Hi sylvia_intel,
Thanks for replying.
I completely understand what you are saying, and from my testing I fully agree with you. I have only 5 USB devices + 1 hub connected and I get the 'pop-up' message. I know that 4 of these USB devices each declare about 22 end-points, so 96 seems to be the limit I am hitting.
My post was really about understanding where the limit is - the Intel xHCI controller or the BIOS or the o/s?
Reading the Intel xHCI controller datasheet (Rev 1.1) it implies that it supports 255 device slots (end-points).
- Take a look at section 5.3.3 (page 287) - this specifies that MaxSlots can be in the range 1 to 255, where MaxSlots specifies the maximum number of Device Context Structures (end-points). This register is ReadOnly - so is it hard-coded by Intel and if so to what value??? Is this set to 96 ???
- Take a look at section 5.4.7 (page 308) - this specifies that MaxSlotsEn can be in the range 0 to MaxSlots. This is Read/Write, hence software can set it. Does the BIOS or the o/s set this???
- Take a look at section 6.2 (page 338 onwards) - this describes how the device contexts are stored in memory. Each device context can hold up to 32 entries (maximum defined by the USB spec). The device contexts must by held in memory - is this allocated by the BIOS or the o/s???
I still maintain that 96 is way to low considering that as part of the USB specification a USB device can declare up to 32 end-points. This means that theoretically the limit of 96 could be reached with only 3 USB devices connected !!!