Hi Neil
I don't understand about the serial transmission because USB doesn't have setting like a serial interface. Its speed is fixed (eg. 12Mb/s for full speed) although its bandwidth can be controlled to achieve certain throughput limits. It has no stop bit but data is sent in packets (tokens). I would get them to explain in more details what is meant.
It may be that they are talking about the PC side, where the USB peripheral can be 'seen' as a COM port with serial settings (?) but this would probably use CDC (Communication Device Class).
OTG has some different rules (different connectors/cables) and both ends of the connection should be OTG capable otherwise the OTG protocol can not be used - if the other side is purely a device then HOST is the mode to use and not OTG.
I am hoping to start on the host mode very soon but it is difficult to estimate how long it will take since the main goal is to support mass storage, although CDC host is probably the logical first step seeing ans CDC device exists - this would also help testing OTG since CDC class seems suitable for this.
USB uses differential signaling which is not very suitable for a logic analyser. Also it is difficult to interpret the data since it is based on a 1ms frame. I use an Ellisys USB explorer (cost about $3'500) but can also do high speed USB. There are cheaper and also much more expensive ones;
also a SW USB sniffer will allow the data traffic to be monitored but not low level things such as enumeration (where I found the main difficulty to lie). I have found that I don't use it much (apart from when actually developing embedded USB drivers) but I am glad that I have it when it is needed. I don't know whether such an investment is suitable for all USB users though -
in some projects I have received HW for a short time to measure and then all details could be solved with help of the Ellisys.
Regards
Mark
See some (USB device) development details here:
http://www.utasker.com/forum/index.php?topic=176.0