Timestamp:

04/12/2022 09:13:18 PM (2 years ago)

Author:

Tim Harvey

Comment:

updated code example for a Linux Input Event

gsc

@@ -671 +671 @@
   * please see [#IRQ_GPIO_CHANGE here] regarding un-terminated inputs causing spurious GPIO_CHANGE events
 
-The gpio-keys kernel driver will produce Linux Input events for the above interrupts.
+The gpio-keys kernel driver will produce Linux Input events for the above interrupts. This is configured in the board device-tree and maps the pushbutton GPIO to a BTN_0 event such that when the button is down the value will be 1 and up will be 0.
+
 
 In addition, the user pushbutton state is available on a GPIO in case you need to do anything more flexible than the above built-in interrupt functionality:
@@ -709 +710 @@
 
 
-=== Code Examples for software user pushbutton detection ===
-The following example will configure the GSC for SW pushbutton interrupt and read the PB state by polling the GPIO (see above):
-{{{
-#!bash
-# clear R0.1 bit to disable pushbutton hard reset - taking care to not disturb other bits
-R0=$(i2cget -f -y 0 0x20 0) && \
-  R0=$((R0 & ~0x01)) && \
-  i2cset -f -y 0 0x20 0 $R0 || echo i2c error
-# export gpio240 to userspace (Note this value is board specific - see above table)
-# If using mainline BSP with different GPIO ranges "cat /sys/kernel/gpio" look for pca9555 emulated over i2c, if Ventana use lowest number in range, if Newport use lowest number in range + 2
-echo 240 > /sys/class/gpio/export
-while [ 1 ]; do
-  cat /sys/class/gpio/gpio240/value ;# PB state 0 or 1
-done
-}}}
-
-A more appropriate method of detection may be to use the fact that the GSC has interrupt support and use the libc {{{poll(2)}}} function to block on the GPIO until it changes state. See [wiki:gpio#catchingagpiochangefromuserspacewithoutpolling Catching a GPIO from Userspace w/o polling] for an example of how to do that.
+=== Code Example for software user pushbutton detection ===
+The following code example shows how to watch for a Linux Input event of BTN_0 for the gpio-keys driver:
+{{{
+#include <fcntl.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#include <linux/input.h>
+
+int main(int argc, char *argv[])
+{
+        const char *dev = "/dev/input/by-path/platform-gpio-keys-event";
+        int report_sec = 5; /* seconds between report held activity */
+        struct input_event ie, last_ie; /* input event tracking */
+        int timeout_sec = 1; /* poll period */
+        int report = 0; /* last report time */
+        int count = 0; /* successive click counter */
+        struct pollfd fdset;
+        int fd;
+
+        /* open input device for gpio-keys */
+        if ((fd = open(dev, O_RDONLY)) == -1) {
+                perror("opening device");
+                exit(EXIT_FAILURE);
+        }
+
+        last_ie.time.tv_sec = time(NULL);
+        report = time(NULL);
+        while (1) {
+                /* use poll to block for timeout_sec seconds */
+                fdset.fd = fd;
+                fdset.events = POLLIN;
+                fdset.revents = 0;
+                if (poll(&fdset, 1, timeout_sec * 1000) == -1) {
+                        perror("poll");
+                        exit(EXIT_FAILURE);
+                }
+
+                /* if we have a button event - capture it */
+                if (fdset.revents == POLLIN) {
+                        read(fd, &ie, sizeof(struct input_event));
+                        if (ie.type == EV_KEY && ie.code == BTN_0) {
+                                memcpy(&last_ie, &ie, sizeof(ie));
+                                report = 0;
+                                /* increment click count on up */
+                                if (!ie.value)
+                                        count++;
+                        }
+                }
+
+                /* if no state change in more than 1s reset click count */
+                if ((time(NULL) - last_ie.time.tv_sec) > 1) {
+                        count = 0;
+                        report = 0;
+                }
+
+                /* if time to report */
+                if ((time(NULL) - report) >= report_sec) {
+                        fprintf(stderr,
+                                "%d: %s for %d secs\n", count,
+                                last_ie.value ? "down" : "up",
+                                (int) (time(NULL) - last_ie.time.tv_sec));
+                        report = time(NULL);
+                }
+        }
+
+        close(fd);
+
+        return EXIT_SUCCESS;
+}
+
+}}}
+ * poll() is used with a timeout of 1s to simplify the tracking of time
+ * we are only interested above in BTN_0 events from {{{/dev/input/by-path/platform-gpio-keys-event}}} which coorespond to a change in user pushbutton
+ * you most likely want to clear R0.1 to disable hard reset on a 1x quick-press-and-release if using the above
+ * we increment a click counter if the button state change occured within 1 second of the last
+ * each time a button up/down event occurs the current click count and state will be displayed
+ * when button state has not changed in 5 seconds (report_sec) the a message will show the current button state and seconds it has been in that state; this could be used to mean 'held (up or down) for <report_sec>' time if you want to catch a hold event
 
 See also: