Difference between revisions of "Zephyr driver demo"

Revision as of 16:38, 13 September 2021

Zephyr Driver and Separate Demo

- OVERVIEW - Here list and begin to describe key, salient features of a Zephyr RTOS based driver and separately build-able demo to exercise given driver. Driver for first version 0p0 is "out of tree", in other words outside of Zephyr project's source tree.

^ Key Zephyr App Files

Move to refs:

 *  https://dev.w3.org/html5/html-author/charref   å
 *  https://meta.wikimedia.org/wiki/Table_background_colors
 
 *  https://community.jaredwolff.com/d/4-nrf-cloud-agps-sample-no-gps-data/6

Key files in the two parts of Zephyr out-of-tree driver and demonstrating app:

demo (app)
   ¦
CMakeLists.txt  <- set toolchain variant and toolchain path
Kconfig         <- refers to Zephyr top level Kconfig
west.yml        <- chooses SDK, driver projects (1)

driver
   ¦
drivers/
dts/bindings/
include/
zephyr/
   ¦
   +--module.yml
CMakeLists.txt  <- · add subdirs when given drivers enabled,
                   ▸ add include dirs holding header files
Kconfig         <- · refers to Kconfig in child 'drivers' directory
README.md

Note: the out-of-tree driver has a zephyr/module.yml dir and file. The zephyr app does not.

All the more that is in Jared Wolff's AQW demo:

ted@localhost:~/projects/embedded/ncs/zephyr/samples/sandbox-de-ted/jared-wolff/demo$ tree -R
.
├── boards
│   ├── nrf52840dk_nrf52840.conf
│   └── nrf52840dk_nrf52840.overlay
├── CMakeLists.txt
├── Kconfig
├── prj.conf
├── prj.debug.conf
├── prj.release.conf
├── README.md
├── src
│   └── main.c
├── west.yml
└── z--build-messages-001--first-build.txt

2 directories, 11 files

^ Supporting Linux Commands

^ Useful Commands To Manage Zephyr Project Details

Command available on Ubuntu hosts to effectively locate Zephyr RTOS project installations:

   ted@localhost:~/projects/embedded$ locate VERSION | grep 'ION$'

Committing changes to Zephyr app dependencies which are secondary git repositories linked and locally updated via `west` and the given project's west.yml manifest file:

Command line excerpt - switch from git project detached head to 'main' branch of development, and merge:

 1053  git status
 1054  git checkout main
 1055  git merge c601129

In the above excerpt the argument to `git merge` is the start of the commit hash of the detached head commit history which, for some reason `west` meta-tool creates whenever developer issues `west update` in a local Zephyr application project. The commit hash here is arbitrary. It will be different pretty much every time a developer updates local code from remote repositories. Important to make a note of most recent hash before checking out a named branch!

^ Configuration and Set Up Steps

^ New Zephyr app `west init` and `west update`

Upon, after first invocation of `west init && west update` in a newly cloned Zephyr app project, files pulled down include:

ted@localhost:~/projects/sandbox-2/kionix-driver-demo$ ls
bootloader  modules  tools  west.yml  zephyr
ted@localhost:~/projects/sandbox-2/kionix-driver-demo$ git status .
On branch main
Your branch is up to date with 'origin/main'.

Untracked files:
  (use "git add <file>..." to include in what will be committed)
	.west/
	bootloader/
	modules/
	tools/
	zephyr/

nothing added to commit but untracked files present (use "git add" to track)

The west.yml file specifies an ncs software development kit, which include Zephyr and bootloader. All the directories and files above not tracked by git were downloaded by the `west` meta-tool. So this non-tracking is consistent with the way `west` works, and brings in files to a `west manifest` project that is itself under git control.

^ Zephyr Overlay Files and Device Node Label Strings

Given a meta-compiled symbol assignment which takes a DTS node 'label' string, best to avoid use of minus character in these labels:

ted@ubuntu-vm-0p2:~/embedded/z1-sandbox-2021-08-26/kionix-driver-demo$ grep -nr KX132-1211 ./*

Binary file ./boards/.sparkfun_thing_plus_nrf9160.overlay.swp matches
./boards/nrf9160dk_nrf9160ns.overlay:14:                label = "KX132-1211";
./boards/sparkfun_thing_plus_nrf9160.overlay:15:                label = "KX132-1211";
./boards/nrf9160dk_nrf9160.overlay:14:                label = "KX132-1211";
./build/mcuboot/zephyr/.config:421:# KX132-1211 driver
./build/mcuboot/zephyr/.config:423:# end of KX132-1211 driver
./build/zephyr/include/generated/autoconf.h:61:#define CONFIG_KX132_1211_DRV_NAME "KX132-1211"
./build/zephyr/include/generated/devicetree_unfixed.h:6118:#define DT_N_S_soc_S_peripheral_50000000_S_i2c_9000_S_kx132_1211_1f_P_label "KX132-1211"
./build/zephyr/sparkfun_thing_plus_nrf9160.dts.pre.tmp:645:                label = "KX132-1211";
./build/zephyr/zephyr.dts:253:                                  label = "KX132-1211";
./build/zephyr/.config:346:# KX132-1211 driver
./build/zephyr/.config:349:CONFIG_KX132_1211_DRV_NAME="KX132-1211"
./build/zephyr/.config:350:# end of KX132-1211 driver
Binary file ./build/zephyr/edt.pickle matches

ted@ubuntu-vm-0p2:~/embedded/z1-sandbox-2021-08-26/kionix-driver-demo$

^ Zephyr Project Uniform Sensor API

Zephyr Project's notion of sensor channels for reading back data in given units is important. Here is a starting point documentation on this topic:

• https://docs.zephyrproject.org/1.14.1/reference/peripherals/sensor.html

Many of the most important programmatic elements of Zephyr's sensor API are defined in sensors.h, which includes C structs, an enum of Zephyr supported "sensor channels", function prototypes and some other programmatic API features. As of 2021-09-13 Zephyr's v2.6 release tag holds this header file at the URL:

https://github.com/zephyrproject-rtos/zephyr/blob/v2.6-branch/include/drivers/sensor.h

One thing that's becoming more clear, Zephyr's macros and build process create some level of indirection between a developer's custom code calls to sensor API functions like sample_fetch() and channel_get() and the functions themselves. The Zephyr source tree, for example, we can search for patterns matching these API routine names. We'll find prototypes for them, but no definitions even though their names appear generic, e.g. their names do not indicate that they're written for a given sensor.

Through the "macros magic" of Zephyr RTOS build process a developer's specific sensor driver code is connected to, and or ultimately populates the API functions fetch, get, trigger, etc which developer project code calls to configure and obtain readings from sensors. For this reason the follow section of this wiki page, "Chain of Calls..." cannot show a more traditional series of C language calls from a program's nominal starting point at int main() up to the deepest stack frame which holds a sensor's value ready to store or write to UART or file.

^ Programmatic Chain From main Function To Print Sensor Readings

This section aims to capture a clear sequence of C-based routines and routine calls, from int main() to an effective printf() type of function in a Zephyr RTOS application. In part this wiki page section is motivated by Zephyr's multiple ways of obtaining programmatic handles or pointers to devices, and what appear to be at least two distinct but strictly guided ways of connecting app code to a sensor driver API.

Though we cannot build and test it for lack of specific development board, Jared Wolff's Air Quality Wing driver demo we assume compiles and runs correctly given Jared's sharing of the project, and addition of two sensors in the past two weeks. We'll use this as a starting point looking at 'main.c' and 'inc main()' there . . .

err = aqw_init(sensors, ARRAY_SIZE(sensors), sensor_cb);

Hmm we haven't searched very far and already find that 'device_get_binding()' is not directly defined seemingly anywhere in Zephyr 2.6.0 sources. In zephyr/kernel/device.c there are defs for const struct device *z_impl_device_get_binding() and static inline const struct device *z_vrfy_device_get_binding().

./kernel/device.c:104:const struct device *z_impl_device_get_binding(const char *name)
./kernel/device.c:136:static inline const struct device *z_vrfy_device_get_binding(const char *name)

Some related information and explanation of the two ways to obtain handles/pointers to devices in Zephyr app in this document:

• https://docs.zephyrproject.org/latest/guides/dts/howtos.html#get-devicetree-outputs
• https://docs.zephyrproject.org/latest/guides/dts/howtos.html#get-a-struct-device-from-a-devicetree-node

Research and review also zephyr/include/device.h header file section with comment block:

 .
 .
 .
122 /**
123  * @def DEVICE_DEFINE
124  *
125  * @brief Create device object and set it up for boot time initialization,
126  * with the option to pm_control. In case of Device Idle Power
127  * Management is enabled, make sure the device is in suspended state after
128  * initialization.
129  *
130  * @details This macro defines a device object that is automatically
131  * configured by the kernel during system initialization. Note that
132  * devices set up with this macro will not be accessible from user mode
133  * since the API is not specified;
134  *
135  * @param dev_name Device name. This must be less than Z_DEVICE_MAX_NAME_LEN
136  * characters (including terminating NUL) in order to be looked up from user
137  * mode with device_get_binding().
138  *
 .
 .
 .

Tracing the "sensor fetch" command in Jared Wolff's Air Quality Wing Demo, eventually get to 'sensor_channel_get()' function which does not appear to be defined anywhere in Zephyr sources:

cpguest@ubuntu-vm-0p2:~/embedded/z1-sandbox-2021-08-26/zephyr/drivers$ grep -nr sensor_channel_get ./*
./clock_control/nrf_clock_calibration.c:182:            rc = sensor_channel_get(temp_sensor, SENSOR_CHAN_DIE_TEMP,
./sensor/sensor_shell.c:106:    err = sensor_channel_get(dev, i, value);
./sensor/shell_battery.c:39:            err = sensor_channel_get(dev, chan, val);
./sensor/sensor_handlers.c:50:static inline int z_vrfy_sensor_channel_get(const struct device *dev,
./sensor/sensor_handlers.c:56:  return z_impl_sensor_channel_get((const struct device *)dev, chan,
./sensor/sensor_handlers.c:59:#include <syscalls/sensor_channel_get_mrsh.c>
cpguest@ubuntu-vm-0p2:~/embedded/z1-sandbox-2021-08-26/zephyr/drivers$

^ AQW Example Sensor Structs and Data Fetch Functions

Air Quality Wing code by Jared Wolff of CircuitDojo. AQW header file showing sensor types enumeration and two key structure:

• https://github.com/circuitdojo/air-quality-wing-zephyr-drivers/blob/main/include/aqw.h

Air Quality Wing 'lib' source file, good reference for sensor structure syntax and use:

• https://github.com/circuitdojo/air-quality-wing-zephyr-drivers/blob/main/lib/aqw.c