hint.uart.1 in device.hints causes freeze at boot

[Marcel Moolenaar]

> On Feb 27, 2016, at 5:54 AM, Lundberg, Johannes <johannes at brilliantservice.co.jp> wrote:
> 
> >though I've no clue why or how that should cause a boot failure?
> 
> Verbose logging don't give any clues either.. It just stops.

On the Atom SoC I have, you can configure the UARTs as PCI or ACPI devices.
They work as PCI devices but required better support for memory mapped low-
level consoles in x86. If configured as ACPI (supposedly compatible), they just
don’t work. I belief FreeBSD would just hang when configured as ACPI, but I’m
foggy on that detail.

Key is that they we’re trimmed-down UARTs (3-wire functionality) and thus weird
beasts...

Johannes: If your BIOS has the same capability, try switching. PCI mode is well
supported in FreeBSD, though requires something like the following in your
loader.conf:

hw.uart.console="mm:0xd0810000,br:115200,rs:2,xo:44236800

This tells the uart(4) driver that the device is memory mapped (at I/O
address 0xd0810000, uses 32-bit register access and has a non-standard
clock input of 44236800 (=44Mhz).

--
Marcel Moolenaar
marcel at xcllnt.net <mailto:marcel at xcllnt.net>

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