Hi Forest,
On 10.01.2024 15:18, Forest Crossman wrote:
On Tue, Jan 9, 2024 at 4:52 AM John Crispin <j...@phrozen.org> wrote:
---SNIP---
* Why is there no USB 3.x host port on the device?
- the USB 3.x and PCIe buses are shared in the selected SoC silicon,
hence only a single High-Speed USB port is available
Perhaps you've already considered this, but it may be possible to
route the shared PCIe/USB 3 traces to both an M.2 slot and a USB 3
host port using a high-speed dual-channel differential 1:2/2:1
switch/mux. It wouldn't enable both interfaces to be used at the same
time, but it would make it possible to select which interface is
enabled using a GPIO pin. Then U-boot could either automatically
enable one port or the other depending on what devices it detects
(e.g., enable PCIe and disable USB 3 if a PCIe device is connected,
otherwise enable USB 3 and disable PCIe), or it could be statically
configurable via a U-boot environment variable.
I suppose this should work (I couldn't find anything which would prevent
using pure h/w analog mux on the bus with a runtime configuration) but I
don't think there is a way to actually test it without a custom hardware
(usually anything which doesn't exist in reference design/s from the
chipset vendor must be tested in target configuration). Assuming bus
speeds we are talking here about, I'm not sure this can be tested with
some home-based tinkering ;)
I'm afraid that might delay the project but I will ask around.
From some quick searching, the switches/muxes that would enable this
cost less than $1 each in qty. 1000. For a <$100 product I understand that
may be too much of an increase to the BoM cost and PCB complexity, but
I think users would really appreciate being able to choose between
being able to add an M.2 SSD, WiFi card, or SATA controller and being
able to plug in a USB 3.x 2.5 GbE adapter, SSD/flash drive, WiFi
dongle, or 5G modem.
This would also require a bit more current capacity in the USB Type-A
connector if we decide to make it 3.x.
--
Cheers,
Piotr
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