I have recently started experimenting on the intersection of software and hardware, by playing with the GPIO pins on a Raspberry Pi, with software written in Go. Mostly everything is working out well so far, but there's one thing I can't really wrap my head around yet and that's how to efficiently do edge detection on an input pin and trigger code accordingly.
I am using the following library (rpio) as an abstraction over the raw GPIO layer and it contains functions to start watching for edge events and checking if an edge event occurred. Other libraries seem to employ similar patterns. I can't imagine it's actually intended to be completely poll-based though. Granted I'm new to this, but I'm not new to software development and polling for change seems both inefficient and slow. I could write a simple loop polling for the change maybe a hundred times per second, but it feels wrong. Especially when watching more pins than one.
Therefore I am fairly confident I'm missing or misreading something and I wonder if you can point me into a better direction.
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I’m a college student and I’m trying to build an underwater robot with my team.
We plan to use stm32 and RPi. We will put our controller on stm32 and high-level algorithm (like path planning, object detection…) on Rpi. The reason we design it this way is that the controller needs to be calculated fast and high-level algorithms need more overhead.
But later I found out there is tons of package on ROS that support IMU and other attitude sensors. Therefore, I assume many people might build their controller on a board that can run ROS such as RPi.
As far as I know, RPi is slower than stm32 and has less port to connect to sensor and motor which makes me think that Rpi is not a desired place to run a controller.
So I’m wondering if I design it all wrong?
Robot application could vary so much, the suitable structure shall be very much according to use case, so it is difficult to have a standard answer, I just share my thoughts for your reference.
In general, I think Linux SBC(e.g. RPi) + MCU Controller(e.g. stm32/esp32) is a good solution for many use cases. I personally use RPi + ESP32 for a few robot designs, the reason is,
Linux is not a good realtime OS, MCU is good at handling time critical tasks, like motor control, IMU filtering;
Some protection mechnism need to be reliable even when central "brain" hang or whole system running into low voltage;
MCU is cheaper, smaller and flexible to distribute to any parts inside robot, it also helps our modularized design thinking;
Many new MCU is actually powerful enough to handle sophisticated tasks and could offload a lot from the central CPU;
I'm a bit stumped.
I have a fairly large verilog module that I've tested in Simulation (iSim) and it functions as I want. Now I've hooked up it up in real life to another device using SPI, and some stuff works, and some stuff doesn't.
For example,
I can send a value using command A, and verify that the right value was received using command B. Works no problem.
But if I send a value using command C, I cannot verify that it was received using command D. In simulation it works fine, so I feel I can't really gain anything from simulating any more.
I have looked at the signals on a logic analyzer, and the controller device (not my design) sends the right messages. When I issue command B, I can see the return values correct from my device (I know SPI works anyways). I don't know whether C or D work correctly. D just returns 0s, so maybe C didn't work in the first place. There is no way to step through Verilog, and this module is packaged as IP for Vivado.
Here are two screenshots. First is simulation (I send 5, then 2, then I expect it to return 4 on the next send, which it does; followed by zeros).
Here is what I get in reality (the first two bytes don't matter, 5 is a left over from previously sent value):
Here is a command (B) that works in returning a correct value (it responds to the 0x01 being sent):
Does anyone have any advice for debugging this? I have literally no idea how to proceed.
I can't really reproduce this behaviour in simulation.
Since you are synthesizing to an FPGA, you have a few more options on how to debug your synthesized, on-chip design. As you are using Vivado, you can use ChipScope to look at any signal in your system; allowing you to view a waveform of that signal over time just as you would in simulation (though more restricted). By including the ChipScope IPs into your synthesis, you can sent waveform data back to the Vivaod software which will display a waveform of your selected signals to help you see whats going on inside the FPGA as the system runs. (Note, if you were using Altera's stuff, you can use their equivalent called SignalTap; its pretty much the same thing)
There are numerous tutorial online on how to incorporate and run ChipScope, heres one from the Xilinx website:
http://www.xilinx.com/support/documentation/sw_manuals/xilinx2012_4/ug936-vivado-tutorial-programming-debugging.pdf
Many other use ISE, but the steps are very similar as both typically involve using the coregen tool (though I think you can also add ChipScope via synthesis flow, so there are multiple options on how to incorporate it into your design).
Once on the FPGA, you have access to what is effectively an internal logic analyzer. Note that it does take up some LEs on the FPGA and can take up a fair amount of block RAM depending on how many samples you want to take out your signals.
Tim's answer provides a good description of how to deal with on-chip debugging if you are designing purely for ASIC; so see his answer if you want more information about standard, non-FPGA debugging solutions.
In cases like this you might want to think about adding additional logic which is used just for debugging. ('Design for debug') is a common term used for thinking about this kind of logic.
So you have one chip interface (SPI), which you don't know if it works correctly. Since it seems not to be working, you can't trust debugging over this interface, because if you get an odd result you can't determine what it means.
Since you're working on an FPGA, are there any other interfaces other than SPI which you can get working correctly? Maybe 7-segment display, LEDs, JTAG, VGA, etc?
Try to think of other creative ways to get data out of your chip that don't require the SPI interface.
If you have 4 LEDs, A through D, can you light up each LED for 1 second each time a command of that type is received?
Can you have a 7-seg display the current state of your SPI receiver's state machine, or have it indicate certain error codes if some unknown command is received?
Can you draw over VGA to a monitor a binary sequence of the incoming SPI bitstream?
Once you can start narrowing down with data what is actually happening inside your hardware, you can narrowing the problem space to go inspect for possible problems.
There are multiple reasons why code that runs ok in RTL simulation behaves differently in the FPGA. It is important to consider all possibilities. Chipscope suggested above is definitely a step in right direction and it could give you hint, where to look further. These reasons could be:
The FPGA implementation flow was not executed properly. Did you have right timing constraints, were they met during implementation, especially P&R phase, pin placements, I/O properties, right clock properties. Usually you can find hints inspecting FPGA implementation reports. This is a tedious part, but needed sometimes. Incorrect implementation flow can also result in FPGA implementations that work or don't depending on the run or small unrelated changes (seen this problem many times!).
RTL/netlist discrepancies, e.g. due to incorrect usage `ifdef within design or during synthesis phase, selecting incorrect file for synthesis or the same verily module defined in multiple places. Often, the hint could be found by inspecting removed flop list or synthesis warnings.
Discrepancy between RTL simulation and board environment. They could be external like the clock/data alignment on the interface, but also internal: improper CDC, not handling clock or reset tree delays properly. Note, that X-propagation and CDC is not handled properly in RTL, unless you code in a certain way. Problems with those could be often only seen in netlist simulation environment.
Lastly, the FPGA board problems, like faulty clock source or power supply, heat can also be at fault. They worth checking, but I'd leave those as a last resource. Some folks have a dedicated board/FPGA test design proven to work on the good board that would catch some of those problems.
As a final note, the biggest return is given by investing in simulation environment. Some folks think that since FPGA can be debugged with chipscope and reprogrammed quickly, there is no need in good simulation environment. It probably depends on the size of the project, but my experience is that for most of modern FPGA projects the good simulation environment saves a lot of time spent in the lab looking through chipscope and logic analyzers captures.
I may be a bit in over my head here, but if you never try new things - you'll never learn I suppose. I'm working with some multi-touch stuff and have built myself a small but functional GUI library. Up until now I've been used boosts Signals2 library to have my detected gestures be distributed to all active GUI elements (whether on screen or not). I'm a big fan of avoiding pre-mature optimization, so things have been honky-dory until now.
I've used vs2013's profiler to find out that when the user goes touch crazy (the device supports up to 41 simultaneous touches), then my system grinds to a halt, and Signals2 is the culprit. Keep in mind that each touch can trigger a number of Gestures which are all communicated to every GUI element that have registered to interact with this type of Gesture.
Now there are a number of ways to deal with this bottleneck:
Have GUI elements work more cleverly and disconnect them when they're off-screen.
Optimize the signals/slots system so the calls are resolved faster.
Prioritization of events.
I'm not a big fan of ever having to deal with 3 - if avoidable - as it'll directly impact the responsiveness of my application. Nr. 1 should probably be implemented, but I'm more interested in getting to Nr. 2 first.
I don't really need any big fancy stuff. The Signals/Slots system I'd need really only needs to do the core emission stuff along with these 2 feature:
Slots must be able to return a value ending the emission - effectively cancelling any subsequent handling of a signal.
Slots must be order-able - and fairly efficient at this. GUI elements that are interacted with will pop-up above others, so this type of change in order is bound to happen quite often.
I stumbled across this really interesting implementation
https://testbit.eu/2013/cpp11-signal-system-performance/
which seems to have everything except the 'ordering' I need. I've only looked over the code once, and it does seem a little intimidating. If I were to try and add ordering capabilities, I'd prefer not to change too much stuff around if necessary. Does anyone have experience with this stuff? I'm fairly certain that a linked list is not optimal for constant removal and insertion, but then again, it probably needs to be optimized the most for constant emission calls.
Any thoughts are most welcome!
--- Update ---
I've spend a little time adding the features I needed to the code put into the public domain above and pasted the complete (and somewhat hacky version) here:
SimpleSignal with added features
In short, I've added:
Blockable Connections (Implemented via simple IF statement)
Depth/Order parameter (Linear-search insertion)
With those additions, keep in mind it has these current issues:
Blocked connections are simply skipped, not actively removed from the data-structure, so having a lot of blocked connections will affect run-time performance.
Depth is only maintained during insertion. So if you'd like to change the depth you'll have to disconnect and reconnect your slot.
Since the SignalLink interface has become exposed (as a result of my block implementation), it's less safe from a user perspective. It's way easier for you to shoot yourself in the foot with this version by messing with existing references and pointers.
This implementation hasn't been as thoroughly tested as the original I'm sure. I did try out the new functionality a bit. User beware.
I'm starting game development, but I really want to avoid hacking together a step-by-step game. I'm thinking, what's a good system for handling all that goes on?
For example, I thought of making a menu class, that contains an array of objects for buttons in the menu, and then every game loop call update() on the menu, which in turn calls update() on all the buttons, passing user input and such along the way. Is this a good way to do it?
I'm trying to find structural techniques past the game loop, any advice would be appreciated. Thanks!
(BTW I'm using c++)
This question is not that trivial, but let me try to give you a really simple answer. You need at minimum a core architecture where you can register several engines. Take a deep look into state machines and several software patterns. There have been really greate game dev books like the Game Programming Gems. Start reading an older book from André LaMothe. Read source code ie. from Half Life 2 that could be downloaded at some places.
It sure depends on the environment, C++ is best and could be the fastest way to write games but would you like to use DirectX or OpenGL, do you need Audio and advanced input? Do you want to start with the older WinApi? Nevertheless it always starts in a single point, the main loop. There your state machine should be initialized and all resource managers need to be set up. For graphical objects you need to think about a low level init, update, draw, release and destroy cycle. UI is built up on Graphics, Input and other parts. Don't start writing your own UI or you need to spend the next 2 years with it. You need a relational game model that describes the world you want to create.
To be honest, read a lot about patterns (like mvc), state machines, gpu pipelines and framework design. Read a lot of code from very talented people that open sourced it for us:)
By the way, what is a step by step game?
I have been asked to investigate porting Wii games and some (Sony) PSOne games to OpenGL ES (can you guess what platform?).
I have never undertaken a game port like this before (and will be hiring someone to do it) but I'd like to understand the process.
Does the Wii use OpenGL? If not what does it use and how easy is it to port to OpenGL / OpenGL ES?
Are there any resources/books/blogs that will help me in understanding the process?
Will my company have to become an official Wii developer? If so where do I start that process?
Porting from the Wii or the PSOne is a complex and involved task that can be broken down into multiple separate engineering efforts working in parallel to produce a working end product. The best possible thing you can do before moving to the target hardware is to compartmentalize all of the non-portable code while ensuring that the game continues to run as expected. When you commit to moving to the new platform, your effort switches to reimplementing the non-portable compartmentalized parts.
So, to answer your question, yes, you will need to become or work with a Sony and Nintendo licensed developer in order to take this approach. In the case of Sony, I don't even know if they offer a PSOne development program anymore which presents issues. Your Sony account rep can help clarify.
The major subsystems that are likely to be the focus of your porting effort are:
Rendering Graphics code contains fundamental assumptions about the hardware it is being run on in order to perform optimally. API-level compatibility is superficial compatibility and does not get you as much as you may hope it does. Plan on finding the entry point to the renderer and determining what data you need to render a scene and rewriting all the render code from there for your target hardware.
Game Saving Game state serialization and archival will need to be separated out. Older games often fwrite() structs with #pragma packed fields. Is that still going to work for you?
Networking Wii games write to high level services that are unavailable on your target hardware. At the low level, sockets are still sockets. What network services do your Wii games rely on?
Controls From where you are coming from to where you are going, anything short of a full redesign or reimagining of input will result in poor reviews of the software.
Memory Management Console games often make fundamental assumptions about the rate the system software returns memory from the heap, how much fragmentation it will cause and the duration the game needs to operate under these conditions. These memory management assumptions are obsolete on the new platform. It is wise to write your own memory manager that provides a cushion from the operating system. Also, console games compiled for release are stripped of most error handling and don't gracefully handle running out of memory-- just a heads up.
Content Your bottleneck will be system memory. Can you fit the necessary assets into memory? With textures, you can reduce mip where necessary and with graphics hardware timing, you can pull in the far clipping plane. With assets resident in memory, you may need a technical artist to go through and reduce the face density of your models or an animation programmer to implement a more size-friendly animation codec. This is very game specific.
You also run into the standard set of problems with things like bit compatibility (though the Wii and PSOne are both 32-bit), compiler idiosyncrasies, build script incompatibilities and proprietary compiler extensions.
Games are relatively challenging to test. A good rule of thumb is you want to have enough testers on your team to run through the game in a maximum of two days, covering all major aspects of play. In games that take a long time to beat (RPGs with 30+ hours of gameplay), your testing team needs to be quite large to offer full coverage. Because you are just doing a port, you can come up with a testing plan that maximizes coverage of your new code without having a testing team punch every wall in your game to make sure it (still) has clipping. The game shipped once.
Becoming a licensed developer requires you to apply. The turnaround time, from experience, is not good. Generally speaking, priority is given to studios with shipped titles and organized offices with reasonably good security and the ability to buy the (relatively) expensive development kits. You may be better off working with a licensed developer if you do not meet these criteria.
Console and game development is challenging for people already experienced in it. There is no book that covers it all. My recommendation is to attempt to recruit an expert who has experience shipping titles in a position of systems or engine programmer. What types of programmers and skillsets exist in games is a whole different question for Stack, though.
Games consoles don't use OpenGL but their own, custom libraries. The main reason is that they are pretty slow and have little RAM. So you need to squeeze out every drop of performance you can get. And that means: Custom code. Usually, you get a framework with the developer kit which gets you started and then, you build your code from that. Eventually, you'll start replacing parts from the developer kit with your own special code to get all the speed and special effects you need.
There is a reason why PSOne games are so ugly on the PS3 despite the fact that the developers have access to the sources: Revenue just doesn't justify to touch the code.
Which is one reason why game development is so expensive: Every game is (more or less) a completely new product. Sometimes, game companies can reuse a bit of code from the last version but more often than not, they have to develop everything again. They also don't talk much with each other.
In recent years, kits have become more complex and powerful and you can get complete game engines (with all kinds of effects and 3D support) but each engine is a completely different kind of beast, so you can't even copy code from engine A to B.
Today, media content (video, audio and render sequences) are so expensive that the actual game engine is often a minor detail, so this isn't going to change any time soon.
Net result: If you want to port a game, write an emulator for the hardware (which is usually pretty simple and allows you to run all kinds of games).
[EDIT] To develop software for the Wii, see here: http://www.warioworld.com/
For a Wii emulator, see http://wiiemulator.net/
I ported a couple of games, when I was a new game programmer, from working with one version of our engine to a newer version (where backwards compatibility was neither ignored nor pursued). Even copying (and possibly renaming) the files and placing them in a home in the new project was a bit of work. Following that, the procedure was:
recompile
fix many of the hundreds of errors [in many places, with the same error occurring over and over again]
and
"wire up" calls from the new game engine to the appropriate calls in the old code
"wire up" function calls from the old code into the new game engine
deal with other oddities (ex. in the old game engine, the 2d game would "swizzle" textures itself; in the new version, the engine did it (on specific platforms))
and, while I don't recall this clearly, it was probably mixed in with a bunch of #ifdeffing out portions of code so the thing would actually compile, and possibly creating function stubs to be filled in later.
As I recall, it was three or four days until I had something that compiled. (But, it did help when we ported other games from the old version to the new one!)
The magnitude of the task will come down to what the code you are getting is like. If it has generic 3D calls that you can intercept -- add a thunking layer to -- then you are in business. It depends on the level of abstraction in the code. If it is well-behaved and has things like "RenderModel" and "RenderWorld" calls, you can replace those functions, and even the structures that they work with. If drawing is occurring all over the place, and calls are more like "Draw Polygon" and "Draw Line" or "Draw using this highly optimised data structure", then you are likely in for a long slog.
You shouldn't need a Wii dev kit. Sometimes it is nice to verify that the code you are given does indeed compile in the original environment (and matches the shipping code!), but sometimes you can just take it on faith and make it work in its new environment.
Lastly, I don't think the Wii uses OpenGL, and I really don't know where to point you for further help.
What you may want to do is to start with designing the architecture of the game, write up a detailed specification for what the new game is like.
Once you have this, since you will be rewriting the code, you may find that some of the business logic that doesn't deal with the console can be ported over. But, anything dealing with I/O, user interaction or graphics/sounds will be rewritten, so you might as well do that from scratch.
A specification is very important, to make certain that you know how the current game is working so that the new port will give the same user experience, if that is what is desired.
You may want to keep the same bugs, if that is part of the experience, as, if I know that in the Wii I can jump down and bounce off the wall to safely land, then if I can't do that in the new version then that may be bothersome.
Well porting a PS1 game to an iPhone would be quite a task they work in very different ways. I'm sure its doable but it will be a LOT of work to replace all the fixed point maths and lack of Z-Buffer based rendering to a real graphics chip.
Wii would be a lot easier. The Wii API is very similar to OpenGL. However the Wii has some very nice fixed function features that just are not available on any other GL based platform. Should be doable, though ...
I'm not really sure I can say anything more than that. Have signed far too many NDAs over the years to be 100% sure of what I can and cannot say ;)
Still if you want to hire someone to do some porting work and are prepared to supply the required hardware then I might be free ;)