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CNMAGIC(9) NetBSD Kernel Developer's Manual CNMAGIC(9)
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cn_init_magic, cn_trap, cn_isconsole, cn_check_magic, cn_destroy_magic,
cn_set_magic, cn_get_magic -- console magic key sequence management
cn_check_magic(dev_t dev, int k, cnm_state_t *cnms);
cn_get_magic(char *magic, int len);
The NetBSD console magic key sequence management framework is designed to
provide flexible methods to set, change, and detect magic key sequences
on console devices and break into the debugger or ROM monitor with a min-
imum of interrupt latency.
Drivers that generate console input should make use of these routines. A
different cnm_state_t should be used for each separate input stream.
Multiple devices that share the same input stream, such as USB keyboards,
can share the same cnm_state_t. Once a cnm_state_t is allocated, it
should be initialized with cn_init_magic() so it can be used by
cn_check_magic(). If a driver thinks it might be the console input
device it can set the magic sequence with cn_set_magic() to any arbitrary
string. Whenever the driver receives input, it should call
cn_check_magic() to process the data and determine whether the magic
sequence has been hit.
The magic key sequence can be accessed through the hw.cnmagic sysctl
variable. This is the raw data and may be keycodes rather than processed
characters, depending on the console device.
The following functions describe the console magic interface.
Initialize the console magic state pointed to by cnm to a usable
Trap into the kernel debugger or ROM monitor. By default this
routine is defined to be console_debugger() but can be overridden
in MI header files.
Determine whether a given dev is the system console. This macro
tests to see if dev is the same as cn_tab->cn_dev but can be
overridden in MI header files.
cn_check_magic(dev, k, cnms)
All input should be passed through cn_check_magic() so the state
machine remains in a consistent state. cn_check_magic() calls
cn_isconsole() with dev to determine if this is the console. If
that returns true then it runs the input value k through the
state machine. If the state machine completes a match of the
current console magic sequence cn_trap() is called. Some input
may need to be translated to state machine values such as the
serial line BREAK sequence.
This should be called once what cnms points to is no longer
cn_set_magic() encodes a nul terminated arbitrary string into
values that can be used by the state machine and installs it as
the global magic sequence. The escape sequence is character
value 0x27 and can be used to encode special values:
0x27 The literal value 0x27.
0x01 Serial BREAK sequence.
0x02 Nul character.
Returns 0 on success or a non-zero error value.
Extract the current magic sequence from the state machine and
return up to len bytes of it in the buffer pointed to by magic.
It uses the same encoding accepted by cn_set_magic(). Returns 0
on success or a non-zero error value.
ddb(4), sysctl(8), cons(9)
The NetBSD console magic key sequence management framework first appeared
in NetBSD 1.6.
The NetBSD console magic key sequence management framework was designed
and implemented by Eduardo Horvath <eeh@NetBSD.org>.
NetBSD 9.0 July 7, 2019 NetBSD 9.0