bug #376: disable the "wake on serial" feature, because it causes

bogus wakes on TBEAMS because the USB->SERIAL chip pulls the RX input
to ground.  This feature is no longer needed because in !isRouter
nodes we force the node to never sleep anyways when on USB power.

    // this doesn't work on TBEAMs when the USB is depowered (causes bogus interrupts)
    // So we disable this "wake on serial" feature - because now when a TBEAM (only) has power connected it
    // never tries to go to sleep if the user is using the API
    // gpio_wakeup_enable((gpio_num_t)SERIAL0_RX_GPIO, GPIO_INTR_LOW_LEVEL);

docs/software/gps-todo.txt

@@ -8,8 +8,6 @@ time only mode
 
 record power measurements and update spreadsheet
 
-fix uart wake from sleep 
-
 fix has_gps based on new logic
 
 don't send locations if the user has forbidden that (lie to phone so phone won't either)

src/sleep.cpp

@@ -261,12 +261,20 @@ esp_sleep_wakeup_cause_t doLightSleep(uint64_t sleepMsec) // FIXME, use a more r
     // We treat the serial port as a GPIO for a fast/low power way of waking, if we see a rising edge that means
     // someone started to send something
 
-    // Alas - doesn't work reliably, instead need to use the uart specific version (which burns a little power)
-    // FIXME: gpio 3 is RXD for serialport 0 on ESP32
+    // gpio 3 is RXD for serialport 0 on ESP32
     // Send a few Z characters to wake the port
-    gpio_wakeup_enable((gpio_num_t)SERIAL0_RX_GPIO, GPIO_INTR_LOW_LEVEL);
-    // uart_set_wakeup_threshold(UART_NUM_0, 3);
-    // esp_sleep_enable_uart_wakeup(0);
+
+    // this doesn't work on TBEAMs when the USB is depowered (causes bogus interrupts)
+    // So we disable this "wake on serial" feature - because now when a TBEAM (only) has power connected it
+    // never tries to go to sleep if the user is using the API
+    // gpio_wakeup_enable((gpio_num_t)SERIAL0_RX_GPIO, GPIO_INTR_LOW_LEVEL);
+
+    // doesn't help - I think the USB-UART chip losing power is pulling the signal llow
+    // gpio_pullup_en((gpio_num_t)SERIAL0_RX_GPIO);
+
+    // alas - can only work if using the refclock, which is limited to about 9600 bps
+    // assert(uart_set_wakeup_threshold(UART_NUM_0, 3) == ESP_OK);
+    // assert(esp_sleep_enable_uart_wakeup(0) == ESP_OK);
 #endif
 #ifdef BUTTON_PIN
     gpio_wakeup_enable((gpio_num_t)BUTTON_PIN, GPIO_INTR_LOW_LEVEL); // when user presses, this button goes low