samples: hid-keyboard: use sample to measure SOF event latency

The keyboard sample is quite simple and there is not much happening
outside of the USB controller activity, use it to measure the latency
since the SOF interrupt. This approach only works with UDC drivers that
update the frame number on the SOF interrupt.

Signed-off-by: Johann Fischer <[email protected]>

Author: jfischer-no

samples/subsys/usb/hid-keyboard/prj.conf

@@ -6,7 +6,7 @@ CONFIG_USBD_LOG_LEVEL_WRN=y
 CONFIG_USBD_HID_LOG_LEVEL_WRN=y
 CONFIG_UDC_DRIVER_LOG_LEVEL_WRN=y
 CONFIG_SAMPLE_USBD_PID=0x0007
-CONFIG_SAMPLE_USBD_REMOTE_WAKEUP=y
+CONFIG_SAMPLE_USBD_REMOTE_WAKEUP=n
 
 CONFIG_GPIO=y
 CONFIG_INPUT=y

samples/subsys/usb/hid-keyboard/src/main.c

@@ -12,11 +12,16 @@
 #include <zephyr/input/input.h>
 
 #include <zephyr/usb/usbd.h>
+#include <zephyr/drivers/usb/udc.h>
 #include <zephyr/usb/class/usbd_hid.h>
 
 #include <zephyr/logging/log.h>
 LOG_MODULE_REGISTER(main, LOG_LEVEL_INF);
 
+#if CONFIG_UDC_ENABLE_SOF
+static const struct device *const udc_dev = DEVICE_DT_GET(DT_NODELABEL(zephyr_udc0));
+#endif
+
 static const uint8_t hid_report_desc[] = HID_KEYBOARD_REPORT_DESC();
 
 enum kb_leds_idx {
@@ -133,6 +138,27 @@ static void kb_output_report(const struct device *dev, const uint16_t len,
 	kb_set_report(dev, HID_REPORT_TYPE_OUTPUT, 0U, len, buf);
 }
 
+#if CONFIG_UDC_ENABLE_SOF
+/*
+ * Use it to measure the latency since the SOF interrupt. Do not blindly trust
+ * the value unless it has been verified with e.g. an osciloscope. The value is
+ * the best case, because in this sample not much happens outside the USB
+ * controller activity. It only works with UDC drivers that update the frame
+ * number on the SOF interrupt.
+ */
+static void kb_sof(const struct device *dev)
+{
+	uint16_t fnumber = udc_get_frame_number(udc_dev);
+	uint64_t stamp = udc_get_sof_stamp(udc_dev);
+
+	(void)gpio_pin_toggle_dt(&kb_leds[0]);
+	if (fnumber == 1366) {
+		LOG_INF("Time since SOF ISR %llu us",
+			k_cyc_to_us_ceil64(k_cycle_get_64() - stamp));
+	}
+}
+#endif
+
 struct hid_device_ops kb_ops = {
 	.iface_ready = kb_iface_ready,
 	.get_report = kb_get_report,
@@ -141,6 +167,7 @@ struct hid_device_ops kb_ops = {
 	.get_idle = kb_get_idle,
 	.set_protocol = kb_set_protocol,
 	.output_report = kb_output_report,
+	IF_ENABLED(CONFIG_UDC_ENABLE_SOF, (.sof = kb_sof,))
 };
 
 /* doc device msg-cb start */