D-meter updates

I’ve been able to do some more work on the divergence meter now. The university’s labs made short work of the surface-mount soldering, but there were some hitches in the assembly and testing phase, in which I discovered some of the part footprints were wrong, and it was a bit of trouble getting the programmer working.

I was able to work around most of the bad footprints, but some of them were barely salvageable, since the through-holes were too small. I was able to drill them out on the drill press in the lab, but that left me with very small contact areas to solder to, so I had a few hideous solder joints.

After getting the power supply portions of the board soldered came getting the MSP430 talking to my MSP430 Launchpad, which I’m using as a programmer. Initial attempts to program the micro were met with silence (and mspdebug reporting no response from the target), but the problem turned out to be due to using cables that were too long- I had simply clipped test leads onto the relevant headers, yielding a programming cable that was around 1 meter long, while the MSP430 Hardware Tools User’s Guide (SLAU278) indicates that a programming cable should not exceed 20 cm in length. I assembled a shorter cable in response (by soldering a few wires onto the leads of a female 0.1″ socket) and all was well.

The most recent snag in assembly was the discovery that I had botched some of the MSP430’s outputs. I had connected the boost converter’s PWM input to Timer A output 0 on the micro, but I discovered while writing the code to control the boost converter that it’s impossible to output PWM on output module 0, due to the assignment of SFRs for timer control. The user’s manual for the chip even mentions this, but I simply failed to appreciate it.

I could have cut the a few traces and performed a blue wire fix, but it seemed like a very poor solution, and I was still concerned about the poor contact on the other vias I had to drill out, so I bit the bullet and created a new revision of the board with correct footprints for all the parts, and a more comprehensive ground plane (hopefully reducing inductive spiking on the optocoupler control lines). I’ve now sent revision 1.1 out to be made, so improved boards will be here in a few weeks. Until then, I’ll be working on the software a bit more, and hopefully updating this post with photographs.

Static libpng on win32 with CMake

Working on mkg3a upgrades for libpng more, I was getting unusual crashes with the gnuwin32 libpng binaries (access violations when calling png_read_int()).  It turned out that the libpng dll was built against an incompatible C runtime, so I had to build static libraries.  With the official libpng source distribution (and zlib), building static libraries was reasonably easy.  Using the MSVC make tool in the libpng source tree, I first had to build zlib. The default build (for some reason) doesn’t build the module containing _inflate_fast, so I had to add inffast.obj to the OBJS in zlib/win32/Makefile.msc (this manifested as an unexported symbol error when linking a program against zlib). Building it then was easy, using nmake in the Visual Studio toolkit:

zlib-1.2.5> nmake -f win32/Makefile.msc

With zlib built, copy zlib.h and zlib.lib out of the source directory and into wherever it will be used.

For libpng, we first have to modify the makefile, since the one included uses unusual options. Change CFLAGS to read CFLAGS=/nologo /MT /W3 -I..zlib for some sane options. The include path also needs to be updated to point to your zlib.h. In my case, that makes it -I..include. The rest of the procedure for building libpng is very similar to that for zlib:

lpng158> nmake -f scripts/Makefile.msc

Building against libpng then requires png.h, pngconf.h, pnglibconf.h and png.lib. To build against these libraries, I simply put the include files in an ‘include’ directory, the .lib files in a ‘lib’ directory, and pointed cmake at it.

Warnings about runtime libraries when linking a program against these static libraries is an indication that you’ll probably see random crashes, since it means theses static libraries are using a different version of the runtime libraries than the rest of your program. I was this problem manifested as random heap corruption. Changing CFLAGS (in the makefiles) to match your target configuration as set in Visual Studio and rebuilding these libraries will handle that problem.