227 lines
9.3 KiB
ReStructuredText
227 lines
9.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=============================================
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CoreSight Embedded Cross Trigger (CTI & CTM).
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=============================================
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:Author: Mike Leach <mike.leach@linaro.org>
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:Date: November 2019
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Hardware Description
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--------------------
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The CoreSight Cross Trigger Interface (CTI) is a hardware device that takes
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individual input and output hardware signals known as triggers to and from
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devices and interconnects them via the Cross Trigger Matrix (CTM) to other
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devices via numbered channels, in order to propagate events between devices.
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e.g.::
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0000000 in_trigs :::::::
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0 C 0----------->: : +======>(other CTI channel IO)
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0 P 0<-----------: : v
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0 U 0 out_trigs : : Channels ***** :::::::
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0000000 : CTI :<=========>*CTM*<====>: CTI :---+
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####### in_trigs : : (id 0-3) ***** ::::::: v
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# ETM #----------->: : ^ #######
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# #<-----------: : +---# ETR #
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####### out_trigs ::::::: #######
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The CTI driver enables the programming of the CTI to attach triggers to
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channels. When an input trigger becomes active, the attached channel will
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become active. Any output trigger attached to that channel will also
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become active. The active channel is propagated to other CTIs via the CTM,
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activating connected output triggers there, unless filtered by the CTI
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channel gate.
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It is also possible to activate a channel using system software directly
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programming registers in the CTI.
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The CTIs are registered by the system to be associated with CPUs and/or other
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CoreSight devices on the trace data path. When these devices are enabled the
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attached CTIs will also be enabled. By default/on power up the CTIs have
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no programmed trigger/channel attachments, so will not affect the system
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until explicitly programmed.
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The hardware trigger connections between CTIs and devices is implementation
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defined, unless the CPU/ETM combination is a v8 architecture, in which case
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the connections have an architecturally defined standard layout.
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The hardware trigger signals can also be connected to non-CoreSight devices
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(e.g. UART), or be propagated off chip as hardware IO lines.
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All the CTI devices are associated with a CTM. On many systems there will be a
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single effective CTM (one CTM, or multiple CTMs all interconnected), but it is
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possible that systems can have nets of CTIs+CTM that are not interconnected by
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a CTM to each other. On these systems a CTM index is declared to associate
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CTI devices that are interconnected via a given CTM.
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Sysfs files and directories
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---------------------------
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The CTI devices appear on the existing CoreSight bus alongside the other
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CoreSight devices::
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>$ ls /sys/bus/coresight/devices
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cti_cpu0 cti_cpu2 cti_sys0 etm0 etm2 funnel0 replicator0 tmc_etr0
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cti_cpu1 cti_cpu3 cti_sys1 etm1 etm3 funnel1 tmc_etf0 tpiu0
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The ``cti_cpu<N>`` named CTIs are associated with a CPU, and any ETM used by
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that core. The ``cti_sys<N>`` CTIs are general system infrastructure CTIs that
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can be associated with other CoreSight devices, or other system hardware
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capable of generating or using trigger signals.::
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>$ ls /sys/bus/coresight/devices/etm0/cti_cpu0
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channels ctmid enable nr_trigger_cons mgmt power powered regs
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connections subsystem triggers0 triggers1 uevent
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*Key file items are:-*
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* ``enable``: enables/disables the CTI. Read to determine current state.
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If this shows as enabled (1), but ``powered`` shows unpowered (0), then
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the enable indicates a request to enabled when the device is powered.
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* ``ctmid`` : associated CTM - only relevant if system has multiple CTI+CTM
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clusters that are not interconnected.
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* ``nr_trigger_cons`` : total connections - triggers<N> directories.
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* ``powered`` : Read to determine if the CTI is currently powered.
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*Sub-directories:-*
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* ``triggers<N>``: contains list of triggers for an individual connection.
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* ``channels``: Contains the channel API - CTI main programming interface.
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* ``regs``: Gives access to the raw programmable CTI regs.
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* ``mgmt``: the standard CoreSight management registers.
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* ``connections``: Links to connected *CoreSight* devices. The number of
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links can be 0 to ``nr_trigger_cons``. Actual number given by ``nr_links``
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in this directory.
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triggers<N> directories
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~~~~~~~~~~~~~~~~~~~~~~~
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Individual trigger connection information. This describes trigger signals for
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CoreSight and non-CoreSight connections.
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Each triggers directory has a set of parameters describing the triggers for
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the connection.
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* ``name`` : name of connection
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* ``in_signals`` : input trigger signal indexes used in this connection.
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* ``in_types`` : functional types for in signals.
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* ``out_signals`` : output trigger signals for this connection.
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* ``out_types`` : functional types for out signals.
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e.g::
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>$ ls ./cti_cpu0/triggers0/
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in_signals in_types name out_signals out_types
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>$ cat ./cti_cpu0/triggers0/name
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cpu0
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>$ cat ./cti_cpu0/triggers0/out_signals
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0-2
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>$ cat ./cti_cpu0/triggers0/out_types
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pe_edbgreq pe_dbgrestart pe_ctiirq
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>$ cat ./cti_cpu0/triggers0/in_signals
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0-1
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>$ cat ./cti_cpu0/triggers0/in_types
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pe_dbgtrigger pe_pmuirq
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If a connection has zero signals in either the 'in' or 'out' triggers then
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those parameters will be omitted.
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Channels API Directory
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~~~~~~~~~~~~~~~~~~~~~~
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This provides an easy way to attach triggers to channels, without needing
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the multiple register operations that are required if manipulating the
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'regs' sub-directory elements directly.
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A number of files provide this API::
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>$ ls ./cti_sys0/channels/
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chan_clear chan_inuse chan_xtrigs_out trigin_attach
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chan_free chan_pulse chan_xtrigs_reset trigin_detach
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chan_gate_disable chan_set chan_xtrigs_sel trigout_attach
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chan_gate_enable chan_xtrigs_in trig_filter_enable trigout_detach
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trigout_filtered
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Most access to these elements take the form::
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echo <chan> [<trigger>] > /<device_path>/<operation>
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where the optional <trigger> is only needed for trigXX_attach | detach
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operations.
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e.g.::
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>$ echo 0 1 > ./cti_sys0/channels/trigout_attach
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>$ echo 0 > ./cti_sys0/channels/chan_set
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Attaches trigout(1) to channel(0), then activates channel(0) generating a
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set state on cti_sys0.trigout(1)
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*API operations*
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* ``trigin_attach, trigout_attach``: Attach a channel to a trigger signal.
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* ``trigin_detach, trigout_detach``: Detach a channel from a trigger signal.
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* ``chan_set``: Set the channel - the set state will be propagated around
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the CTM to other connected devices.
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* ``chan_clear``: Clear the channel.
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* ``chan_pulse``: Set the channel for a single CoreSight clock cycle.
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* ``chan_gate_enable``: Write operation sets the CTI gate to propagate
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(enable) the channel to other devices. This operation takes a channel
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number. CTI gate is enabled for all channels by default at power up. Read
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to list the currently enabled channels on the gate.
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* ``chan_gate_disable``: Write channel number to disable gate for that
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channel.
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* ``chan_inuse``: Show the current channels attached to any signal
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* ``chan_free``: Show channels with no attached signals.
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* ``chan_xtrigs_sel``: write a channel number to select a channel to view,
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read to show the selected channel number.
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* ``chan_xtrigs_in``: Read to show the input triggers attached to
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the selected view channel.
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* ``chan_xtrigs_out``:Read to show the output triggers attached to
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the selected view channel.
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* ``trig_filter_enable``: Defaults to enabled, disable to allow potentially
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dangerous output signals to be set.
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* ``trigout_filtered``: Trigger out signals that are prevented from being
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set if filtering ``trig_filter_enable`` is enabled. One use is to prevent
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accidental ``EDBGREQ`` signals stopping a core.
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* ``chan_xtrigs_reset``: Write 1 to clear all channel / trigger programming.
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Resets device hardware to default state.
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The example below attaches input trigger index 1 to channel 2, and output
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trigger index 6 to the same channel. It then examines the state of the
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channel / trigger connections using the appropriate sysfs attributes.
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The settings mean that if either input trigger 1, or channel 2 go active then
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trigger out 6 will go active. We then enable the CTI, and use the software
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channel control to activate channel 2. We see the active channel on the
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``choutstatus`` register and the active signal on the ``trigoutstatus``
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register. Finally clearing the channel removes this.
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e.g.::
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.../cti_sys0/channels# echo 2 1 > trigin_attach
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.../cti_sys0/channels# echo 2 6 > trigout_attach
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.../cti_sys0/channels# cat chan_free
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0-1,3
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.../cti_sys0/channels# cat chan_inuse
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2
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.../cti_sys0/channels# echo 2 > chan_xtrigs_sel
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.../cti_sys0/channels# cat chan_xtrigs_trigin
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1
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.../cti_sys0/channels# cat chan_xtrigs_trigout
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6
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.../cti_sys0/# echo 1 > enable
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.../cti_sys0/channels# echo 2 > chan_set
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.../cti_sys0/channels# cat ../regs/choutstatus
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0x4
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.../cti_sys0/channels# cat ../regs/trigoutstatus
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0x40
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.../cti_sys0/channels# echo 2 > chan_clear
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.../cti_sys0/channels# cat ../regs/trigoutstatus
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0x0
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.../cti_sys0/channels# cat ../regs/choutstatus
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0x0
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