raspberrypi: Make port_idle_until_interrupt work

This needs thorough testing before it's merged, as we tried
and reverted this once before (adafruit#5341 and adafruit#5356).

I think that besides checking for tinyusb having "something to do",
the fact that `port_interrupt_after_ticks` and `port_disable_tick`
weren't implemented that was causing a secondary problem.

I've tested this on a pico w over reboot-cycles and ctrl-c-cycles,
with and without drive automounting, with and without serial repl open,
and on a power-only connection.

I didn't notice the problem reported in adafruit#5356 after merely implementing
port_idle_until_interrupt; but I did notice that sleeps in general would
take over-long until "something" (like writing to the USB drive) happened;
I think "something" was probably calling port_enable_tick(). When this
problem was happening, sleeps would take a lot longer; for instance,
`sleep(.001)` would take about 1/20s and `sleep(.1)` would take about 1/7s.

ports/raspberrypi/Makefile

@@ -127,6 +127,7 @@ INC += \
         -I../shared/timeutils \
         -Iboards/$(BOARD) \
         -Iboards/ \
+        -isystem ./../../lib/cmsis/inc \
         -isystem sdk/ \
         -isystem sdk/src/common/pico_base/include/ \
         -isystem sdk/src/common/pico_binary_info/include/ \

ports/raspberrypi/supervisor/port.c

@@ -72,6 +72,9 @@
 
 #include "supervisor/serial.h"
 
+#include "tusb.h"
+#include <cmsis_compiler.h>
+
 extern volatile bool mp_msc_enabled;
 
 STATIC void _tick_callback(uint alarm_num);
@@ -241,38 +244,48 @@ uint32_t port_get_saved_word(void) {
     return __scratch_x_start__;
 }
 
+static volatile bool ticks_enabled;
+
 uint64_t port_get_raw_ticks(uint8_t *subticks) {
     uint64_t microseconds = time_us_64();
     return 1024 * (microseconds / 1000000) + (microseconds % 1000000) / 977;
 }
 
 STATIC void _tick_callback(uint alarm_num) {
-    supervisor_tick();
-    hardware_alarm_set_target(0, delayed_by_us(get_absolute_time(), 977));
+    if (ticks_enabled) {
+        supervisor_tick();
+        hardware_alarm_set_target(0, delayed_by_us(get_absolute_time(), 977));
+    }
 }
 
 // Enable 1/1024 second tick.
 void port_enable_tick(void) {
+    ticks_enabled = true;
     hardware_alarm_set_target(0, delayed_by_us(get_absolute_time(), 977));
 }
 
 // Disable 1/1024 second tick.
 void port_disable_tick(void) {
-    // hardware_alarm_cancel(0);
+    // One additional _tick_callback may occur, but it will just return
+    // whenever !ticks_enabled. Cancel is not called just in case
+    // it could nuke a timeout set by port_interrupt_after_ticks.
+    ticks_enabled = false;
 }
 
 // This is called by sleep, we ignore it when our ticks are enabled because
 // they'll wake us up earlier. If we don't, we'll mess up ticks by overwriting
 // the next RTC wake up time.
 void port_interrupt_after_ticks(uint32_t ticks) {
+    if (!ticks_enabled) {
+        hardware_alarm_set_target(0, delayed_by_us(get_absolute_time(), ticks * 977));
+    }
 }
 
 void port_idle_until_interrupt(void) {
     common_hal_mcu_disable_interrupts();
-    if (!background_callback_pending()) {
-        // TODO: Does not work when board is power-cycled.
-        // asm volatile ("dsb 0xF" ::: "memory");
-        // __wfi();
+    if (!background_callback_pending() && !tud_task_event_ready()) {
+        __DSB();
+        __WFI();
     }
     common_hal_mcu_enable_interrupts();
 }