Category: Electronics & Production

Getting started with GIT Revision Control

Revision Control is the most critical part of any project involving files. Otherwise you end up with tons of directories, and naming schemes like “report_final2_june.docx” along with 20 other copies.

This is best described in this 20-min clip. Sorry it’s a little long, but there is a fair amount to cover:


You can download the slide set:
Slide Set
For your reading pleasure, here are the highlights. I’ve linked to the exact moments of interest in the video rather than retype stuff I describe in the video.

What is GIT

Git is a revision control manager. Briefly, it lets you see how things changed and track those changes. Even better, it lets you do tasks like create a “branch” of the source code. You can switch back and forth between branches to deal with issues like wanting to rewrite sections of the code, while still being able to get back to the last good ‘release’ copy.
Show Me Branching

Getting stated on Your Computer

You can use GIT on any folder! It’s dead simple to do, and handy even if you will never commit things to the web. Doing so requires a few steps:

  1. Create a repository locally Show Me
  2. Commit initial fileShow Me
  3. Commit changes Show Me
  4. Do other stuff (branching, merging, etc) Show Me

Using Real Repositories

To use real remote repositories, you need a server to host them. I recommend assembla.com or bitbucket.org . bitbucket.org provides more storage, more users for free, and unlimited project sizes for university-based projects. Both are pretty cheap for commercial projects.

You want to configure a SSH key. Doing so requires four steps:

  1. Generate the key Show Me
  2. Set the key up on assembla/bitbucket Show Me
  3. Set the key up on git Show Me
  4. Set the key up to always be loaded Show Me

High-Speed ADC with Variable Gain Amp Input

Here is an ongoing project: it’s a high-speed ADC combined with some nice input preprocessing (amplifier). It’s all controlled by a FPGA on the Avnet LX9 Microboard, so it just plugs into that. Here is a simple python app (still being improved) to control it:
Image

Still need to measure analog BW to see how my layout stood out…

Avnet Spartan-6 LX9 Board: Or How ChipScope is your Saviour

I was recently working on a project which needed more gates than I had in my trusty current FPGA Board (Spartan3-200 on DLP-FPGA-HS). I quickly found the Avnet Spartan 6 LX9 board (AES-S6MB-LX9-G), which I could buy for $90 and have here in a few days. It also comes with a license for SDK for ChipScope, as it’s designed for experimenting with on-FPGA processors. It doesn’t have a full EDK license so you are a little limited in peripherals…

But for my project I didn’t care about that. I was however interested in ChipScope Pro, having used it previously at a job. This quick post will show you how valuable it can be – the license included with the LX9 board is “device locked” and will only work with XA6SLX9 parts. ChipScope Pro is not normally licensed as part of WebPack so the $90 board is a great deal when you consider the licensing cost.

My normal FPGA debugging, beyond Verilog testbenching, is to use a LogicPort on some spare IO lines. This works well – the LogicPort has a very high sampling rate (200MHz external, 500MHz internal). But it requires a physical connection, which requires a lot of IO pins. I was hoping ChipScope could eliminate this problem.

There is two cores of interest: the Integrated Logic Analyser (ILA) core, and the Virtual IO (VIO) core. They are both controlled by the Integrated Controller (ICON) core. You can only have one ICON, but it can control up to a number of ILA/VIO cores.

The VIO core gives you a virtual dashboard, where you can toggle bits and see results. This is pretty handy for validating/playing with cores to check they function as intended. Here I am checking a UART core from fpga4fun.com:


ChipScope Pro VIO

Note the VIO core doesn’t provide buffering, so data is transferred over the JTAG. This limits your polling speed of course, but makes it easy to play with things. It does let you define pulse trains or single pulses if you have special timing requirements on e.g.: load lines, as I had here.

The ILA core is strictly input. But it connects to BRAMs on-board the device, meaning you can buffer a fair amount of data. Since it’s all on-device the speed is basically limited by similar constraints to the rest of your design. Of course if you already have a packed chip you might not be able to spare any BRAMs…

Here I am debugging a state machine, note you how can even define ‘tokens’ so it decodes the states correctly:


ChipScope Pro ILA

 

So the combination of ChipScope ILA + VIO I’m hoping will make designs go by a lot faster.

LPCXpresso LPC1114 J4 JTAG Pinout

I recently got an LPCXpresso board, which you can cut and make into a debugger. I wanted to use the 0.1″ header (J4) and not the specified JTAG (2×10 0.5″) header. Here is how I cut my board such it can be plugged back together: the female header is just half an IC socket:

LPCXpresso Cut in half

Counting pin 1 at the top of the board (near J49), the pinout is:

1: +3.3V
2: TMS/SWDIO
3: TCLK/SWCLK
4: TDO/SWO
5: TDI
6: RESET
7: +5V
8: GND

RTCK is not present on this header, it’s only on J5. You may wish to consider not mounting pin 7 (+5V) since if you ever connect the plug wrong this will give you serious trouble, since +5V at high current is available. I ended up removing pin 7 and plugging it, so I also used that as a key on the other side of my connector. This prevents me from plugging in something backwards.
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Interfacing to 34401A

I recently got my 34401A bench meter out of storage, and wanted it working with my computer, something I hadn’t done for several years. I forgot to get my ‘official’ Agilent connection cable, but figured I could use my standard cables no problem.

This took a bit of effort to actually get working, so here is my notes on the issue:

  1. The required settings are 9600 Baud, 1 Start Bit, 2 Stop Bits, Hardware flow control. Hyperterminal never seemed to work, possibly because the 34401A uses full RTS/CTS + DTR/DSR flow control. I did however have success with the ‘Termite’ program with the following settings: Image
  2. Send the SYSTem:REMote command first, you should see a little ‘RMT’ appear on the 34401A VFD front panel. This indicates comms are working. Try a READ? command too; As an example see the following, blue is what I’ve sent and green is the meter responding: Image
  3. I first tried a small null-modem adapter + RS232 extension cable. You need to ensure your cable has all lines connected, since the 34401A uses full flow control. My null-modem adapter didn’t have lines 1 & 9 connected straight-through, as the 34401A manual says it should be. I figured it wouldn’t matter since it doesn’t claim to use them, and the rest of the lines were connected as required, but the meter didn’t respond to any commands. Using a null-modem cable which had line 9 connected straight-through, but not 1, seemed to work fine. So the hardware can be an issue!
  4. So far the Excel/Word Plug-In hasn’t worked for me. I know it did at one point, so still working on that, but I might end up just using Python or something instead anyway.

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Compass Circles

In my effort to build the calibration software for my simple Digital Compass, I’ve been working on doing tests with it.

Here is a screen-shot of the output (using MATLAB to interface to the serial port), it shows a plot of X & Y magnetic field readings plotted on X/Y axis. You can see it’s a (fairly) nice circle. The object will be mapping a distorted circle due to iron in the area onto something like that…

Image

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Making AT90USBKEY Run on 5V (Easy Way)

I needed to use my AT90USBKEY at higher than 3.3V for ADC input purposes. It’s not documented in the manual, but the schematic shows they anticipated this. You can easily convert the AT90USBKEY to run on 5V with a few changes. The changes needed are:

  • Remove resistor R20 (0-ohm resistor)
  • Remove resistor R16 (0-ohm resistor)
  • Place a 0-ohm resistor on pads at R21 (move R16 or R20)

That’s it! The DataFLASH chip’s VCC needs to be in the 2.5-3.6V range, but with those changes it is still powered by the 3.3V regulator. Thus you don’t need to remove the DataFLASH chips. The DataFLASH devices have 5V tolerant I/O, so even though your MCU is running at 5V, it won’t fry the DataFLASH. Note the logic high levels of the DataFLASH may not be sufficient to actually work with the MCU, since it’s logic high will only be using 3.3V logic.

The following diagram shows the changes, red = remove resistor, green = new resistor, yellow = optional change. I actually removed the DataFLASH in this photo only because I wanted the I/O lines the DataFLASH was using.
Image

Note that D3 drops the 5V input to about 4.2V. The actual VCC with just the resistor change is 4.2V. If you want full 5V from the USB, you also need to remove diode D3 and replace with a short. This is the change highlighted in yellow above.

When running from 5V you need to ensure the USB regulator is enabled. If using LUFA make sure the ‘USB_OPT_REG_ENABLED’ is enabled. e.g. in the Makefile:

LUFA_OPTS += -D USE_STATIC_OPTIONS="(USB_DEVICE_OPT_FULLSPEED | USB_OPT_REG_ENABLED | USB_OPT_AUTO_PLL)"

Another hint too: If you aren’t removing resistors permanently, just slide them onto one of the pads. This way you won’t lose the parts when you want to put them back. For example when I was using the line with the HWB pushbutton:

Image

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FIP – The Flexible IP(v6) Stack

I’m still working on finishing uploading & setting up documentation, but I’ve finally put some of a new IPv6 stack online.

It’s designed to fit in a variety of applications, including WSN where you might have anything from tiny 8-bit microcontrollers to full-blown ARM devices deployed. It’s currently not completely usable, but hopefully that will change soon with the upload of a complete example. As well some work by colleagues of mine will show it running as a more complete network, but that will be released as a separate project I think.

See the SourceForge project (with code) at http://sourceforge.net/projects/flexibleipfip/, and the Doxygen documentation at http://flexibleipfip.sourceforge.net/index.html
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