Documentation/trace/coresight/coresight-etm4x-reference.rst

Source file repositories/reference/linux-study-clean/Documentation/trace/coresight/coresight-etm4x-reference.rst

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Documentation/trace/coresight/coresight-etm4x-reference.rst
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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===============================================
ETMv4 sysfs linux driver programming reference.
===============================================

    :Author:   Mike Leach <mike.leach@linaro.org>
    :Date:     October 11th, 2019

Supplement to existing ETMv4 driver documentation.

Sysfs files and directories
---------------------------

Root: ``/sys/bus/coresight/devices/etm<N>``


The following paragraphs explain the association between sysfs files and the
ETMv4 registers that they effect. Note the register names are given without
the ‘TRC’ prefix.

----

:File:            ``mode`` (rw)
:Trace Registers: {CONFIGR + others}
:Notes:
    Bit select trace features. See ‘mode’ section below. Bits
    in this will cause equivalent programming of trace config and
    other registers to enable the features requested.

:Syntax & eg:
    ``echo bitfield > mode``

    bitfield up to 32 bits setting trace features.

:Example:
    ``$> echo 0x012 > mode``

----

:File:            ``reset`` (wo)
:Trace Registers: All
:Notes:
    Reset all programming to trace nothing / no logic programmed.

:Syntax:
    ``echo 1 > reset``

----

:File:            ``enable_source`` (wo)
:Trace Registers: PRGCTLR, All hardware regs.
:Notes:
    - > 0 : Programs up the hardware with the current values held in the driver
      and enables trace.

    - = 0 : disable trace hardware.

:Syntax:
    ``echo 1 > enable_source``

----

:File:            ``cpu`` (ro)
:Trace Registers: None.
:Notes:
    CPU ID that this ETM is attached to.

:Example:
    ``$> cat cpu``

    ``$> 0``

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