Zephyr device driver model
Keywords: zephyr device drivers Zephyr device driver model Zephyr device drivers getting started
- OVERVIEW - Challenged by Zephyr's way of writing device drivers, capturing some notes here on a study of a Zephyr example project which talks to LIS2DH accelerometer on a Sparkfun Thing Plus board. Casting net wider for Zephyr device driver "How To" articles, find Jared Wolff's blog post:
Here is a link to a tutorial, part three of a series, which may be helpful:
Excerpt from Zephyr project drivers documentation:
-
Driver Data Structures
The device initialization macros populate some data structures at build time which are split into read-only and runtime-mutable parts. At a high level we have:
struct device {
const char *name;
const void *config;
const void *api;
void * const data;
};
Excerpt from file ~/ncs/zephyr/include/drivers/sensor.h:
382 /**
383 * @brief Set an attribute for a sensor
384 *
385 * @param dev Pointer to the sensor device
386 * @param chan The channel the attribute belongs to, if any. Some
387 * attributes may only be set for all channels of a device, depending on
388 * device capabilities.
389 * @param attr The attribute to set
390 * @param val The value to set the attribute to
391 *
392 * @return 0 if successful, negative errno code if failure.
393 */
394 __syscall int sensor_attr_set(const struct device *dev,
395 enum sensor_channel chan,
396 enum sensor_attribute attr,
397 const struct sensor_value *val);
398
399 static inline int z_impl_sensor_attr_set(const struct device *dev,
400 enum sensor_channel chan,
401 enum sensor_attribute attr,
402 const struct sensor_value *val)
403 {
404 const struct sensor_driver_api *api =
405 (const struct sensor_driver_api *)dev->api;
406
407 if (api->attr_set == NULL) {
408 return -ENOSYS;
409 }
410
411 return api->attr_set(dev, chan, attr, val);
412 }
413
From these two code excerpts the big question is, how is dev->api assigned in early configuring code for an I2C based sensor?
./include/drivers/sensor.h:61: SENSOR_CHAN_ACCEL_XYZ, . . . hmm, this is part of a large enumeration:
53 enum sensor_channel {
54 /** Acceleration on the X axis, in m/s^2. */
55 SENSOR_CHAN_ACCEL_X,
56 /** Acceleration on the Y axis, in m/s^2. */
57 SENSOR_CHAN_ACCEL_Y,
58 /** Acceleration on the Z axis, in m/s^2. */
59 SENSOR_CHAN_ACCEL_Z,
60 /** Acceleration on the X, Y and Z axes. */
61 SENSOR_CHAN_ACCEL_XYZ,
62 /** Angular velocity around the X axis, in radians/s. */
63 SENSOR_CHAN_GYRO_X,
64 /** Angular velocity around the Y axis, in radians/s. */
65 SENSOR_CHAN_GYRO_Y,
66 /** Angular velocity around the Z axis, in radians/s. */
67 SENSOR_CHAN_GYRO_Z,
68 /** Angular velocity around the X, Y and Z axes. */
69 SENSOR_CHAN_GYRO_XYZ,
.
.
.
edit point
ted@localhost:~/projects/embedded/ncs/zephyr/samples/z--sandbox/blink-plus-uart/build/zephyr/boards/arm/sparkfun_thing_plus_nrf9160$ nm -s libboards__arm__sparkfun_thing_plus_nrf9160.a
board.c.obj:
0000002c t $d
00000000 r $d
00000000 t $t
00000001 t board_sparkfun_thing_plus_nrf9160_init
00000000 r __init_sys_init_board_sparkfun_thing_plus_nrf9160_init0
U z_impl_device_get_binding
ted@localhost:~/projects/embedded/ncs/zephyr/samples/z--sandbox/blink-plus-uart/build/zephyr/boards/arm/sparkfun_thing_plus_nrf9160$
File noted:
ted@localhost:~/projects/embedded/ncs/zephyr/samples/z--sandbox/blink-plus-uart/build/zephyr/dev_handles.c
ted@localhost:~/projects/embedded/ncs/zephyr/samples/z--sandbox/blink-plus-uart/build/zephyr$ ls *.c dev_handles.c isr_tables.c ted@localhost:~/projects/embedded/ncs/zephyr/samples/z--sandbox/blink-plus-uart/build/zephyr$ ls *.h ls: cannot access '*.h': No such file or directory
Example project build directory noted, this dir auto-gen'd:
ted@localhost:~/projects/embedded/ncs/zephyr/samples/z--sandbox/blink-plus-uart/build/zephyr$ ls include/generated/ app_data_alignment.ld autoconf.h driver-validation.h otype-to-size.h snippets-ram-sections.ld snippets-sections.ld version.h app_smem_aligned.ld device_extern.h kobj-types-enum.h otype-to-str.h snippets-rodata.ld syscall_dispatch.c app_smem.ld devicetree_fixups.h ncs_version.h pm_config.h snippets-rom-start.ld syscall_list.h app_smem_unaligned.ld devicetree_unfixed.h offsets.h snippets-noinit.ld snippets-rwdata.ld syscalls
^ Kionix KX132
Useful datasheets and documents for Kionix accelerometer KX132-1211:
