>> >> Is there any way to set the latency timer for a USB device? >> > >> > In general, USB devices don't have latency timers. What are you >> > referring to? >> > >> > Alan Stern >> >> In light of that, I must be looking for a way to set the latency timer >> for a USB bus. Some dmesg output: >> >> ehci_hcd 0000:00:02.1: setting latency timer to 64 >> ehci_hcd 0000:00:04.1: setting latency timer to 64 >> ohci_hcd 0000:00:02.0: setting latency timer to 64 >> ohci_hcd 0000:00:04.0: setting latency timer to 64 >> >> I'd like to experiment with some different values for fun. > > ehci-hcd has a module parameter named log2_irq_thresh. Is that > what you're interested in? It is the Interrupt Threshold Control value > in the EHCI USBCMD register. What function does the USB Interrupt Threshold Control value have? I'm actually more interested in tuning OHCI than EHCI. It looks like log2_irq_thresh can be applied to usbcore as well as ehci-hcd, but I can't find mention of it related to ohci-hcd. Do you know what the valid range of values are? Is there any way to read the value? > It doesn't corresponds to those dmesg lines, however -- they come from > pcibios_set_master() in arch/x86/pci/i386.c, which is concerned with > bus mastering rather than interrupts. And they refer to a PCI control, > not a USB control. OK, I think setpci can be used to set PCI device latency timers. Do you know of any other USB tuning parameters that could affect latency or timing, even if only on a very small or theoretical scale? - Grant -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
