Author Archives: Liz Upton

Plague at Pi Towers

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Alex, Helen and I are all in our respective beds today with the plague. So your usual blog fodder won’t get served up today because none of us can look at a monitor for more than thirty seconds at a trot: instead I’m going to ask you to come up with some content for us. Let us know in the comments what you think we should be blogging about next, and also if you have any top sinus remedies.

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VC4 and V3D OpenGL drivers for Raspberry Pi: an update

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Here’s an update from Iago Toral of Igalia on development of the open source VC4 and V3D OpenGL drivers used by Raspberry Pi.

Some of you may already know that Eric Anholt, the original developer of the open source VC4 and V3D OpenGL drivers used by Raspberry Pi, is no longer actively developing these drivers and a team from Igalia has stepped in to continue his work. My name is Iago Toral (itoral), and together with my colleagues Alejandro Piñeiro (apinheiro) and José Casanova (chema), we have been hard at work learning about the V3D GPU hardware and Eric’s driver design over the past few months.

Learning a new GPU is a lot of work, but I think we have been making good progress and in this post we would like to share with the community some of our recent contributions to the driver and some of the plans we have for the future.

But before we go into the technical details of what we have been up to, I would like to give some context about the GPU hardware and current driver status for Raspberry Pi 4, which is where we have been focusing our efforts.

The GPU bundled with Raspberry Pi 4 is a VideoCore VI capable of OpenGL ES 3.2, a significant step above the VideoCore IV present in Raspberry Pi 3 which could only do OpenGL ES 2.0. Despite the fact that both GPU models belong in Broadcom’s VideoCore family, they have quite significant architectural differences, so we also have two separate OpenGL driver implementations. Unfortunately, as you may have guessed, this also means that driver work on one GPU won’t be directly useful for the other, and that any new feature development that we do for the Raspberry Pi 4 driver stack won’t naturally transport to Raspberry Pi 3.

The driver code for both GPU models is available in the Mesa upstream repository. The codename for the VideoCore IV driver is VC4, and the codename for the VideoCore VI driver is V3D. There are no downstream repositories – all development happens directly upstream, which has a number of benefits for end users:

  1. It is relatively easy for the more adventurous users to experiment with development builds of the driver.
  2. It is fairly simple to follow development activities by tracking merge requests with the V3D and VC4 labels.

At present, the V3D driver exposes OpenGL ES 3.0 and OpenGL 2.1. As I mentioned above, the VideoCore VI GPU can do OpenGL ES 3.2, but it can’t do OpenGL 3.0, so future feature work will focus on OpenGL ES.

Okay, so with that introduction out of the way, let’s now go into the nitty-gritty of what we have been working on as we ramped up over the last few months:

Disclaimer: I won’t detail here everything we have been doing because then this would become a long and boring changelog list; instead I will try to summarize the areas where we put more effort and the benefits that the work should bring. For those interested in the full list of changes, you can always go to the upstream Mesa repository and scan it for commits with Igalia authorship and the v3d tag.

First we have the shader compiler, where we implemented a bunch of optimizations that should be producing better (faster) code for many shader workloads. This involved work at the NIR level, the lower-level IR specific to V3D, and the assembly instruction scheduler. The shader-db graph below shows how the shader compiler has evolved over the last few months. It should be noted here that one of the benefits of working within the Mesa ecosystem is that we get a lot of shader optimization work done by other Mesa contributors, since some parts of the compiler stack are shared across multiple drivers.

Bar chart with y-axis range from -12.00% to +2.00%. It is annotated, "Lower is better except for Threads". There are four bars: Instructions (about -4.75%); Threads (about 0.25%); Uniforms (about -11.00%); and Splits (about 0.50%).

Evolution of the shader compiler (June vs present)

Another area where we have done significant work is transform feedback. Here, we fixed some relevant flushing bugs that could cause transform feedback results to not be visible to applications after rendering. We also optimized the transform feedback process to better use the hardware for in-pipeline synchronization of transform feedback workloads without having to always resort to external job flushing, which should be better for performance. Finally, we also provided a better implementation for transform feedback primitive count queries that makes better use of the GPU (the previous implementation handled all this on the CPU side), which is also correct at handling overflow of the transform feedback buffers (there was no overflow handling previously).

We also implemented support for OpenGL Logic Operations, an OpenGL 2.0 feature that was somehow missing in the V3D driver. This was responsible for this bug, since, as it turns out, the default LibreOffice theme in Raspbian was triggering a path in Glamor that relied on this feature to render the cursor. Although Raspbian has since been updated to use a different theme, we made sure to implement this feature and verify that the bug is now fixed for the original theme as well.

Fixing Piglit and CTS test failures has been another focus of our work in these initial months, trying to get us closer to driver conformance. You can check the graph below showcasing Piglit test results to have a quick view at how things have evolved over the last few months. This work includes a relevant bug fix for a rather annoying bug in the way the kernel driver was handling L2 cache invalidation that could lead to GPU hangs. If you have observed any messages from the kernel warning about write violations (maybe accompanied by GPU hangs), those should now be fixed in the kernel driver. This fix goes along with a user-space fix to go that should be merged soon in the upstream V3D driver.

A bar chart with y-axis ranging from 0 to 16000. There are three groups of bars: "June (master)"; "Present (master)"; Present (GLES 3.1)". Each group has three bars: Pass; Fail; Skip. Passes are higher in the "Present (master)" and "Present (GLES 3.1)" groups of bars than in the "June (master)" group, and skips and fails are lower.

Evolution of Piglit test results (June vs present)

A a curiosity, here is a picture of our own little continuous integration system that we use to run regression tests both regularly and before submitting code for review.

Ten Raspberry Pis with small black fans, most of them in colourful Pimoroni Pibow open cases, in a nest of cables and labels

Our continuous integration system

The other big piece of work we have been tackling, and that we are very excited about, is OpenGL ES 3.1, which will bring Compute Shaders to Raspberry Pi 4! Credit for this goes to Eric Anholt, who did all the implementation work before leaving – he just never got to the point where it was ready to be merged, so we have picked up Eric’s original work, rebased it, and worked on bug fixes to have a fully conformant implementation. We are currently hard at work squashing the last few bugs exposed by the Khronos Conformance Test Suite and we hope to be ready to merge this functionality in the next major Mesa release, so look forward to it!

Compute Shaders is a really cool feature but it won’t be the last. I’d like to end this post with a small note on another important large feature that is currently in early stages of development: Geometry Shaders, which will bring the V3D driver one step closer to exposing a full programmable 3D pipeline – so look forward to that as well!

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Eight years, 2000 blog posts

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Today’s a bit of a milestone for us: this is the 2000th post on this blog.

Why does a computer company have a blog? When did it start, who writes it, and where does the content come from? And don’t you have sore fingers? All of these are good questions: I’m here to answer them for you.

The first ever Raspberry Pi blog post

Marital circumstances being what they are, I had a front-row view of everything that was going on at Raspberry Pi, right from the original conversations that kicked the project off in 2009. In 2011, when development was still being done on Eben’s and my kitchen table, we met with sudden and slightly alarming fame when Rory Cellan Jones from the BBC shot a short video of a prototype Raspberry Pi and blogged about it – his post went viral. I was working as a freelance journalist and editor at the time, but realised that we weren’t going to get a better chance to kickstart a community, so I dropped my freelance work and came to work full-time for Raspberry Pi.

Setting up an instantiation of WordPress so we could talk to all Rory’s readers, each of whom decided we’d promised we’d make them a $25 computer, was one of the first orders of business. We could use the WordPress site to announce news, and to run a sort of devlog, which is what became this blog; back then, many of our blog posts were about the development of the original Raspberry Pi.

It was a lovely time to be writing about what we do, because we could be very open about the development process and how we were moving towards launch in a way that sadly, is closed to us today. (If we’d blogged about the development of Raspberry Pi 3 in the detail we’d blogged about Raspberry Pi 1, we’d not only have been handing sensitive and helpful commercial information to the large number of competitor organisations that have sprung up like mushrooms since that original launch; but you’d also all have stopped buying Pi 2 in the run-up, starving us of the revenue we need to do the development work.)

Once Raspberry Pis started making their way into people’s hands in early 2012, I realised there was something else that it was important to share: news about what new users were doing with their Pis. And I will never, ever stop being shocked at the applications of Raspberry Pi that you come up with. Favourites from over the years? The paludarium’s still right up there (no, I didn’t know what a paludarium was either when I found out about it); the cucumber sorter’s brilliant; and the home-brew artificial pancreas blows my mind. I’ve a particular soft spot for musical projects (which I wish you guys would comment on a bit more so I had an excuse to write about more of them).

As we’ve grown, my job has grown too, so I don’t write all the posts here like I used to. I oversee press, communications, marketing and PR for Raspberry Pi Trading now, working with a team of writers, editors, designers, illustrators, photographers, videographers and managers – it’s very different from the days when the office was that kitchen table. Alex Bate, our magisterial Head of Social Media, now writes a lot of what you see on this blog, but it’s always a good day for me when I have time to pitch in and write a post.

I’d forgotten some of the early stuff before looking at 2011’s blog posts to jog my memory as I wrote today’s. What were we thinking when we decided to ship without GPIO pins soldered on? (Happily for the project and for the 25,000,000 Pi owners all over the world in 2019, we changed our minds before we finally launched.) Just how many days in aggregate did I spend stuffing envelopes with stickers at £1 a throw to raise some early funds to get the first PCBs made? (I still have nightmares about the paper cuts.) And every time I think I’m having a bad day, I need to remember that this thing happened, and yet everything was OK again in the end. (The backs of my hands have gone all prickly just thinking about it.) Now I think about it, the Xenon Death Flash happened too. We also survived that.

At the bottom of it all, this blog has always been about community. It’s about sharing what we do, what you do, and making links between people all over the world who have this little machine in common. The work you do telling people about Raspberry Pi, putting it into your own projects, and supporting us by buying the product doesn’t just help us make hardware: every penny we make funds the Raspberry Pi Foundation’s charitable work, helps kids on every continent to learn the skills they need to make their own futures better, and, we think, makes the world a better place. So thank you. As long as you keep reading, we’ll keep writing.

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Literature dispenser

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There are many things I do not know about Argentina. Until today, one of them was this: if you’re in an Argentinian bank, you may not use electronic devices. That includes phones and e-readers like the Kindle (and I can’t be the only person here who is pretty much surgically attached to their Kindle).

Enter the literature dispenser.

Roni Bandini, an Argentinian author, found himself twiddling his thumbs in a Buenos Aires bank queue, and thought that perhaps the 50 other people he could see in the same situation might benefit from a little distraction. How about a machine, owned by the bank, that could furnish you with one of a curated selection of short stories at the touch of a button? The short stories bit was easy: he writes them for a living.

Expendedor de literatura en tickets (invento argentino)

Expendedor de literatura en tickets desarrollado por @ronibandini Versión 2 Elementos utilizados para su fabricación: Raspberry Pi Thermal Printer LCD Display 16×2 Custom 3d Printed Case Más información en https://medium.com/@Bandini

He chose a Raspberry Pi because there are so many libraries for thermal printers and LCD displays available (and because it’s tiny, and you can fit a heck of a lot of short stories on an SD card these days).

Roni says:

This project was “trial and error” in many aspects. I had troubles with power source amperage due to thermal printer requirements, conflicts with previous software running in the Raspberry – since the same one was used for other projects – and I had to write some routines to avoid words being split due to ticket width. Since the machine could be working for 12 hours in a row, I have added a small 5v cooling fan in the back.

He built a wooden prototype, and was helped out by Z-lab, a small, local 3d print design studio, with permanent casing (which is rather lovely).

literature dispenser

The UI’s very simple: press the green button, be rewarded with a short story, printed to order on a till strip. We’d love to see businesses use these in real life (and we’re thinking one of these would be a lovely addition to the Pi Towers lobby, to help soothe anxious interview candidates). Thanks Roni – I’m off to try to find some of your work in translation, and we’re all agreed that we’re very grateful for internet banking.

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We have the plague

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Apologies to our daily visitors (we love you guys); we don’t have a proper blog post for you today because we’re all really ill. (I have food poisoning, Helen is coughing up goo and can barely speak or breathe, and Alex is being sick.)

You’ve got a day until Halloween; if you’re looking for inspiration, we’ve got several years of archived spooky project posts for you to check out. And now, if you’ll excuse me, I’m going to go and have a little lie down.

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Autonomous drones (only slightly flammable)

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I had an email a little while ago, which opened: “I don’t know if you remember me, but…”

As it happens, I remembered Andy Baker very well, in large part because an indoor autonomous drone demo he ran at a Raspberry Pi birthday party a couple of years ago ACTUALLY CAUGHT FIRE. Here’s a refresher.

Raspberry Pi Party Autonomous drone demo + fire

At the Raspberry Pi IV party and there is a great demo of an Autonomous drone which is very impressive with only using a Pi. However it caught on fire. But i believe it does actually work.

We’ve been very careful since then to make sure that speakers are always accompanied by a fire extinguisher.

I love stories like Andy’s. He started working with the Raspberry Pi shortly after our first release in 2012, and had absolutely no experience with drones or programming them; there’s nothing more interesting than watching someone go from a standing start to something really impressive. It’s been a couple of years since we were last in touch, but Andy mailed me last week to let me know he’s just completed his piDrone project, after years of development. I thought you’d like to hear about it too. Over to Andy!

Building an autonomous drone from scratch

I suffer from “terminal boredom syndrome”; I always need a challenging hobby to keep me sane. In 2012, the Raspberry Pi was launched just as my previous hobby had come to an end. After six months of playing (including a Raspberry Pi version of a BBC Micro Turtle robot I did at school 30+ years ago), I was looking for something really challenging. DIY drones were emerging, so I set out making one with a Raspberry Pi and Python, from absolute ignorance but loads of motivation.  Six years later, with only one fire (at the Raspberry Pi 4th Birthday Party, no less!), the job is done.

Here’s smaller Zoë, larger Hermione and their remote-controller, Ivy:

Zoë (as in “Ball”), the smallest drone, is based on a Pi ZeroW, supporting preset- and manual-flight controls. Hermione (as in “Granger”) is a Pi3 drone, supporting the above along with GPS and obstacle-avoidance.

Penelope (as in “Pitstop”), not shown above, is a B3+ with mix of the two above.

Development history

It probably took four years(!) to get the drone to simply hover stably for more than a few seconds. For example, the accelerometer (IMU) tells gravity and acceleration in 3D; and from sum math(s), angles, speed and distance. But IMU output is very noisy. It drifts with temperature, and because gravity is huge compared to the propeller changes, it doesn’t take long before the calculated speed and distance values drift significantly. It took a lot of time, experimentation and guesswork to get accelerometer, gyrometer, ground-facing LiDAR and a Raspberry Pi camera to work together to get a stable hover for minutes rather than seconds. And during that experimentation, there were plenty of crashes: replacement parts were needed many many times! However, with a sixty-second stable hover finally working, adding cool features like GPS tracking, object avoidance and human control were trivial in comparison.

GNSS waypoint tracked successfully!

See http://blog.pistuffing.co.uk/whoohoo/

Obstruction avoidance test 2 – PASSED!!!!!

Details at http://pidrone.io/posts/obstruction-avoidance-test-2-passed/

Human control (iPhone)

See http://pidrone.io/posts/human-i-am-human/

In passing, I’m a co-founder and assistant at the Cotswold Raspberry Jam (cotswoldjam.org). I’m hoping to take Zoë to the next event on September 15th – tickets are free – and there’s so much more learn, interact and play with beyond the piDrone.

Finally, a few years ago, my goal became getting the piDrone exploring a maze: all but minor tweaks are now in places. Sadly, piDrone battery power for exploring a large maze currently doesn’t exist. Perhaps my next project will be designing a nuclear-fusion battery pack?  Deuterium oxide (heavy water) is surprisingly cheap, it seems…

More resources

If you want to learn more, there’s years of development on Andy’s blog at http://pidrone.io, and he’s made considerable documentation available at GitHub if you want to explore things further after this blog post. Thanks Andy!

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