build:

# use the rxrbln firmwware
cd $WORKSPACE/rxrbln-picorv32/picosoc

# there have been some recent additions to the source code; some files not included in the repo
# so get an older, know-to-compile version:
git checkout b1cd395b

make ulx3s_fw.img
$WORKSPACE/ulx3s-examples/bin/ujprog.exe -j FLASH -f 0x200000 ulx3s_fw.img

Use the LiteX CPU

# make the soft CPU
cd $WORKSPACE/litex-boards/litex_boards/targets
./ulx3s.py --device LFE5U-85F --cpu-type picorv32

# show the files built
echo "ULX3S Gateware:"
ls $WORKSPACE/litex-boards/litex_boards/targets/soc_basesoc_ulx3s/gateware -al

echo "ULX3S BIOSL"
ls $WORKSPACE/litex-boards/litex_boards/targets/soc_basesoc_ulx3s/software/bios -al

# put the soft CPU on the ULX3S
cd $WORKSPACE/litex-boards/litex_boards/targets/soc_basesoc_ulx3s/gateware
$WORKSPACE/ulx3s-examples/bin/ujprog.exe top.bit

cd $WORKSPACE/litex-boards/litex_boards/targets/soc_basesoc_ulx3s/software/bios
litex_term --serial-boot --kernel bios.bin /dev/ttyS15

Press enter, and you should see a litex> prompt. Type reboot As a reminder, if you keep getting an error like this:

ULX2S / ULX3S JTAG programmer v 3.0.92 (built Feb 18 2019 10:55:47)
FT_Open() failed
Cannot find JTAG cable.

Check to make sure NOTHING is using the ULX3S, including perhaps a litex_term or putty session. (yes, I've bumped into that more than once).

A big Thank You to @GregDavill  for these tips on the twitter thread:

The LiteX bios is what you're seeing running.  

By default, LiteX builds this to execute from address 0x00000000. This is an address space inside the FPGA, using blockram. Litex embeds the code inside so it's baked into the bit-stream. 

uart_sync() just waits until internal uart FIFOs are cleared. (Which ensures that printf data  has been sent to the PC...) printf also relies on interrupts, so once you've disable interrupts printf no longer works.

The bios exists to initialise things like SDRAM, which you can see it doing here. It then tries to load a USER program from SD/FLASH/Serial/Ethernet.

According to the timvideos "what is litex" the flterm program is what is needed to interact with the bios. As of the date of this blog, I've included that in the full ULX3S toolchain install.

Beware there's an old implementation of traps on riscv32 that may cause code crashes. (e.g. soft debugging)

I found an example using flterm: This next section is an unsuccessful attempt to upload firmware with flterm. (it just sits there waiting for something)

cd $WORKSPACE/flterm
./flterm --port /dev/ttyS15 --kernel $WORKSPACE/rxrbln-picorv32/firmware/firmware.bin --kernel-adr 0x40000000

Searching for the term "liftoff" and I found two occurrences here and here:

# remote.origin.url=https://github.com/enjoy-digital/litex

# this is the one that gets compiled:
C:\workspace\litex\litex\soc\software\bios\boot.c

# plus this older file:
C:\workspace\litex-buildenv\third_party\litex\litex\soc\software\bios\boot.c

I created a soft_cpu.sh script soon to be pushed to the ulx3s-toolchain setup to illustrate how I created a picorv32 soft CPU on the ULX3S using LiteX. See my next blog on updating the firmware.