meowzor post draft
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Jade Lovelace
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|
|||
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|
||||
date = "2023-04-20"
|
||||
draft = true
|
||||
path = "/blog/i-built-a-meowzor"
|
||||
tags = []
|
||||
title = "I built a Meowzor robot for class"
|
||||
+++
|
||||
|
||||
As part of the requirements for the third year design studio class for Computer
|
||||
Engineering at UBC, I worked on a group project using a FPGA, electronics, and
|
||||
other pieces. We had to pick a project idea and then build it in a 4 month term
|
||||
as a group of 3 or 4 (we were 3). The group I was in built a robot called
|
||||
Meowzor that points a laser in front of a cat, using an object detection model
|
||||
to find where the cat is and commanding the laser robot accordingly.
|
||||
|
||||
You can see our presentation video here:
|
||||
|
||||
<iframe width="560" height="315" src="https://www.youtube-nocookie.com/embed/JyZmC07ff0Q" title="YouTube video player" frameborder="0" allow="clipboard-write; picture-in-picture; web-share" allowfullscreen></iframe>
|
||||
|
||||
This is the robot itself:
|
||||
|
||||
{% image(name="meowzor-board.jpg", colocated=true) %}
|
||||
Piece of plywood with a DE1-SoC development board on it next to a breadboard
|
||||
with stepper drivers and a 3d printed assembly with a rotation/pitch stage.
|
||||
{% end %}
|
||||
|
||||
The piece I worked was all the robotics parts: the boundary is at the API layer
|
||||
between the robot and the cat-detection service, accepting move-to commands
|
||||
over HTTP. This meant that I wore a lot of hats, from Rust and embedded linux
|
||||
to FPGA dev, electronics and mechanical engineering. It also meant that I had
|
||||
to make decisions to avoid as much hard complexity as possible in order to ship
|
||||
this much stuff on time.
|
||||
|
||||
This is the architecture diagram of the hardware components:
|
||||
|
||||
{% image(name="hw-arch-diagram.svg", colocated=true, process=false) %}
|
||||
Architecture diagram of the hardware. First commands come in via protobuf HTTP
|
||||
API, then they're processed by the meowzor-control daemon, which is attached to
|
||||
a Nios II microcontroller with shared memory and a mailbox. The Nios has a PIO
|
||||
connected to the stepper drivers.
|
||||
{% end %}
|
||||
|
||||
We use stepper motors because they are precise, pretty fast, cheap, and easy to
|
||||
integrate with.
|
||||
|
||||
The overall design is that `meowzor-control` receives position requests,
|
||||
generates step schedules, then gives them to the Nios II firmware to execute.
|
||||
|
||||
## Hardware
|
||||
|
||||
In my program we use a DE1-SoC Intel Cyclone V FPGA development board for
|
||||
pretty much everything, and everyone has one. This board has these relevant
|
||||
features:
|
||||
|
||||
* Cortex-A9 dual core hard processor
|
||||
* 1GB DDR3 memory
|
||||
* More FPGA than you need
|
||||
* Ethernet
|
||||
* GPIOs attached to the FPGA fabric
|
||||
|
||||
My goal was to make the hardware and firmware as simple as possible because
|
||||
they suck to work on, with the most basic FPGA system taking 6 minutes to
|
||||
synthesize with Intel Quartus. The less time I am waiting for a compiler, the
|
||||
more sane I will be. Firmware sucks slightly less to work on, but is also a
|
||||
[wreck of a mess][quartus-bad] due to Intel tools, and the Nios II only can run
|
||||
C/C++ due to the LLVM port being dead.
|
||||
|
||||
RISC-V would be viable if it weren't for the requirement to integrate nicely
|
||||
with the Intel tools. It looks like there's [some movement on making this
|
||||
work][riscv-demos], but I didn't want to take the risk on it. Intel itself has
|
||||
[made a RISC-V Nios processor][nios-v], but I was under the (apparently false?)
|
||||
impression that it was not available except in Quartus Pro licenses which we
|
||||
don't have.
|
||||
|
||||
[riscv-demos]: https://github.com/ARIES-Embedded/riscv-on-max10
|
||||
[nios-v]: https://www.intel.com/content/www/us/en/products/details/fpga/nios-processor/v.html
|
||||
|
||||
[quartus-bad]: https://jade.fyi/blog/quartus-elf2hex-and-misery/
|
||||
|
||||
Thus, what I did with the hardware is to try to shove everything nontrivial
|
||||
up-stack as much as possible. I used a soft core, the Nios II, to generate step
|
||||
signals, since it is easy to integrate with Quartus Platform Designer (Qsys) and
|
||||
thereby spend less energy on hardware. Platform Designer deals with all the annoying pieces of
|
||||
putting together a computer system such as address decoding and other kinds of
|
||||
wiring things up.
|
||||
|
||||
{% image(name="qsys.png", colocated=true) %}
|
||||
The main view of Platform Designer, listing components and showing connections
|
||||
between them, as well as memory mappings. There are two general groups of
|
||||
things: the hard processor and the soft core, which have distinct memory maps.
|
||||
The hard processor is attached to the shared memory and a mailbox component,
|
||||
and the soft core is attached to its own private memory, the shared memory, the
|
||||
mailbox, a timer, and a programmable IO block.
|
||||
{% end %}
|
||||
|
||||
In the end basically all of the hardware is just the reference design from the
|
||||
DE1-SoC materials and various integration in Platform Designer, which is a win
|
||||
because I mostly didn't have to debug it.
|
||||
|
||||
## Firmware
|
||||
|
||||
A mailbox in hardware is an inter-processor communication primitive: it takes a
|
||||
memory address and a command from the sending processor and interrupts the receiving processor when
|
||||
something new is received. The receiving processor can then take the address
|
||||
out of the mailbox, copy the memory out, then empty it for the next item.
|
||||
Optionally the sending processor may be interrupted to inform it of it being
|
||||
empty.
|
||||
|
||||
In the case of the Intel IP, the mailbox has a capacity of one item, and the
|
||||
interrupt to the receiving processor doesn't work, at least in my version of
|
||||
Quartus, so I just polled it (I may have screwed it up but I had bigger fish to
|
||||
fry than to spend more time debugging it; I have 100MHz to work with, so it
|
||||
does not matter one bit).
|
||||
|
||||
Mailboxes require that the receiving processor be able to read some kind of
|
||||
memory in common with the sending processor, since they only send one pointer.
|
||||
In this case I implemented it as shared memory, since I didn't want to write a
|
||||
Linux driver to deal with finding the physical pages I wanted to receive from
|
||||
or something like that.
|
||||
|
||||
The firmware for the Nios II accepts structures like this in shared memory when
|
||||
signaled by the mailbox:
|
||||
|
||||
```c
|
||||
typedef struct {
|
||||
CmdKind kind;
|
||||
Direction directions[N_MOTORS];
|
||||
uint16_t _pad;
|
||||
uint32_t delays[N_DELAYS];
|
||||
} Cmd;
|
||||
```
|
||||
|
||||
The delays are sent interleaved, with the motor ID in the top bit of them. As
|
||||
soon as the mailbox receives a `Cmd`, the main thread copies it into a
|
||||
(ring-buffer-based) queue in private memory and empties the mailbox. A timer
|
||||
ISR checks the queue and looks at the top item. If the item is done, it
|
||||
dequeues it. If not, it gets the next step in it, sets the direction, emits a
|
||||
step pulse, then sets the timer to the time of the next step.
|
||||
|
||||
## Software
|
||||
|
||||
### `meowzor-control`
|
||||
|
||||
### NixOS port
|
||||
|
||||
The port is [available here](https://github.com/lf-/de1-soc-nixos).
|
||||
|
||||
Well, this is sure burying a lede. I ported NixOS to the board and it was a
|
||||
*really really good idea* and saved me a load of time. It took about a week of
|
||||
work on and off. The motivation for the NixOS port was that the board vendor
|
||||
had last released a port of Ubuntu 18.04 and I would literally rather port a
|
||||
new OS than deal with old OS versions and lack of config management and
|
||||
inability to fix the image.
|
||||
|
||||
Then, there was no question of which OS I wanted to port: I wanted something I
|
||||
could rip everything out of easily and patch anything arbitrarily if needed.
|
||||
Theoretically I could have used Yocto but I looked at it briefly and it looked
|
||||
kinda like Nix But With Extra Ways To Have Incremental Build Mistakes, and more
|
||||
importantly I didn't want to learn it.
|
||||
|
||||
I read through the [Cyclone V GSRD][gsrd] (Golden Software Reference Design),
|
||||
which is an Intel port of Yocto to another board based on the Cyclone V, which
|
||||
should be very close to what I needed.
|
||||
|
||||
[gsrd]: https://www.rocketboards.org/foswiki/Documentation/CycloneVSoCGSRD
|
||||
|
||||
#### Background: Cyclone V SoC boot process
|
||||
|
||||
The Cyclone V SoC can boot in several different ways depending on how the
|
||||
`BSEL` pins are configured. This is broken out to an unpopulated DIP switch on
|
||||
the bottom of the DE1-SoC board, and the configured state is to boot off of an
|
||||
SD card.
|
||||
|
||||
When reset is deasserted, a boot ROM on the hard processor performs early
|
||||
hardware initialization, bringing up the CPU, and chain loading from some
|
||||
storage, in this case, a partition of a specific MBR type on the SD card.
|
||||
|
||||
See the [Cyclone V Hard Processor System Technical Reference Manual][hps-trm],
|
||||
appendix A, for more details on the early boot process.
|
||||
|
||||
[hps-trm]: https://www.intel.com/content/www/us/en/docs/programmable/683126/21-2/hard-processor-system-technical-reference.html
|
||||
|
||||
This partition contains the U-Boot SPL (second phase loader), which brings up
|
||||
the DDR3 main memory, serial port, and some other hardware, before chain
|
||||
loading into U-Boot itself.
|
||||
|
||||
The FPGA fabric configuration port is accessed in various ways depending on
|
||||
how the `MSEL` mode selection pins are set. On the DE1-SoC board, they are
|
||||
exposed as a DIP switch set on the bottom of the board. Note that surprisingly,
|
||||
`MSEL[3:0] = 4'b0000`, which you want, means *all the switches set to
|
||||
ON*. This setting corresponds to FPPx16 with no encryption (fast parallel
|
||||
programming), which is what works with U-Boot.
|
||||
|
||||
From U-Boot, the FPGA configuration image may be loaded into the
|
||||
configuration port. This can also be done through Linux at runtime using the
|
||||
[FPGA Region][fpga-region-dt] device tree entry.
|
||||
|
||||
[fpga-region-dt]: https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/fpga/fpga-region.txt
|
||||
|
||||
U-Boot will then chain load Linux, which NixOS supports well, so the boot
|
||||
process is very standard from there.
|
||||
|
||||
To get U-Boot to do so automatically, you need a snippet like the one below in
|
||||
your U-Boot Kconfig file. This will load a script if present, then enable the
|
||||
FPGA bridge, and boot Linux through the standard `extlinux.conf` mechanism.
|
||||
|
||||
```
|
||||
CONFIG_USE_BOOTCOMMAND=y
|
||||
CONFIG_BOOTCOMMAND="if ext4load mmc 0:2 ${scriptaddr} /boot/u-boot.scr; then source ${scriptaddr}; fi; bridge enable; run distro_bootcmd"
|
||||
```
|
||||
|
||||
#### The port
|
||||
|
||||
The first order of business was to get a kernel that worked. I looked at the
|
||||
GSRD, found the config I was supposed to use, then manually built a new kernel
|
||||
with the checkout of the kernel sources.
|
||||
|
||||
I then put that kernel into the minimal image from the board vendor and
|
||||
confirmed it booted. Success! Next, to build it with Nix.
|
||||
|
||||
Building a kernel with a custom config looks something like this in Nix ([full
|
||||
version][kernel.nix]):
|
||||
|
||||
[kernel.nix]: https://github.com/lf-/de1-soc-nixos/blob/main/kernel.nix
|
||||
|
||||
```nix
|
||||
{ stdenv, buildLinux, linuxKernel, ... } @ args:
|
||||
let base = buildLinux { ... };
|
||||
in linuxKernel.manualConfig {
|
||||
inherit stdenv;
|
||||
inherit (base) src version;
|
||||
configfile = ./socfpga_kconfig;
|
||||
allowImportFromDerivation = true;
|
||||
}
|
||||
```
|
||||
|
||||
It complained at build time about some missing options required by systemd, so
|
||||
I added those manually to the Kconfig in my checkout and copied it back.
|
||||
|
||||
Next, U-Boot. This was not a fun time but not because of Nix. I built U-Boot
|
||||
per the instructions on the GSRD guide, but using `socfpga_de1_soc_defconfig`
|
||||
instead of the one for the different board. I replaced the U-Boot in the same
|
||||
vendor image, and it would start, flash the transmit LED briefly, and not emit
|
||||
anything over the serial port. Concerning.
|
||||
|
||||
After googling it a lot I wound up finding a forum thread about getting U-Boot
|
||||
to work on the DE1-SoC, in which someone posted [a device tree patch][forum] to
|
||||
set the clock frequency of the UART. I applied this patch to my U-Boot
|
||||
development tree and, suddenly, console!! Rejoicing ensued before immediately
|
||||
sending the patch upstream so this never happens to anyone else.
|
||||
|
||||
[forum]: https://forum.rocketboards.org/t/cyclonev-programming-fpga-from-u-boot/2230/14
|
||||
|
||||
At this point I knew both my U-Boot and Linux kernel worked, so it was time to
|
||||
build a NixOS SD card image. This was one of the reasons I was excited to use
|
||||
NixOS for this project: if an SD card fails, I can just make a new image in 30
|
||||
seconds; the system image is totally disposable.
|
||||
|
||||
NixOS already has a [SD card image builder][sdimage-upstream] sort of
|
||||
supporting U-Boot, but it does such support by leaving a gap to put U-Boot in
|
||||
at the start of the disk after the fact. That wasn't quite satisfying enough
|
||||
for me because setting partition types and dd'ing things is effort and also I
|
||||
want to flash the image directly out of Nix.
|
||||
|
||||
I hacked this image builder up to [generate the correct partition
|
||||
table directly][sdimage-hacked] and also copy the U-Boot SPL image into place.
|
||||
|
||||
[sdimage-upstream]: https://github.com/nixos/nixpkgs/blob/0c67f190b188ba25fc087bfae33eedcc5235a762/nixos/modules/installer/sd-card/sd-image.nix
|
||||
|
||||
[sdimage-hacked]: https://github.com/lf-/de1-soc-nixos/blob/aa4ee306ab5a63e2e838d4ca7d219165c9695c31/sd-image.nix#L184-L192
|
||||
|
||||
At this point I was pretty confident that my NixOS system was going to just
|
||||
work when I booted it, since every part of the early boot was tested, so I just
|
||||
had a go and it worked. For ten seconds. Until it reset itself.
|
||||
|
||||
I was suspicious of power issues or some horrible crime being done to the
|
||||
hardware, so I removed the pieces surrounding the problematic time at boot such
|
||||
as resizing the root partition. This changed nothing and eventually I noticed
|
||||
it seemed to be based on *time* that the system was up. I got out a stop watch
|
||||
and it was a round number. Immediately I put two and two together and realized
|
||||
that Linux must not be correctly configured to pet the watchdog.
|
||||
|
||||
A quick comparison of the device trees used by the GSRD with the quite old ones
|
||||
used by the upstream DE1-SoC port in U-Boot yielded some slightly different
|
||||
watchdog configurations, so I just had a go and made them the same, added the
|
||||
patch to my U-Boot Nix build, and rebuilt the image:
|
||||
|
||||
```patch
|
||||
---
|
||||
arch/arm/dts/socfpga_cyclone5_de1_soc.dts | 4 ----
|
||||
1 file changed, 4 deletions(-)
|
||||
|
||||
diff --git a/arch/arm/dts/socfpga_cyclone5_de1_soc.dts b/arch/arm/dts/socfpga_cyclone5_de1_soc.dts
|
||||
index b71496bfb5..1cef1c2e8a 100644
|
||||
--- a/arch/arm/dts/socfpga_cyclone5_de1_soc.dts
|
||||
+++ b/arch/arm/dts/socfpga_cyclone5_de1_soc.dts
|
||||
@@ -78,7 +78,3 @@
|
||||
clock-frequency = <100000000>;
|
||||
u-boot,dm-pre-reloc;
|
||||
};
|
||||
-
|
||||
-&watchdog0 {
|
||||
- status = "disabled";
|
||||
-};
|
||||
--
|
||||
```
|
||||
|
||||
..... and it works:
|
||||
|
||||
|
||||
{% image(name="it-boots.png", colocated=true) %}
|
||||
Screenshot of a terminal showing the NixOS 23.05 prerelease NixOS booted to the
|
||||
login prompt on an armv7l-linux. Some lines above show "socfpga-dwmac" related
|
||||
ethernet messages.
|
||||
{% end %}
|
||||
BIN
content/posts/i-built-a-meowzor/it-boots.png
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|
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content/posts/i-built-a-meowzor/meowzor-board.jpg
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|
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content/posts/i-built-a-meowzor/qsys.png
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content/posts/i-built-a-meowzor/qsys.png
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|
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|
|
@ -61,6 +61,7 @@
|
|||
cabal-install
|
||||
] ++ (with pkgs; [
|
||||
sqlite
|
||||
pre-commit
|
||||
]);
|
||||
# Change the prompt to show that you are in a devShell
|
||||
# shellHook = "export PS1='\\e[1;34mdev > \\e[0m'";
|
||||
|
|
|
|||
|
|
@ -1,21 +1,28 @@
|
|||
{%- import "macros/colocated_asset.html" as colocated_asset -%}
|
||||
|
||||
{%- macro image(name, alt, colocated, height) -%}
|
||||
{%- macro image(name, alt, colocated, height, process) -%}
|
||||
{%- set name_sanitized = name | replace(from=".", to="-") | replace(from="/", to="-") -%}
|
||||
{%- set image_id = "image" ~ name_sanitized -%}
|
||||
|
||||
{%- if colocated == true -%}
|
||||
{%- set image_path = colocated_asset::colocated_asset(path=name) -%}
|
||||
{%- set image_url = name -%}
|
||||
{%- set image_url = colocated_asset::colocated_asset(path=name, get_url=true) -%}
|
||||
{%- else -%}
|
||||
{%- set image_path = "/static/images/" ~ name -%}
|
||||
{%- set image_url = get_url(path=image_path) -%}
|
||||
{%- endif -%}
|
||||
|
||||
{%- set image = resize_image(path=image_path, width=800, height=height, op="fit") -%}
|
||||
{%- if process -%}
|
||||
{%- set image = resize_image(path=image_path, width=800, height=height, op="fit") -%}
|
||||
{# because tera doesn't have object literals we need to deconstruct the object here so the other case is compatible #}
|
||||
{%- set processed_image_url = image.url -%}
|
||||
{%- else -%}
|
||||
{%- set image = colocated_asset::colocated_asset(path=image_path, get_url=true) | trim -%}
|
||||
{%- set processed_image_url = image_url -%}
|
||||
{%- endif -%}
|
||||
<div class="image">
|
||||
<a href="{{ image_url }}">
|
||||
<img src="{{ image.url }}"
|
||||
<img src="{{ processed_image_url }}"
|
||||
alt="{{ alt }}"
|
||||
title="{{ alt }}"
|
||||
{% if label %}
|
||||
|
|
|
|||
|
|
@ -4,6 +4,7 @@
|
|||
name=name,
|
||||
colocated=colocated | default(value=false),
|
||||
alt=alt | default(value=body),
|
||||
height=height | default(value=600)
|
||||
height=height | default(value=600),
|
||||
process=process | default(value=true)
|
||||
) }}
|
||||
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue