Thank you for all the work that went into this.
I am testing USB 3 on a Thinkpad x230i for my headphone DAC, an ODAC-revB. I tested a Youtube video, and it does not begin playback. The relevant error is at the end of the pasted dmesg. I also tested this on a Thinkpad X1 Carbon Gen 4 to the same result, but that dmesg is omitted for brevity. I tried setting sndiod to use the DAC, as described in the FAQs (https://www.openbsd.org/faq/faq13.html#confaudio). This procedure is sufficient when I use a USB 2 port. --8<---------------cut here---------------start------------->8--- # rcctl set sndiod flags -f rsnd/1 # rcctl restart sndiod --8<---------------cut here---------------end--------------->8--- full dmesg: --8<---------------cut here---------------start------------->8--- OpenBSD 6.5-beta (GENERIC.MP) #798: Sat Mar 16 10:12:15 MDT 2019 dera...@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP real mem = 16872108032 (16090MB) avail mem = 16350453760 (15593MB) mpath0 at root scsibus0 at mpath0: 256 targets mainbus0 at root bios0 at mainbus0: SMBIOS rev. 2.7 @ 0xdae9d000 (69 entries) bios0: vendor LENOVO version "G2ET33WW (1.13 )" date 07/24/2012 bios0: LENOVO 2306CTO acpi0 at bios0: rev 2 acpi0: sleep states S0 S3 S4 S5 acpi0: tables DSDT FACP SLIC TCPA SSDT SSDT SSDT HPET APIC MCFG ECDT FPDT ASF! UEFI UEFI POAT SSDT SSDT UEFI acpi0: wakeup devices LID_(S4) SLPB(S3) IGBE(S4) EXP3(S4) XHCI(S3) EHC1(S3) EHC2(S3) HDEF(S4) acpitimer0 at acpi0: 3579545 Hz, 24 bits acpihpet0 at acpi0: 14318179 Hz acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat cpu0 at mainbus0: apid 0 (boot processor) cpu0: Intel(R) Core(TM) i3-3120M CPU @ 2.50GHz, 2494.75 MHz, 06-3a-09 cpu0: FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE,SSE3,PCLMUL,DTES64,MWAIT,DS-CPL,VMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,PCID,SSE4.1,SSE4.2,x2APIC,POPCNT,DEADLINE,XSAVE,AVX,F16C,NXE,RDTSCP,LONG,LAHF,PERF,ITSC,FSGSBASE,SMEP,ERMS,IBRS,IBPB,STIBP,L1DF,SSBD,SENSOR,ARAT,XSAVEOPT,MELTDOWN cpu0: 256KB 64b/line 8-way L2 cache cpu0: smt 0, core 0, package 0 mtrr: Pentium Pro MTRR support, 10 var ranges, 88 fixed ranges cpu0: apic clock running at 99MHz cpu0: mwait min=64, max=64, C-substates=0.2.1.1.2, IBE cpu1 at mainbus0: apid 2 (application processor) cpu1: Intel(R) Core(TM) i3-3120M CPU @ 2.50GHz, 2494.34 MHz, 06-3a-09 cpu1: FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE,SSE3,PCLMUL,DTES64,MWAIT,DS-CPL,VMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,PCID,SSE4.1,SSE4.2,x2APIC,POPCNT,DEADLINE,XSAVE,AVX,F16C,NXE,RDTSCP,LONG,LAHF,PERF,ITSC,FSGSBASE,SMEP,ERMS,IBRS,IBPB,STIBP,L1DF,SSBD,SENSOR,ARAT,XSAVEOPT,MELTDOWN cpu1: 256KB 64b/line 8-way L2 cache cpu1: smt 0, core 1, package 0 ioapic0 at mainbus0: apid 2 pa 0xfec00000, version 20, 24 pins acpimcfg0 at acpi0 acpimcfg0: addr 0xf8000000, bus 0-63 acpiec0 at acpi0 acpiprt0 at acpi0: bus 0 (PCI0) acpiprt1 at acpi0: bus -1 (PEG_) acpiprt2 at acpi0: bus 2 (EXP1) acpiprt3 at acpi0: bus 3 (EXP2) acpiprt4 at acpi0: bus -1 (EXP3) acpicpu0 at acpi0: C2(350@80 mwait.1@0x20), C1(1000@1 mwait.1), PSS acpicpu1 at acpi0: C2(350@80 mwait.1@0x20), C1(1000@1 mwait.1), PSS acpipwrres0 at acpi0: PUBS, resource for XHCI, EHC1, EHC2 acpitz0 at acpi0: critical temperature is 103 degC acpibtn0 at acpi0: LID_ acpibtn1 at acpi0: SLPB acpipci0 at acpi0 PCI0: 0x00000000 0x00000011 0x00000001 acpicmos0 at acpi0 tpm0 at acpi0: TPM_ addr 0xfed40000/0x5000: device 0x0000104a rev 0x4e acpibat0 at acpi0: BAT0 model "45N1023" serial 4025 type LION oem "SANYO" acpiac0 at acpi0: AC unit online acpithinkpad0 at acpi0 "PNP0C14" at acpi0 not configured "PNP0C14" at acpi0 not configured acpidock0 at acpi0: GDCK not docked (0) acpivideo0 at acpi0: VID_ acpivout at acpivideo0 not configured acpivideo1 at acpi0: VID_ cpu0: Enhanced SpeedStep 2494 MHz: speeds: 2500, 2400, 2300, 2200, 2100, 2000, 1900, 1800, 1700, 1600, 1500, 1400, 1300, 1200 MHz pci0 at mainbus0 bus 0 pchb0 at pci0 dev 0 function 0 "Intel Core 3G Host" rev 0x09 inteldrm0 at pci0 dev 2 function 0 "Intel HD Graphics 4000" rev 0x09 drm0 at inteldrm0 inteldrm0: msi inteldrm0: 1366x768, 32bpp wsdisplay0 at inteldrm0 mux 1: console (std, vt100 emulation) wsdisplay0: screen 1-5 added (std, vt100 emulation) xhci0 at pci0 dev 20 function 0 "Intel 7 Series xHCI" rev 0x04: msi, xHCI 1.0 usb0 at xhci0: USB revision 3.0 uhub0 at usb0 configuration 1 interface 0 "Intel xHCI root hub" rev 3.00/1.00 addr 1 "Intel 7 Series MEI" rev 0x04 at pci0 dev 22 function 0 not configured em0 at pci0 dev 25 function 0 "Intel 82579LM" rev 0x04: msi, address 3c:97:0e:36:95:a5 ehci0 at pci0 dev 26 function 0 "Intel 7 Series USB" rev 0x04: apic 2 int 16 usb1 at ehci0: USB revision 2.0 uhub1 at usb1 configuration 1 interface 0 "Intel EHCI root hub" rev 2.00/1.00 addr 1 azalia0 at pci0 dev 27 function 0 "Intel 7 Series HD Audio" rev 0x04: msi azalia0: codecs: Realtek ALC269, Intel/0x2806, using Realtek ALC269 audio0 at azalia0 ppb0 at pci0 dev 28 function 0 "Intel 7 Series PCIE" rev 0xc4: msi pci1 at ppb0 bus 2 sdhc0 at pci1 dev 0 function 0 "Ricoh 5U822 SD/MMC" rev 0x07: apic 2 int 16 sdhc0: SDHC 3.0, 50 MHz base clock sdmmc0 at sdhc0: 4-bit, sd high-speed, mmc high-speed, dma ppb1 at pci0 dev 28 function 1 "Intel 7 Series PCIE" rev 0xc4: msi pci2 at ppb1 bus 3 iwn0 at pci2 dev 0 function 0 "Intel Centrino Advanced-N 6205" rev 0x34: msi, MIMO 2T2R, MoW, address 60:67:20:42:68:52 ehci1 at pci0 dev 29 function 0 "Intel 7 Series USB" rev 0x04: apic 2 int 23 usb2 at ehci1: USB revision 2.0 uhub2 at usb2 configuration 1 interface 0 "Intel EHCI root hub" rev 2.00/1.00 addr 1 pcib0 at pci0 dev 31 function 0 "Intel QM77 LPC" rev 0x04 ahci0 at pci0 dev 31 function 2 "Intel 7 Series AHCI" rev 0x04: msi, AHCI 1.3 ahci0: port 0: 6.0Gb/s scsibus1 at ahci0: 32 targets sd0 at scsibus1 targ 0 lun 0: <ATA, KINGSTON SV300S3, 505A> SCSI3 0/direct fixed naa.50026b723902475d sd0: 114473MB, 512 bytes/sector, 234441648 sectors, thin ichiic0 at pci0 dev 31 function 3 "Intel 7 Series SMBus" rev 0x04: apic 2 int 18 iic0 at ichiic0 spdmem0 at iic0 addr 0x50: 8GB DDR3 SDRAM PC3-12800 SO-DIMM spdmem1 at iic0 addr 0x51: 8GB DDR3 SDRAM PC3-12800 SO-DIMM isa0 at pcib0 isadma0 at isa0 pckbc0 at isa0 port 0x60/5 irq 1 irq 12 pckbd0 at pckbc0 (kbd slot) wskbd0 at pckbd0: console keyboard, using wsdisplay0 pms0 at pckbc0 (aux slot) wsmouse0 at pms0 mux 0 pcppi0 at isa0 port 0x61 spkr0 at pcppi0 vmm0 at mainbus0: VMX/EPT error: [drm:pid0:cpt_set_fifo_underrun_reporting] *ERROR* uncleared pch fifo underrun on pch transcoder A error: [drm:pid0:intel_pch_fifo_underrun_irq_handler] *ERROR* PCH transcoder A FIFO underrun uhidev0 at uhub0 port 1 configuration 1 interface 0 "Yoyodyne Consulting ODAC-revB" rev 1.10/0.01 addr 2 uhidev0: iclass 3/0 uhid0 at uhidev0: input=19, output=28, feature=0 uaudio0 at uhub0 port 1 configuration 1 interface 3 "Yoyodyne Consulting ODAC-revB" rev 1.10/0.01 addr 2 uaudio0: class v1, full-speed, sync, channels: 2 play, 0 rec, 3 ctls audio1 at uaudio0 uhub3 at uhub1 port 1 configuration 1 interface 0 "Intel Rate Matching Hub" rev 2.00/0.00 addr 2 uvideo0 at uhub3 port 6 configuration 1 interface 0 "Chicony Electronics Co., Ltd. Integrated Camera" rev 2.00/5.18 addr 3 video0 at uvideo0 uhub4 at uhub2 port 1 configuration 1 interface 0 "Intel Rate Matching Hub" rev 2.00/0.00 addr 2 vscsi0 at root scsibus2 at vscsi0: 256 targets softraid0 at root scsibus3 at softraid0: 256 targets sd1 at scsibus3 targ 1 lun 0: <OPENBSD, SR CRYPTO, 006> SCSI2 0/direct fixed sd1: 114470MB, 512 bytes/sector, 234435953 sectors root on sd1a (cf7f15501dc7b7fb.a) swap on sd1b dump on sd1b uaudio0: can't get iface handle uaudio0: can't get iface handle audio1: failed to start playback uaudio0: can't get iface handle --8<---------------cut here---------------end--------------->8---