tweak timeout for resume

Signed-off-by: Taylor Yu <[email protected]>

src/kaleidoscope/driver/hid/tinyusb/HIDD.h

@@ -47,18 +47,35 @@ class HIDD : public Adafruit_USBD_HID {
   bool sendReport(uint8_t report_id, void const *report, uint8_t len) {
     if (TinyUSBDevice.suspended()) {
       TinyUSBDevice.remoteWakeup();
-      /* Block (with timeout) to avoid dropping events on resume */
-      for (int timeout = 250; timeout--;) {
-        if (ready()) {
-          break;
-        }
-        delay(1);
-      }
+      /*
+       * Wait for 30ms, which is the minimum required by spec for a resume.
+       * (USB 2.0 §7.1.7.7)
+       *
+       * 20ms of host echoing the resume downstream, and 10ms of recovery time
+       * once the bus has resumed.
+       */
+      delay(30);
     }
     /*
-     * Might need an additional timeout here, in case bus is resumed but host
-     * isn't polling, and the FIFO or peripheral is full
+     * Block for up to 250ms for endpoint to become ready. If the host is polling,
+     * this should take about 1ms (the requested polling interval, but the
+     * host is allowed to poll less frequently). On resume, especially remote
+     * wakeup on macOS, not only can the resume take longer much than the
+     * minimum (over 2 seconds, instead of 20ms), the recovery period can be
+     * over 100ms (instead of 10ms).
+     *
+     * This will mitigate, but not necessarily eliminate, stuck key situations
+     * during resume. One scenario is a key down report being queued while in
+     * the recovery period, where the bus has resumed, but the host isn't
+     * polling yet. The endpoint will be ready, but the transmission won't
+     * happen until the host resumes polling. The transmission of the key up
+     * event might time out, leading to a stuck key situation.
+     *
+     * Unfortunately, we usually can't abort a packet transmission once queued.
      */
+    for (int timeout = 250; timeout-- && !ready();) {
+      delay(1);
+    }
     if (!ready()) {
       return false;
     }