Day of success
Today I got Linux - and audio! - working on the Beagle Board. And my HL-340 USB-to-serial adaptor under Linux.
Today was a good day; I got Linux running on the Beagle Board, including audio in- and output.
The Beagle Board ships only with a bootloader; there is no actual operating system pre-installed. Yesterday in the evening, after a quick verification of the bootloader working, I tried to install Linux and boot from SD card, but that failed. I think the reason was that I used the standard Windows Explorer formatting tool for formatting the SD card, since the HP formatting tool suggested in the Beagle Board's hardware reference manual did not seem to work for me. I suspect that the Windows formatting tool puts some stuff at the position of the first cylinder, where the MLO file needs to be in order for the boot from SD card to work.
This morning, I then took a different approach and formatted the SD card under Linux, using the fdisk tool. This seems to have done the trick. I ended up with a booting kernel, a full-grown Linux file hierarchy, and a working shell on the Beagle Board. All of this I did by accessing the Beagle Board through its serial port, using the TeraTerm terminal program under Windows as a host. Later I figured out how to make my HL-340 USB-to-serial adaptor work under Linux, so now I use the minicom terminal program under Linux as a host for accessing the board.
And I did some of the tests suggested in the Beagle Board hardware reference manual: I figured out how to use it as a USB client to a Windows host machine, and I also tried to use it as a USB host, in order to connect a keyboard an mouse to it. The mouse worked, but the keyboard didn't. I assume this might have to do with the keyboard itself including two USB ports for attaching mice, etc.
But most importantly, I succeeded in recording and playing back audio using arecord and aplay! The sound quality does not seem to be too bad, which is a relief.