The new USB Drivers included in Linux 2.4.13 and up do support the "OHCI" usb controller in the Compaq Evo N400c. See below.
I have also included some more Linux/USB information at the end.
I bought the Compaq External USB floppy drive (PN 230942-B21) at a Compaq dealer for 70.32 euros.
The new Linux USB stack first included in 2.4.13 supports the OHCI controller in the Evo N400c perfectly.
I have to do nothing on the kernel side. The kernel shipped with Col 3.1.1 had already compiled USB module. Only thing to do was activate the module the same way as I did with Sound or APM (see corresponding sections).
The floppy drive belongs to the "USB Mass Storage" category devices on USB. The driver is really an interface
between the USB stack and the SCSI layer. The mass storage driver presents the USB device as a SCSI device.
If you are compiling a new kernel you would need "SCSI support". You should also turn on subordinate options as
appropriate to your mass storage device: SCSI disk support. You do not need to do this if you use the Col 3.1.1
default kernel which brings all these like modules.
After inserting the floppy drive, you should check the /proc/scsi/scsi. Information about your device should be listed.
You can now mount your device. The best way is to make suitable entries in /etc/fstab. I inserted the followin line:
/dev/sda /mnt/usbfd auto noauto,user 0 0
Whenever I know I am going to need the USB floppy drive I used to boot the system with the unit already inserted. In any case the
floppy drive can be hot plugged without problem. The USB module involved is "usb-uhci".
If you're interested in how USB works in general, start here, then read this, this, and this.