AM6442: Is there a Linux (A53) driver for the EQEP peripheral in AM64X

Jim Mrowca

Part Number: AM6442

I saw the AM62x posting from earlier this year? Has anyone in TI did a 64 bit Linux (A53 core) driver for the EQEP periphery in AM6x ? (I am asking for AM64x)

10 months ago

0 Nick Saulnier 10 months ago

TI__Guru* 93105 points

Hello Jim,

Good question. We added an EQEP driver (in SDK 9.1 I believe), and when I check SDK 9.2 I see the eqep devicetree node defined for AM62x, AM62Ax, AM62Px, and AM64x.

However, I do NOT see any documentation in the Linux SDK docs, and the AM64x SW Build Sheet for SDK 9.2 still lists EQEP as "not enabled in Linux".

So my assumption is that the driver exists and was tested on AM64x, and we just have not finished adding the documentation. I'll check with the developer, and file some internal tickets to get the documentation updated.

Regards,

Nick

0 Nick Saulnier 10 months ago in reply to Nick Saulnier

TI__Guru* 93105 points

Actually, it looks like the driver might only be available starting in SDK 9.2.

Regards,

Nick

0 Nick Saulnier 10 months ago in reply to Nick Saulnier

TI__Guru* 93105 points

edited May 22, 2024: the final version of the documentation has been pushed. See https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1363410/am6442-is-there-a-linux-a53-driver-for-the-eqep-peripheral-in-am64x/5210141#5210141

Final followup, the documentation got stalled out in the draft/review state. I'll include the source code to generate the documentation here. There might be issues, since this is not a "finished" product.

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EQEP
---------------------------------
.. rubric:: Introduction
   :name: introduction-linux-eqep
Linux has support for EQEP (enhanced Quadature Encoder Pulse).
EQEP channels can be used to interface with rotary encoder hardware.
#. AM62x SK: EQEP0: k3-am62x-sk-eqep.dtso
#. AM62Ax SK: EQEP0: k3-am62x-sk-eqep.dtbo
#. AM64x SK: EQEP0: k3-am642-sk.dts
#. AM62p SK: EQEP0: k3-am62p5-sk-eqep.dtso
|
.. rubric:: Kernel Configuration
   :name: driver-configuration-eqep
.. rubric:: Enable the eHRPWM driver
   :name: enable-the-eqep-driver
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

EQEP
---------------------------------

.. rubric:: Introduction
:name: introduction-linux-eqep

Linux has support for EQEP (enhanced Quadature Encoder Pulse).
EQEP channels can be used to interface with rotary encoder hardware.

#. AM62x SK: EQEP0: k3-am62x-sk-eqep.dtso
#. AM62Ax SK: EQEP0: k3-am62x-sk-eqep.dtbo
#. AM64x SK: EQEP0: k3-am642-sk.dts
#. AM62p SK: EQEP0: k3-am62p5-sk-eqep.dtso

.. rubric:: Kernel Configuration
:name: driver-configuration-eqep

.. rubric:: Enable the eHRPWM driver
:name: enable-the-eqep-driver

.. code-block:: console

Device Drivers --->
<M> Counter support --->
<M> TI eQEP counter driver

.. note::

EQEP driver should be enabled by default as a module in TI Linux kernel.

.. rubric:: Driver Usage
:name: driver-usage-eqep

.. rubric:: Using EQEP with the sysfs interface
:name: using-eqep-with-sysfs-interface

Several sysfs attributes are generated by the Generic Counter interface, and reside under the
/sys/bus/counter/devices/counterX directory, where X is to the respective counter device id.

Please see Documentation/ABI/testing/sysfs-bus-counter for detailed information on each Generic
Counter interface sysfs attribute.

Through these sysfs attributes, programs and scripts may interact with the Generic Counter paradigm
Counts, Signals, and Synapses of respective counter devices.

- **Example**

.. code-block:: console

root@am62xx-evm:/sys/bus/counter/devices/counter0/count0# echo 0xff > ceiling
root@am62xx-evm:/sys/bus/counter/devices/counter0/count0# cat ceiling
255
root@am62xx-evm:/sys/bus/counter/devices/counter0/count0# echo 1 > enable
root@am62xx-evm:/sys/bus/counter/devices/counter0/count0# cat count

**Character device nodes**

Counter character device nodes are created under the /dev directory as counterX, where X is the respective counter device id.

.. code-block:: console

$ ls /dev/counter*
/dev/counter0

**Counter Events**

Please read the Generic counter API doc to implement events:

- https://docs.kernel.org/driver-api/generic-counter.html

Regards,

Nick

0 Nick Saulnier 10 months ago in reply to Nick Saulnier

TI__Guru* 93105 points

Additional information here: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1290183/am625-eqep

0 Jim Mrowca 10 months ago in reply to Nick Saulnier

Genius 3369 points

Nick: did that implementation go through some form of regression testing?

Would it be fairly simple to take the MCU+ SDK's eqep_capture example on the R5 in FreeRTOS and morph that into Linuc on the A53?

thanks

Jim

0 Nick Saulnier 10 months ago in reply to Jim Mrowca

TI__Guru* 93105 points

Hello Jim,

The code was tested on AM64x, but I am not sure exactly what tests were run. I can ask the developer if needed.

I cannot comment on porting MCU+ SDK EQEP example to Linux. I would start with trying to run an example in Linux as per the draft documentation above, and if things do not work as expected you can ask followup questions:
https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1363410/am6442-is-there-a-linux-a53-driver-for-the-eqep-peripheral-in-am64x/5205034#5205034

Regards,

Nick

0 Jim Mrowca 10 months ago in reply to Nick Saulnier

Genius 3369 points

Nick - we should ask the developer to disclose what tests were run - that way you can ascertain what may be necessary and sufficient to qualify for the Linux representation to be a "finished" product in AM6x. I suspect someone from Houston Stafford (Paula Carrillo?) should be involved?

Meanwhile I will look at the representation that you had supplied.

thanks

Jim

+1 Nick Saulnier 10 months ago in reply to Jim Mrowca

TI__Guru* 93105 points

Hello Jim,

Paula is focused more on the MCU+ side of things, I'll continue handling the Linux EQEP questions for now.

The developer told me since this driver is so new, they are still working on setting up the EQEP test infrastructure for future SDK releases. I would expect that in the future, you will be able to see test outputs for the CICD snapshots here:
https://software-dl.ti.com/cicd-report/linux/index.html?section=platform&platform=am64xx

They also finished merging in the EQEP driver documentation for the Linux SDK docs last night. I'll attach the updated source code here, since I'm not sure if the AM64x SDK 9.2 docs will be regenerated again in the near term, or if this update will show up for the first time in SDK 10.0 documentation:

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EQEP
----
.. rubric:: Introduction
   :name: introduction-linux-eqep
Linux has support for EQEP (Enhanced Quadature Encoder Pulse).
EQEP channels can be used to interface with rotary encoder hardware.
.. ifconfig:: CONFIG_part_variant in ('AM62X', 'AM62AX')
    - AM62x SK: EQEP0: k3-am62x-sk-eqep.dtso
.. ifconfig:: CONFIG_part_variant in ('AM64X')
    - AM64x SK: EQEP0: k3-am642-sk.dts
.. ifconfig:: CONFIG_part_variant in ('AM62PX')
    - AM62p SK: EQEP0: k3-am62p5-sk-eqep.dtso
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

EQEP
----

.. rubric:: Introduction
   :name: introduction-linux-eqep

Linux has support for EQEP (Enhanced Quadature Encoder Pulse).
EQEP channels can be used to interface with rotary encoder hardware.

.. ifconfig:: CONFIG_part_variant in ('AM62X', 'AM62AX')

	- AM62x SK: EQEP0: k3-am62x-sk-eqep.dtso

.. ifconfig:: CONFIG_part_variant in ('AM64X')

	- AM64x SK: EQEP0: k3-am642-sk.dts

.. ifconfig:: CONFIG_part_variant in ('AM62PX')

	- AM62p SK: EQEP0: k3-am62p5-sk-eqep.dtso

.. rubric:: Kernel Configuration
   :name: driver-configuration-eqep

Using menuconfig, enable the following driver:

.. code-block:: console

   Device Drivers --->
       <M> Counter support  --->
         <M> TI eQEP counter driver

.. note::

   EQEP driver should be enabled by default as a kernel module in TI Linux kernel.

.. rubric:: Features supported in TI SDK
   :name: features-supported-eqep

- position
- overflow/underflow events
- direction
- unit timer
- latched position
- edge capture

.. rubric:: Using eQEP with SYSFS interface
   :name: sysfs-interface-eqep

Several sysfs attributes are generated by the Generic Counter interface, and reside under
the :file:`/sys/bus/counter/devices/counterX` directory, where X is to the respective counter
device id.

Please see the counter sysfs documentation `upstream <https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-counter>`__
or in TI Linux kernel :file:`/Documentation/ABI/testing/sysfs-bus-counter` for detailed information on each
generic counter interface sysfs attribute.

Through these sysfs attributes, programs and scripts may interact with the Generic Counter paradigm
Counts, Signals, and Synapses of respective counter devices.

The following sysfs atributes can be found in :file:`/sys/bus/counter/devices/counterX` in TI SDK:

- countY/ceiling
- countY/count
- countY/direction
- countY/enable
- countY/function
- countY/latched_count
- countY/signal0_action
- countY/signal1_action
- edge_capture_unit_enable
- edge_capture_unit_latched_period
- edge_capture_unit_max_period
- edge_capture_unit_prescaler
- latch_mode
- unit_timer_enable
- unit_timer_period
- unit_timer_time

.. rubric:: Character device nodes
   :name: character-device-nodes-eqep

Counter character device nodes are created under the /dev directory as counterX, where X is the respective counter device id.

.. code-block:: console

   $ ls /dev/counter*
   /dev/counter0

.. rubric:: Counter Events
   :name: counter-events

Please read the generic counter API `upstream <https://docs.kernel.org/driver-api/generic-counter.html>`__ or in
TI Linux kernel :file:`/Documentation/driver-api/generic-counter.rst` documentation to implement events:

.. rubric:: Test eQEP on AM62x SK
   :name: test-eqep-am62x

+------------------------------------------+---------------------------------------------------------+
| .. Image:: /images/am62x_sk_eqep.jpg     | .. Image:: /images/am62x_sk_rotary_encoder_breakout.jpg |
|       :width: 380px                      |       :width: 380px                                     |
|       :align: center                     |       :align: center                                    |
+------------------------------------------+---------------------------------------------------------+
| AM62x SK & rotary encoder breakout board | Example Diligent rotary encoder breakout board          |
+------------------------------------------+---------------------------------------------------------+

The example rotary encoder breakout board used in this example can be found `here <https://www.digikey.com/en/products/detail/digilent,-inc./410-117/4090075?>`__.

The following is an example for testing eQEP using sysfs interface:

.. code-block:: console

	root@am62xx-evm:~# echo 0xff > /sys/bus/counter/devices/counter0/count0/ceiling 
	root@am62xx-evm:~# cat /sys/bus/counter/devices/counter0/count0/ceiling
	255
	root@am62xx-evm:~# echo 1 > /sys/bus/counter/devices/counter0/count0/enable 
	root@am62xx-evm:~# cat /sys/bus/counter/devices/counter0/count0/count
	0
	root@am62xx-evm:~# cat /sys/bus/counter/devices/counter0/count0/count
	92
	root@am62xx-evm:~# cat /sys/bus/counter/devices/counter0/count0/count
	148
	root@am62xx-evm:~# cat /sys/bus/counter/devices/counter0/count0/count
	188
	root@am62xx-evm:~# cat /sys/bus/counter/devices/counter0/count0/count
	252
	root@am62xx-evm:~# cat /sys/bus/counter/devices/counter0/count0/count
	12

Notice in this example that turning the rotary shaft encoder counterclockwise increases the count
until reaching the ceiling, then wraps around to zero and starts again. Also, turning the rotary
shaft encoder clockwise decreases the count.

Regards,

Nick

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AM6442: Is there a Linux (A53) driver for the EQEP peripheral in AM64X