In some hardware designs, multiple UARTS may be available behind a Mux, which requires obmc-console to select one at a time.
For example, let's say behind /dev/ttyS0 there are UART1 and UART2, behind a mux. GPIO UART-MUX-CTL can be used to select one. This scenario is shown in the Example Diagram
Then there will be one obmc-console-server process, and 2 consoles will be created in this server process.
The obmc-console-server will receive configuration for both consoles detailing the gpios to be used to control the mux and the values they should have when they are active.
The implementation documented here has been made based on the design document
The kernel will not be aware of this mux and the support can be implemented in userspace.
Reasons for this are that the hardware this is for is not static (blade server) and thus cannot be represented by devicetree. Also, it is unclear how the virtual uart should notify a process that the mux state has changed.
When a userspace implementation is available for reference, this may later pave the way for a kernel implementation if someone wants to do that.
The configuration is similar to i2c-mux-gpio in the linux kernel.
The order of GPIOs listed in 'mux-gpios' forms the LSB-first bit representation of an N-bit number that is taken from 'mux-index'.
For declaring the different consoles, the section name, e.g. [host1] must be the same as the console-id. All of the section names need to be unique.
$ cat server.conf mux-gpios = MUX_CTL [host1] mux-index = 0 logfile = /var/log/console-host1.log [host2] mux-index = 1 logfile = /var/log/console-host2.log
Now the server can be started. See the Dbus Interface and Example Diagram
$ obmc-console-server --config server.conf /dev/ttyS0
Mux Control happens implicitly via connections. When a client connects to a console, the new connection is accepted and the console-server switches the mux to this console. Any clients connected to other consoles are disconnected.
$ obmc-console-client -i host2 & [1] 3422 $ obmc-console-client -i host1
Connecting to console 'host1' will cause console 'host2' to:
Then the following happens for console 'host1':
Whenever the mux is switched, there should be a way for people reading the log to know that that console was (dis)connected, and at which time. Otherwise there may be confusion as to why there is a gap in the logs.
So obmc-console-server will print one of these messages to all clients:
[obmc-console] %Y-%m-%d %H:%M:%S UTC CONNECTED
[obmc-console] %Y-%m-%d %H:%M:%S UTC DISCONNECTED
Note that this log message is not a reliable source of information, and is only provided as a convenience feature. This same log message could be printed by anything that's connected to the uart on the other side.
The exact format of this log message is not fixed and could change.
$ busctl list ... xyz.openbmc_project.Console.host1 926 obmc-console-server root ... xyz.openbmc_project.Console.host2 926 obmc-console-server root ... ...
$ busctl tree xyz.openbmc_project.Console.host2 └─ /xyz └─ /xyz/openbmc_project └─ /xyz/openbmc_project/console └─ /xyz/openbmc_project/console/host1 └─ /xyz/openbmc_project/console/host2 $ busctl tree xyz.openbmc_project.Console.host1 └─ /xyz └─ /xyz/openbmc_project └─ /xyz/openbmc_project/console └─ /xyz/openbmc_project/console/host1 └─ /xyz/openbmc_project/console/host2
$ busctl introspect xyz.openbmc_project.Console.host1 /xyz/openbmc_project/console/host1 NAME TYPE SIGNATURE RESULT/VALUE FLAGS org.freedesktop.DBus.Introspectable interface - - - .Introspect method - s - org.freedesktop.DBus.Peer interface - - - .GetMachineId method - s - .Ping method - - - org.freedesktop.DBus.Properties interface - - - .Get method ss v - .GetAll method s a{sv} - .Set method ssv - - .PropertiesChanged signal sa{sv}as - - xyz.openbmc_project.Console.Access interface - - - .Connect method - h -
+--------------------+ | server.conf | +--------------------+ | | | | +----+----+ +-----+ +-------+ | | | | | | | | +-------+ +-------+ | +-----+ UART1 | +-----------------------------------+ | | | | | | | | | | | xyz.openbmc_project.Console.host1 +-----+ +-----+ ttyS0 +-----+ UART0 +-----+ | +-------+ +-----------------------------------+ | | | | | | | | | obmc | +-------+ +-------+ | | | console | | MUX | | server | +-------+ | | +-----------------------------------+ | | | | | | | xyz.openbmc_project.Console.host2 +-----+ +-------------------+ GPIO +-----+ | +-------+ +-----------------------------------+ | | | | | | | | | | +-------+ | +-----+ UART2 | | | | | | | +----+----+ +-----+ +-------+