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--- en:edu:zmitac:s2:aih:lab:nrf52gpio [2023/11/22 17:25] – [Tasks for the laboratory on GPIO] ktokarz
+++ en:edu:zmitac:s2:aih:lab:nrf52gpio [2025/11/14 10:59] (current) – [Tasks for the laboratory on GPIO] ktokarz
@@ Line 101: / Line 101: @@
   * **DT_NODE_HAS_STATUS** checks if the status of the node is OK.
 If the status is OK the label, the number of the pin, and flags are set as defined in the device tree. If not, all these elements are cleared. This may look like the overhead, but it is useful while we work with different hardware boards to prevent the compilation of the software for incompatible boards.
-The initial part of the code creates the structure which holds the parameters of the device and binds it with LED0 identifier. At the end, the device is configured according to parameters taken from the device tree.
+The initial part of the code creates the structure which holds the parameters of the device and binds it with the LED0 identifier. At the end, the device is configured according to parameters taken from the device tree.
-After configuration program jumps into the infinite while loop to blink LED every 1000 ms.
+After the configuration, the program jumps into the infinite while loop to blink the LED every 1000 ms.
 <code>
 /* ... */
@@ Line 134: / Line 134: @@
 }
 </code>
+===== Direct register use =====
+Using a device tree is universal but can be found somehow complex. To obtain the same results, certainly, with losing the portability of the program between different microcontrollers and hardware platforms, there is a possibility to write directly to registers of the microcontroller. We need to know what is the base address of the P0 port and offsets of the registers responsible for pin configuration and state. Also, the pin number where the LED is connected. The values are presented in the table 1.
+<table>
+<caption>"Values needed for the program with direst register use"</caption>
+^ base address ^ direction register ^ port register ^ pin number ^
+| 0x50000000 | 0x514 | 0x504 | 14 |
+</table>
+The program can look like this.
+<code>
+#include <kernel.h>
+#define SLEEP_TIME_MS	   1000
+#define P0_BASE_ADDR	   0x50000000
+#define GPIO_PORT_REG      0x504 //offset of the register for output state
+#define GPIO_DIRECTION_REG 0x514 //offset of the register for defining pin function
+#define PIN_NUMBER         14    //led1 on the nRF52840 DK board
+int main(void)
+{
+    volatile uint32_t *p0_dir_reg = (volatile uint32_t *) (P0_BASE_ADDR + GPIO_DIRECTION_REG);
+    *p0_dir_reg |= (1 << PIN_NUMBER);
+    volatile uint32_t *p0_port_reg = (volatile uint32_t *) (P0_BASE_ADDR + GPIO_PORT_REG);
+    while (1) {
+	*p0_port_reg |= (1 << PIN_NUMBER);
+	k_msleep(SLEEP_TIME_MS);
+	*p0_port_reg &= ~(1 << PIN_NUMBER);
+	k_msleep(SLEEP_TIME_MS);
+    }
+    return 0;
+}
+</code>
+Some explanation of the "volatile" qualifier present in the example could help to clear some doubts. In general compilation and run of the above example without "volatile" should work properly. The troubles could start if there is some other part of the code that modifies the same registers. Because of optimization compiler could not read the port state but set it only, which could result in unexpected modification of other outputs. In general volatile qualifier should be used whenever the value of the variable could change unexpectedly. In practice, only three types of variables could change:
+  * Shared global variable modified by an interrupt service routine, used also in the main program
+  * Shared global variable within a multi-threaded application used by more than one thread
+  * Memory-mapped peripheral registers
+In our example, we have that third situation.
 ===== Button example =====
-A similar example named “button” [5] uses one of the onboard buttons to generate interrupts and, at the same time, to control the onboard LED. The button example is not a part of the distribution of the Zephyr package, but can be downloaded from github: https://github.com/zephyrproject-rtos ((https://github.com/zephyrproject-rtos)). Because of this, some paths for including libraries should be adjusted after import (usually it is enough to delete the “zephyr/” from paths marked erroneous).
+A similar example named “button” [5] uses one of the onboard buttons to generate interrupts and, at the same time, to control the onboard LED. The button example is not a part of the distribution of the Zephyr package, but can be downloaded from GitHub: https://github.com/zephyrproject-rtos ((https://github.com/zephyrproject-rtos)). Because of this, some paths for including libraries should be adjusted after import (usually it is enough to delete the “zephyr/” from paths marked erroneous).
 The button is included in the program similar way as LED.
 <code>
@@ Line 176: / Line 214: @@
 ===== Tasks for the laboratory on GPIO =====
   - Import the Blinky (zephyr_blink) example in the VS Code, as shown in the introduction to PlatformIO document.
-  - Find a zephyr-button example. It's not importable as the project, so the simplest solution is to replace files main.c and prj.conf in the already imported project (e.g. Blinky). Files can be found in the folder <code>..\.platformio\packages\framework-zephyr\samples\basic\button\src</code>
+  - Find a zephyr-button example. It's not importable as the project, so the simplest solution is to replace files main.c and prj.conf in the already imported project (e.g. Blinky). Files can be found in the folder <code>..\.platformio\packages\framework-zephyr\samples\basic\button\src</code> The Zephyr-button code is also attached to this instruction at the bottom.
   - Merge two projects “blink”, and “button” together to obtain the program that blinks LED0 continuously, calls the callback function with the interrupt generated with Button0, and controls the state of LED1 with Button1.
+===== The code for the laboratory on GPIO =====
+==== The Zephyr-button code example ====
+<code c>
+/*
+ * Copyright (c) 2016 Open-RnD Sp. z o.o.
+ * Copyright (c) 2020 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <zephyr/kernel.h>
+#include <zephyr/device.h>
+#include <zephyr/drivers/gpio.h>
+#include <zephyr/sys/util.h>
+#include <zephyr/sys/printk.h>
+#include <inttypes.h>
+#define SLEEP_TIME_MS 1
+/*
+ * Get button configuration from the devicetree sw0 alias. This is mandatory.
+ */
+#define SW0_NODE DT_ALIAS(sw0)
+#if !DT_NODE_HAS_STATUS(SW0_NODE, okay)
+#error "Unsupported board: sw0 devicetree alias is not defined"
+#endif
+static const struct gpio_dt_spec button = GPIO_DT_SPEC_GET_OR(SW0_NODE, gpios,
+      {0});
+static struct gpio_callback button_cb_data;
+/*
+ * The led0 devicetree alias is optional. If present, we'll use it
+ * to turn on the LED whenever the button is pressed.
+ */
+static struct gpio_dt_spec led = GPIO_DT_SPEC_GET_OR(DT_ALIAS(led0), gpios,
+     {0});
+void button_pressed(const struct device *dev, struct gpio_callback *cb,
+    uint32_t pins)
+{
+printk("Button pressed at %" PRIu32 "\n", k_cycle_get_32());
+}
+int main(void)
+{
+int ret;
+if (!gpio_is_ready_dt(&button)) {
+printk("Error: button device %s is not ready\n",
+       button.port->name);
+return 0;
+}
+ret = gpio_pin_configure_dt(&button, GPIO_INPUT);
+if (ret != 0) {
+printk("Error %d: failed to configure %s pin %d\n",
+       ret, button.port->name, button.pin);
+return 0;
+}
+ret = gpio_pin_interrupt_configure_dt(&button,
+      GPIO_INT_EDGE_TO_ACTIVE);
+if (ret != 0) {
+printk("Error %d: failed to configure interrupt on %s pin %d\n",
+ret, button.port->name, button.pin);
+return 0;
+}
+gpio_init_callback(&button_cb_data, button_pressed, BIT(button.pin));
+gpio_add_callback(button.port, &button_cb_data);
+printk("Set up button at %s pin %d\n", button.port->name, button.pin);
+if (led.port && !gpio_is_ready_dt(&led)) {
+printk("Error %d: LED device %s is not ready; ignoring it\n",
+       ret, led.port->name);
+led.port = NULL;
+}
+if (led.port) {
+ret = gpio_pin_configure_dt(&led, GPIO_OUTPUT);
+if (ret != 0) {
+printk("Error %d: failed to configure LED device %s pin %d\n",
+       ret, led.port->name, led.pin);
+led.port = NULL;
+} else {
+printk("Set up LED at %s pin %d\n", led.port->name, led.pin);
+}
+}
+printk("Press the button\n");
+if (led.port) {
+while (1) {
+/* If we have an LED, match its state to the button's. */
+int val = gpio_pin_get_dt(&button);
+if (val >= 0) {
+gpio_pin_set_dt(&led, val);
+}
+k_msleep(SLEEP_TIME_MS);
+}
+}
+return 0;
+}
+</code>