4 ms·
If I’m reading it right, don’t you give up USB to get this PCIe access?
by girvo 7y ago
If I’m reading it right, don’t you give up USB to get this PCIe access?
- megous 7y agoYes, that's my point.
- londons_explore 7y agoBet the broadcom SoC has a USB controller built in, but unused... You could hook it up?
- megous 7y agohttps://lb.raspberrypi.org/documentation/hardware/raspberrypi/usb/README.md https://lb.raspberrypi.org/documentation/hardware/raspberryp... This says, there's OTG controller intended to be used in "peripheral device only" mode. I haven't found datasheet for BCM2711, so it's hard to tell.
- londons_explore 7y ago> peripheral device only mode. I wonder why? The silicon required is far far simpler for host mode (since you only need a single memory buffer, and you fully dictate the timing, so can pass all the complex stuff up to software).
- megous 7y agoMaybe they don't have the VBUS circuitry setup for connecting self-powered devices in host mode.
- monocasa 7y agoThere's an XHCI controller in the device tree, but my guess is that there's some silicon bug in it, hence the third party chip off of PCIe instead.
- megous 7y agoAlso it's probably not routed from the BGA, so it would not be possible to use anyway.
- cesarb 7y agoIs it really unused? The RPi4 schematic is incomplete, but it at least shows the USB 2.0 pins of the USB-C port going somewhere; they might be going directly to that built-in USB controller in the main SoC.