OHCI and/or UHCI and/or EHCI (for USB2) have to be included in the kernel. Check e.g. with lspci what your motherboard supports, it does not make sense to select both OHCI and UHCI, however they do not disturb each other.

To check what will be seen on the usb install usbutils for a command line tool or usbview for a gui tool. Make sure version >=2 gets emerged since for new kernels the devices file is no more under /proc/bus/usb/devices but now under /sys/kernel/debug/usb/devices. This file shows what appears on the bus. Alternative command line tools are:

lsusb

lsusb -t for tree view

you must emerge usbutils

e.g. Mount manually usb hard disc

mount -t vfat /dev/sda1 /mnt/usbhd

instead of -t vfat you can use auto.

mount -t auto /dev/sda1 /mnt/usbhd

Unmount it

umount /mnt/usbhd

Disable the low performance USB block driver (BLK_DEV_UB) since it conflicts with USB mass storage support that you have to select to be future oriented (USB_STORAGE). If you have a multi card reader select Probe all LUNs on each SCSI device (SCSI_MULTI_LUN) udev will create the sd* files in /dev if USB_STORAGE is selected. If BLK_DEV_UB is selected /dev/ub* would appear.

udevadm info -a -p $(udevadm info -q path -n /dev/sdc) is a useful command to see what is behind the device file.

According apacer you have to add an option to /etc/modules.conf. The clean way you create a file /etc/modules.d/apacer with the line from the manual

options scsi_mod max_scsi_luns=8

then run modules-update to put the line in /etc/modules.conf.

For USB2 check out if cables are USB compliant and are not too long e.g. Appearing and disappearing nodes on usbview and EHCI is in the kernel especially USBHD (you might have difficulties to mount them and they disappear and seem to loose data).

SUBSYSTEM=="usb", <matching argument> OPTIONS=="ignore_device"

USB supports 127 physical devices per host interface (the USB address has 7 bits). PC's can have multiple host interfaces.

cat /proc/bus/usb/devices or for newer kernels cat /sys/kernel/debug/usb/devices tells you what is attached.

T: Bus=01 Lev=01 Prnt=01 Port=05 Cnt=02 Dev#= 3 Spd=480 MxCh= 0

D: Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs= 1

P: Vendor=0dda ProdID=2026 Rev= 1.9c

S: Manufacturer=Generic

S: Product=USB2.0 Card Reader

S: SerialNumber=0000001

C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=500mA

I:* If#= 0 Alt= 0 #EPs= 2 Cls=08(stor.) Sub=06 Prot=50 Driver=usb-storage

E: Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms

E: Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms

This information is gathered via EP0 of each device, where different Standard Descriptors are read out:

This is the multi card reader is a USB2.0 device, having two endpoints #Eps=2 with bulk transfer, one endpoint for each direction. It is device number 3 on the first USB bus in the computer.

The Descriptors are requested using the following C structure.

typedef struct usbRequest{
  uchar       bmRequestType;
  uchar       bRequest;
  usbWord_t   wValue;
  usbWord_t   wIndex;
  usbWord_t   wLength;
}usbRequest_t;

The mentioned simple implementations, make use of marking the bmRequestType as vendor specific. After that a frame containing vendor specific data can be sent/received to/from the host.

The numbered directories in /proc/bus/usb represent one host interface but are not human readable.