u-boot/doc/README.serial_multi

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The support for multiple serial interfaces as implemented is mainly
intended to allow for modem dial-in / dial-out while still being able
to use a serial console on a (different) serial port.
MPC8XX Specific
===============
At the moment, the ports must be split on a SMC and a SCC port on a
8xx processor; other configurations are not (yet) supported.
Support for hardware handshake has not been implemented yet (but is
in the works).
*) The default console depends on the keys pressed:
- SMC if keys not pressed (modem not enabled)
- SCC if keys pressed (modem enabled)
*) The console can be switched to SCC by any of the following commands:
setenv stdout serial_scc
setenv stdin serial_scc
setenv stderr serial_scc
*) The console can be switched to SMC by any of the following commands:
setenv stdout serial_smc
setenv stdin serial_smc
setenv stderr serial_smc
*) If a file descriptor is set to "serial" then the current serial device
will be used which, in turn, can be switched by above commands.
*) The baudrate is the same for all serial devices. But it can be switched
just after switching the console:
setenv sout serial_scc; setenv baudrate 38400
After that press 'enter' at the SCC console. Note that baudrates <38400
are not allowed on LWMON with watchdog enabled (see CFG_BAUDRATE_TABLE in
include/configs/lwmon.h).
PPC4XX Specific
===============
*) The default console is UART0
*) The console can be switched to UART1 by any of the following commands:
setenv stdout serial1
setenv stderr serial1
setenv stdin serial1
*) The console can be switched to UART0 by any of the following commands:
setenv stdout serial0
setenv stderr serial0
setenv stdin serial0