+static u16_t seq = 0;
+
+static void button_pressed() {
+ /* TODO: This is interrupt context. We need to get out of interrupt context
+ * quickly; we should not be doing significant work here, & definitely
+ * shouldn't be sleeping here. We signal errors with blinking the LED, which
+ * involves sleeping, so this all has to move. */
+ send_report(seq++, 0);
+ signal(4, 200);
+}
+
+static void wait_forever() {
+ /* pico-examples/gpio/hello_gpio_irq/hello_gpio_irq.c implements wait-forever
+ * as "while (1);", but
+ * https://www.raspberrypi.com/documentation/pico-sdk/high_level.html#gaf469c6d691230e9d1008
+ * says sleeping uses less power, so we sleep. */
+ while (1) {
+ /* https://www.raspberrypi.com/documentation/pico-sdk/hardware.html#rpip7ce2cdc1662dce59296b
+ * says the maximum sleep is 2^32 - 1 microseconds (~71.58 minutes), so we
+ * sleep in chunks. */
+ sleep_ms(1 << 31); /* 35.79 minutes */
+ }
+}