Testing and Building with the New gumstix SBCs, Part 1
This time around, gumstix provided me with the gumstix connex board, which is one of the smallest FFMCs available. The board measures 3.15" x .8" x .25" (80mm x 20mm x 6.3mm) and can be powered by the USB connections. connex and basix both use the same Intel XScale PXA225 chip; the evaluated version was a 400MHz version rather than the 200MHz originally reviewed. There are several differences between the connex and basix, but the most obvious is the addition of a 92-pin header on the bottom of the connex and the loss of the MMC adapter, which the header essentially replaced. With the exception of the stated changes, the connex is basically identical to the basix.
Networking capability is a must for a truly full function computer. Originally gumstix provided networking only through Bluetooth. As capable as Bluetooth is, its performance and range simply is inadequate for a large number of interesting and important applications. Perhaps I am spoiled, but I consider 10/100BaseT support to be absolutely essential for a computer truly to be usable. I considered the lack of a high-speed networking capability to be a real handicap for the gumstix basix. gumstix rectified this handicap, though, by introducing the etherstix daughtercard.
The etherstix board connects to the gumstix connex board through the 92-pin bus header, and the board is built around the SMSC LAN91C111 chip, which is a dual-speed, full-duplex switched Ethernet chip. The board measurements excluding the RJ-45 connector are 3.75" x 1.1" x 0.23" (95mm x 28mm x 6.4mm), and including the RJ-45, the board measures 4" x 1.1" x 0.75" (101mm x 28mm x 19mm). The board is fairly simple in that it includes the RJ-45, the SMSC chip, the support chips, 92-pin bus connector and finally the power connector.
The etherstix functions as one would expect a network card to function. The principle difference between the etherstix/connex combination and a generic computer is the connex does not assume that the etherstix is installed. Out of the box, one must activate the drivers in order for the NIC to come up. This is done intentionally, in order to avoid accidental damage through inappropriate probing.
If there is one issue with the etherstix, it is the 92-pin connector. If the etherstix/connex is up and running and the 92-pin connector becomes dislodged, there is a fairly high probability that either or both of the modules will be damaged or destroyed. Lesson to be learned: don't mess with it when the unit is powered up.
Two different waysmall interface boards now are available, the waysmall STUART and the waysmall HWUART. waysmall HWUART was used exclusively with the original non-Bluetooth version of the basix module and thus is not discussed further here. The waysmall STUART board essentially converts the connex and basix-Bluetooth modules into waysmall computers, hence the name of the board. These boards, which measure 3.19" x 1.38" x 0.5" (81mm x 35mm x 12.7mm, provide access to the two serial ports, the USB port and the power supply, all through the Hirose 60-pin header.
During testing, this board worked as one would expect. Again, the only concern is the potential for disconnecting the two boards, but that is being address by the introduction of mounting holes in both the connex and waysmall STUART boards.
Overall, this board is quite useful and highly recommended. Even if you find that your final design does not allow it to be used, it can help you get to know the gumstix FFMC modules themselves. Personally, I have gone back to this board several times in order to diagnose problems.
One point that has come up since the original review is the ARM CPU handles overclocking quite nicely. We have it on good authority that the 200MHz chip reliably overclocks to 533MHz, which is a nice feature to have in your back pocket. As usual, temperature and longevity issues when overclocking an embedded, or any, processor. Overclocking the PXA255 is fairly simple. Within the uClibc directory under buildroot/build_arm lives include/configs/gumstix.h. This file contains a #define line that assigns a hex value that determines the CPU speed from 100MHz to 533MHz. We will look more closely at this potential in the next installment of this article
gumstix recommends the uClibc buildboot system, which is a Linux native toolchain. In the previous review we indicated that other toolchain options were available. Although there certainly are other options, gumstix has focused on uClibc, so we focus on it as well; however, we do so in the next installment.