Within the airprobe.org community, Piotr has recently a new GSM receiver codebase that he has developed. It seems like the reception/decoding quality is significantly better than gsm-tvoid, at least from my experience. But it might just be me using gsm-tvoid in a suboptimal way.
Today, Piotr has managed to fix some of the bugs regarding certain BSIC configurations, and I can also decode Um traces that were captured from a nanoBTS running with OpenBSC.
Piotr also has already integrated my old gsmtap code that I was hacking on during FOSS.in/2008. As I've also received in e-mail today: The pcap data link type for the GSMTAP header has been assigned.
I'm spending a bit more time testing the entire stack, but I'm confident the GSMTAP wireshark dissector can be submitted soon - closing yet another gap for GSM protocol analysis.
However, there still remains a lot of work to do for airprobe.org. I am willing to put in some time to help the gsm-receiver along, particularly for the layer2/layer3 decoding, which will then feed the channel configuration and CCCH configuration back into the upper half of layer 1 that takes care of generating MAC blocks from the actual GSM bursts.