This repository contains the source code to a small C-language program that can be compiled + executed on a Linux system running the AMD APU SoC such as those used in the APU2/3/4 boards of PC-Engines.
The tool will re-configure the USB ports of the APU SoC to route USB Ports 8+9 (those exposed on the physical USB-A connectors of the PC-Engines boards) from XHCI to EHCI.
Why would one want to do this? To work around bugs in the XHCI controller firmware, such as miscalculation of the available isochronous bandwidth for full-speed devices. For OHCI/UHCI/EHCI, the operating system (Linux kernel) is responsible for this, and it does tend to get it right. With XHCI, this is implemented in proprietary vendor firmware, which does tend to get it wrong.
The official homepage / repository of the project is https://git.sysmocom.de/sysmocom/apu-ehci
You can clone from the official libosmocore.git repository using
git clone https:///git.sysmocom.de/apu-ehci
As long as you have a C compiler and make installed, all you need to do
is to run make to build this.
The following command will enable the USB-to-EHCI routing:
./apu-ehci enable
Which should render something like this in your dmesg:
usb 2-1: USB disconnect, device number 2
pci 0000:00:16.0: [1022:7808] type 00 class 0x0c0320
pci 0000:00:16.0: reg 0x10: [mem 0x00000000-0x000000ff]
pci 0000:00:16.0: supports D1 D2
pci 0000:00:16.0: PME# supported from D0 D1 D2 D3hot D3cold
pci 0000:00:16.0: BAR 0: assigned [mem 0xe0000000-0xe00000ff]
pci 0000:00:16.0: enabling device (0000 -> 0002)
pci 0000:00:16.0: PME# does not work under D3, disabling it
ehci-pci 0000:00:16.0: EHCI Host Controller
ehci-pci 0000:00:16.0: new USB bus registered, assigned bus number 4
ehci-pci 0000:00:16.0: applying AMD SB700/SB800/Hudson-2/3 EHCI dummy qh workaround
ehci-pci 0000:00:16.0: debug port 2
ehci-pci 0000:00:16.0: irq 55, io mem 0xe0000000
ehci-pci 0000:00:16.0: USB 2.0 started, EHCI 1.00
usb usb4: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 5.10
usb usb4: New USB device strings: Mfr=3, Product=2, SerialNumber=1
usb usb4: Product: EHCI Host Controller
usb usb4: Manufacturer: Linux 5.10.0-10-amd64 ehci_hcd
usb usb4: SerialNumber: 0000:00:16.0
hub 4-0:1.0: USB hub found
hub 4-0:1.0: 2 ports detected
usb 4-1: new high-speed USB device number 2 using ehci-pci
usb 4-1: New USB device found, idVendor=0438, idProduct=7900, bcdDevice= 0.18
usb 4-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
hub 4-1:1.0: USB hub found
hub 4-1:1.0: 2 ports detected
Furthermore, the USB device[s] attahced to port 8/9 should now re-enumerate on the new bus:
usb 4-1.1: new full-speed USB device number 3 using ehci-pci
usb 4-1.1: New USB device found, idVendor=1d50, idProduct=6145, bcdDevice= 0.03
usb 4-1.1: New USB device strings: Mfr=2, Product=3, SerialNumber=1
usb 4-1.1: Product: icE1usb
usb 4-1.1: Manufacturer: osmocom
usb 4-1.1: SerialNumber: dc697407e7881531
You can theoretically disable it again with the following command (not working here):
./apu-ehci disable
WARNING:: The tool meddles with low-level internals of the APU SoC, so
there is a risk it may crash, lock up or otherwise behave strangely. If
you want to be safe, it is recommended to first unload the ehci_pci
and xhci_pci modules before calling the apu-ehci tool. YMMV.
Official AMD BIOS and Kernel Developer Guide available from https://www.amd.com/system/files/TechDocs/52740_16h_Models_30h-3Fh_BKDG.pdf