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Re: serial port signal path

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Computer Nerd Kev <not@telling.you.invalid> wrote:
> bp@www.zefox.net wrote:
>> Does anybody happen to know how data travels between gpio pins
>> 8 and 10 and the system console? In other words, what hardware
>> and maybe software facilitate the exchange? For example, the
>> internal ethernet adapter is connected to the CPU via USB. Is
>> something analogous for the system console?
> 
> I know with the BCM2835 (Pi 1 and Zero) both the UARTs (serial
> ports) are part of the SoC, as described in the peripherals
> documentation (often called the datasheet, though it's not really).
> They're "peripherals", but part of the chip so the signals connect
> directly - definitely no USB interface in-between. Other RPis
> _could_ be different but it's extremely unlikely because at least
> one UART peripheral is pretty essential, even just during product
> development.
> 
Ok, that largely answers my question. If the console is stand-alone
the mischief isn't related to some intermediate driver software.

>> I'm seeing what look like console failures on older-model Pi2s
>> (v1.1) and wondering if some accessory subsystem, (usb comes
>> to mind but I don't think that's it specifically) when running
>> FreeBSD-current.
> 
> Even though it's part of the same SoC as the CPU and other things,
> the UART is still something that can fail or be misconfigured even
> if there's nothing like USB in-between. Running a program/script
> that toggles the power light on/off (or another GPIO signal that
> you monitor) would indicate whether the CPU is still running when
> the serial console hangs.
> 
>> The machine stops without complaint or warning, does not answer
>> ping and has to be power cycled.
> 
> Since it doesn't respond to a ping either, that suggests that it's
> probably crashed completely.

That's my present supposition also. 

Thanks for writing!

bob prohaska

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serial port signal path bp@www.zefox.net - 2026-01-28 22:06 +0000
  Re: serial port signal path not@telling.you.invalid (Computer Nerd Kev) - 2026-01-29 09:12 +1000
    Re: serial port signal path bp@www.zefox.net - 2026-01-29 00:31 +0000

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