On Fri, Oct 15, 2021 at 2:09 PM Marc SCHAEFER <schae...@alphanet.ch> wrote:
> Hello, > > I made the following setup work, that is I can send break and '?' > (to get the magic sysrq help) or 's' to do an Emergency sync, and the > kernel logs it: > > laptop apu2 > USB serial port ------- null modem ------- ttyS0 internal 16550A > > (an apu2 is an embedded amd64 computer [4]) > It's a side issue, not my main question, but.... If feel some details are missing in the "apu2 null modem" block-box there :-) > As it works, of course MAGIC_SYSRQ is enabled, including for serial > ports, and the correct value is in the /proc pseudo-file. > > It works with the getty enabled or disabled. > > However, the following does not work to support magic sysrq, although > bidirectionnal communication also works with cu [5], with the correct > speed set: > > laptop apu2 > USB serial port ------- null modem ------- USB serial port > But don't you need to have a running getty now? Listening on the serial device file that should be associated with the USB source. Interesting project though. Any involvement here with MIDI-over-USB? Tschuss.... First, reading documentation, I thought that this would not be possible > [1], but then, reading kernel source, it looks it should work with my > adapter: > > Oct 11 14:30:56 apu2-init7 kernel: [ 9.915105] usb 2-2: pl2303 > converter now attached to ttyUSB0 > > since the driver [2] contains code for magic sysrq, see line 993 for > sysrq mode and line 892 for break handling, with implementation in [3] > (lines 589-597). > > I am running Debian buster kernel 4.19.0-18-amd64 on the apu2. > > Should I abandon all hope to make it work with USB, or should it work? > > Thank your for any pointers. > > [1] https://www.kernel.org/doc/Documentation/admin-guide/sysrq.rst > "On the serial console (PC style standard serial ports only)" > > [2] > https://github.com/jplozi/linux-4.19/blob/loadbalancing/drivers/usb/serial/pl2303.c > > [3] > https://github.com/jplozi/linux-4.19/blob/loadbalancing/drivers/usb/serial/generic.c > > [4] https://pcengines.ch/apu2.htm > > [5] https://linux.die.net/man/1/cu > from the days before 2003 where I was doing UUCP > cu -l ttyUSB0 -s 9600 > >
