Saturday, May 22, 2010

Joystick pong (how to write custom usb drivers for the nanoboard)

I've just worked out how to write custom drivers for the nanoboard to extend the capabilities of the platform through different USB devices. It isn't really that difficult for similar devices (you could just copy things across), but for more complicated devices you need to understand how the USB protocol works. The nanoboard USB host driver already takes care of a lot of the details for you. The specific device driver that you are writing only has to indicate if it wants to be a device driver for a particular detected device. The device driver call basically does a test using the data that is passed in. This data comes straight from the interface and device descriptors that were received from the bus. This is sometimes where the problems start. My joystick on Windows isn't recognized as a joystick per se. It's a Human Interface Device without a boot capability. It's working properly in games, but that's about it. The HID protocol isn't passed by it (which should be 04, for joysticks). This causes issues for people writing device drivers, because you can't know what type of device something is.

Also, not all joysticks pass the same ranges of data. The USB HID descriptor does indicate the ranges for USB, but this complicates things a bit for the device driver writer.

Anyway, the sample joystick driver is here and a new version of the pong game is here.
( the joystick driver should be put in the "Library/Software Platform/services/usbhost" directory of Altium designer).

In order to write drivers for other devices, it's helpful to boot into Linux and inspect the descriptors that are sent across the wire. A useful page comes from a guy who has rewired his old joystick to make it USB compatible. Other useful pages are the HID tools page and a page explaining how to use usbmon software to analyze the USB in more detail. Wireshark can also capture things from the USB. (usbmon on my lucid ubuntu seems to have been compiled into the kernel already. Just see if the /sys/kernel/debug/usb tree is there).

You can then use the kernel debug interface to inspect what's going on in the system. Under linux, cd'ing to:
will give you a devices file, which is useful to find out how a device is recognized. My joystick is incorrect, because it doesn't provide subclasses or protocols, as can be seen here:

T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=1.5 MxCh= 0
D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=046d ProdID=c215 Rev= 2.04
S: Manufacturer=Logitech
S: Product=Logitech Extreme 3D
C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr= 30mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=00 Prot=00 Driver=usbhid
E: Ad=81(I) Atr=03(Int.) MxPS= 7 Ivl=10ms

Compare that to the mouse (but notice how the same driver is used):
T:  Bus=07 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=1.5 MxCh= 0
D: Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=046d ProdID=c018 Rev=43.01
S: Manufacturer=Logitech
S: Product=USB Optical Mouse
C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=usbhid
E: Ad=81(I) Atr=03(Int.) MxPS= 5 Ivl=10ms
Another cool thing to do is to look under:
This will show a couple of weird ID's, but those are the currently attached devices. In those directories, you can inspect the rdesc file for each of them. The rdesc file describes the format of the data, so indicates to the host device driver how it should interpret the data stream.

Devices may have multiple interfaces. The keyboard and mouse typically have a 'boot' interface, which allows the devices to be configured in the boot sequence. Notice that under linux, the same 'usbhid' driver takes care of most HID devices. This is because of the rdesc file, indicating the way how the driver should interact with the device. I'm not exactly sure at the moment how the driver would communicate this to the applications or HAL layer above it in a generic way.

Notice that HID are not always strictly input devices. Some HID's have outputs (device input) which allow the setting of LED's, force feedback, etc.

So how does one read these HID files to discover the data format? Let's look at a simpler example, the mouse:
Logical Minimum(0)
Logical Maximum(1)
Report Size(1)
Report Count(3)
Report Offset(0)
Flags( Variable Absolute )
Logical Minimum(-127)
Logical Maximum(127)
Report Size(8)
Report Count(3)
Report Offset(8)
Flags( Variable Relative )
The logical minimum and maximum determine the value range. This could also be used to rescale the values if you want a consistent output. The "report Size" is the size in bits of one individual field. "Usage(x)" indicates the number of fields that are being described. Report Count(x) does the same. The Report offset(x) describes the offset of these fields within the entire data stream. So, this mouse protocol uses the three bits in the first byte to describe the state of up to three buttons. It uses 3 bytes after that, indicating X and Y motions and the motions of the wheel.

This is basically how I figured out how my joystick worked. You could also specify your own rdesc / hid file using the HID tools mentioned above. Of course, computers don't need to communicate in ASCII, they'd use the compiled HID information as an array of bytes to convey the same information. The manufacturer and product ID are 16-bit fields that need to be looked up in a file on the host somewhere, if one cares about it.

Update: Here's another version using a lower resolution and lower color palette. Because of the USB code and the other drivers, the generated ROM image is larger than 32k and doesn't fit in local processor memory. This requires the use of a small amount of RAM, which constantly reads in new code to execute whenever required from memory. This memory (SRAM) is the external RAM on the nanoboard, which is shared with the VGA driver. Because the VGA driver gets priority, the game slows down whenever the processor tries to update the frame (because the processor cannot read in code to execute from SRAM memory at the same time the frame is being drawn to the monitor).

Thursday, May 20, 2010


This is a late-night shot of the game Pong!, running on a soft-core TSK-3000 RISC processor on the nanoboard. You control the paddle with the remote left and right. There aren't that many examples on the Internet on how to use the actual VGA display for the nanoboards. Actually, I found none. There were two examples from the tutorials shipped with Altium designer that demonstrated how the VGA connector should be used. There are a number using the TFT display on the board, but that's too small for a couple of things.

Pong! on the nanoboard goes public domain. It's imperfect and inefficient, but it does show how to render things on the VGA monitor (not the TFT). This implementation uses double-buffering, which in embedded devices is very costly because of memory requirements.

The display is not yet stable, it's flickering due to issues with VSYNC. I haven't figured out yet how to use the interrupts properly and let the framework driver rely on them, or whether the API calls have been used correctly. I'm hoping for some feedback in the forums, after which I could provide some updates here and there and show better practices in doing this.

Another thing I'm looking into is the best practice for writing one's own drivers for USB. There's a software stack available that can already inspect USB signals and packets that tell a host device what a connected device is about. There's very likely going to be a point where someone wants to write their own USB device for interfacing with the nanoboard, but is wondering whether to start from scratch at the signal level, or whether the usb-host sw platform can be used in any way. Without hacking into the standard altium designer library that is.

Well, plenty of ground to cover still with this device. It's a lot of fun and I'm starting to find my way around it already. I'm feeling quite confident about my abilities to prototype using the hardware on and around the board. It's just so easy. The difficulties start to arise when more complicated designs are required, especially those requiring more memory or specific hardware protocols or interfaces (custom designs). As with the above, my next goal will be to find out how to connect a USB joystick (and I'll opensource that as well). And from there... onwards...

Wednesday, May 19, 2010

Tutorials finished!

Well, I got things up and running like a charm in the meantime. After the inital GB downloads (which may get fixed ? see comments previous post! ), I've completed most tutorials of the Nanoboard today. There were only three that I couldn't run due to some interoperability issue with the Xilinx tools, but that happens sometimes. It's been logged, noted and people are working on it!

So far... I can say it's truly amazing and a pleasure to work with this board, especially for those who are newbies in the field of electronics. The tutorials provide a very basic overview of what the board really can do, so keep that in mind. Of course those applications can be done quite easily on Arduino boards or whatever.

But then have a look at the extensive royalty-free library... you'll discover 119 subdirectories loaded with microprocessors, circuits, memory blocks, opamps and plenty of other electronics that can be inserted in the schematics diagrams. People at work sometimes do use some exotic hardware and this makes it likely I can find the same chips and IC's they work with. In combination with the other tools and outputs, you can generate all kinds of testbeds for running their code on this FPGA, but analyzing the signals or some other things to help out.

It wasn't very clear to me that the real use of the board is probably about trying out different processors and designs up-front, before you solder things together. But now that I think about it, this certainly makes sense. At work some people work on UAV's for example. They require very small, light-weight boards that provide lots of functionality and a good amount of processing power. Everything is embedded and hardware supported. You couldn't put a nanoboard in one of those planes due to weight and power cable concerns :). But simulating a particular board or processor, or just having a platform where you can run embedded ideas from is a great nice-to-have. Since it's very close to the PC that could run a simulator like FlightGear, you could just hook up this board to a FlightGear stream of simulation data, where the board must attempt to fly the plane level or other kinds autopilot functions.

So yes, I am certainly pleased with my purchase. If anybody is ever thinking of going into FPGA programming, this is the board you want. It's probably twice the price of a regular board, but you get three times the value back for it. The extensive library of 'soft-design' hardware, the ability to still run VHDL code on the chip, the way how it interfaces with your computer, the Altium Designer software (only for a year though, so check out the conditions) and the overall hardware that is attached to the board (TFT touch, PS/2, S/PDIF, USB, SD-card, MIDI, audio, RS-485, RS-232, ethernet, VGA-out).

Definitely recommended! It's Arduino++.

Monday, May 17, 2010

Altium Nanoboard 3000

I've managed to get my hands on a really cool FPGA board from Altium. It's very promising with a TFT touchscreen display, RS485, RS232, 3x USB 2.0, S/PDIF in-out, SD-card reader, headphones/line-in/line-out, 4-ch DAC, 4-ch ADC, 4x relays, PWM, SVGA output, MIDI and a TSK-3000A RISC 32-bit processor.

Unfortunately, where this technology is really amazing, getting things to work on your computer is not so. Your mind will dazzle from all the license files, registrations, threats about non-compliance with export restrictions and whatever else these companies come up with to make your life difficult. For someone having gotten used to Ubuntu and the software it brings through straight installs, getting a minimal "Hello World" out of this board is proving to be extremely challenging for a newbie. And I'm saying that as an experienced programmer.

The biggest crap factor are the Xilinx tools. They offer a "webpack", but the download is around 2.6GB (not much of a "webpack" if you ask me). The 12.1 version is incompatible with Altium Designer, so that's where problems are starting. So then I downloaded 11.1 as required, but that is not supported on Windows 7. Altium Designer so far has no particular problems with Windows 7. So I upgraded Altium Designer as much as possible, but that didn't improve the chances of compatibility with 12.1.

Basically, I got a dreaded "Xilinx ISE not found" message in red above my FPGA chip, which was actually due to a missing environment variable (no longer set in 12.1?). Altium Designer just picks up the "XILINX" path variable, which should point to the "ISE" subdirectory of the Xilinx ISE installation. If XILINX is not there, it will show the above message. Populating XILINX as the env variable by itself is not enough, as even a very simple example won't compile due to differences in compilation options.

If you get: "No Process Flow", then you should simple "configure" the project by right-clicking on the nanoboard icon in the devices view and generate the constraint files.

The information about what to do next is not really available on the Internet. Most suppliers lock down their forums entirely, so you need a login to find out if others have had the same problem. Since most companies probably follow the instructions on what OS to use and so on, this doesn't seem to have occurred much. Luckily, I found one solution that seems to be going to work. You need a lot of patience and flick your common sense in "off mode" for this to work:
  1. Download the ISE Webpack 11.1 anyway (2.6 GB or so).
  2. Download the ISE Webpack 11.3 as well (another 2.7 GB..... *sigh*). Downloading only 11.3 will not work, because the installer asks for the 11.1 install directory (hooray!). Even though the size of the installation file clearly shows otherwise.
  3. Then install 11.1, but not from the main folder. Go into "bin/nt" and start "xsetup.exe" from there.
  4. Wait for this to install. Takes a while. Feel free to *not* install "webtalk", because that just sends how you use the tools to xilinx and why'd you want to do that?
  5. Then install 11.3. It will ask for where you installed 11.1 to. 11.3 is luckily compatible with x64 already.
  6. This upgrade takes quite some time (apparently it checks every file if it needs upgrading?).
  7. Restart Altium Designer... and now it should show up. ( See "XILINX" environment variable if it doesn't ).
Another word on what these companies do that I find very strange. Altium Designer and Xilinx Webtalk basically monitor the way how you use the tools and send this over to their servers "for improving your experience". So you've got basically a hidden spy on your computer now that indicates to them what you use, how long you use it, on which days etc... ugh!

I'm certainly not some experienced FPGA designer, I just decided that I wanted to learn about this technology and play around with it. My intention is to grab a board that could do a number of interesting things, rather than starting from the bottom-level basics. Altium Designer allows me to focus on certain high-level topics, such that I can create some truly interesting marvels first before having to delve into the low-level details first. I prefer it that way, because I don't get hit by the low-level nit-picky details in the face immediately. Eventually however, I already noticed that one needs to gain the knowledge about electronics, wiring and so on in order to use these things effectively and knowledgeably.

My install got finished and it's all compiling now. I'm going to check through the tutorials, see if I can write a couple of things myself, play around with things a bit. Given the software that Altium provides, if you are a learner like me, I can certainly recommend what they are offering in these nanoboards...

Wednesday, May 12, 2010

Field Programmable Gate Arrays

I've been looking atFPGA's and ordered my own board to arrive in the mail pretty soon I hope. The difference between a normal CPU and an FPGA is best explained here. Notice how FPGA's are independent and act directly on the signal, whereas the CPU typically executes one instruction per 'clock cycle', but then may need to retrieve values from memory, put this into a register, execute another instruction, push back from register to memory and so on. Once you think about it, it's already pretty amazing that a single CPU can be so darn fast.

FPGA's however do not typically need to do this. It requires a totally different thinking about computing, but benefits from using much simpler logical elements wired together in different ways. This configuration of logic elements is what provides it with an application.

The FPGA's limitations are more the number of elements (and thereby the functionality it can possibly embed), because it's program is embedded in hardware and isn't read from memory and then executed by the same device. This is also how they are very different. FPGA's are also not programmed with a standard programming language (since it's inherently parallel and the program is basically the configuration how logic elements wire together). Another language called VHDL is used for this purpose, which does not require you to think about all things in parallel (one of the reasons why computers are easy to program is because we can think about events serially, as happening one-by-one. Multi-threaded computing is already getting more complicated, because you need to imagine how threads and processes may interact together and the results these may create).

You can build a host of very interesting things on FPGA's. One is an M&M sorter :), but a not too complex board can already simulate a C-64 and run the game Commando.

Of course, the FPGA gets very interesting when you need to process a large, complex signal. Think about video signals for video compression for example or speech recognition. Lots of research is undertaken there at the moment. But simpler implementations are also possible, for example PID controllers for temperature regulators etc... I do think though that FPGA's are slightly overkill and possibly unnecessarily complicated.

An alternative to FPGA's are Arduino boards, which are basically CPU's again and can also be programmed in C. So a lot of fun when you want a new kind of hobby.