Additional multicore fixes, BOOTSEL and PIO (#123)

BOOTSEL needs to be multicore protected, too.
Reading BOOTSEL required disabling the flash interface, so the other
core needs to be idles while this runs.

Make the PIO program object multicore safe, too, so that if both cores
try to load a program they won't step on each other.

cores/rp2040/Bootsel.cpp

@@ -26,7 +26,8 @@ static bool __no_inline_not_in_flash_func(get_bootsel_button)() {
 
     // Must disable interrupts, as interrupt handlers may be in flash, and we
     // are about to temporarily disable flash access!
-    uint32_t flags = save_and_disable_interrupts();
+    noInterrupts();
+    rp2040.idleOtherCore();
 
     // Set chip select to Hi-Z
     hw_write_masked(&ioqspi_hw->io[CS_PIN_INDEX].ctrl,
@@ -46,7 +47,8 @@ static bool __no_inline_not_in_flash_func(get_bootsel_button)() {
                     GPIO_OVERRIDE_NORMAL << IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB,
                     IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS);
 
-    restore_interrupts(flags);
+    interrupts();
+    rp2040.resumeOtherCore();
 
     return button_state;
 }

cores/rp2040/RP2040.h

@@ -23,6 +23,7 @@
 #include <hardware/pio.h>
 #include <pico/multicore.h>
 #include <pico/util/queue.h>
+#include <CoreMutex.h>
 
 class _MFIFO {
 public:
@@ -132,7 +133,6 @@ public:
 extern RP2040 rp2040;
 
 // Wrapper class for PIO programs, abstracting common operations out
-// TODO - Make dualcore safe
 // TODO - Add unload/destructor
 class PIOProgram {
 public:
@@ -140,6 +140,8 @@ public:
 
     // Possibly load into a PIO and allocate a SM
     bool prepare(PIO *pio, int *sm, int *offset) {
+        extern mutex_t _pioMutex;
+        CoreMutex m(&_pioMutex);
         // Is there an open slot to run in, first?
         if (!_findFreeSM(pio, sm)) return false;
 	// Is it loaded on that PIO?

cores/rp2040/main.cpp

@@ -26,6 +26,9 @@ RP2040 rp2040;
 
 volatile bool _MFIFO::_otherIdled = false;
 
+auto_init_mutex(_pioMutex);
+
+
 extern void setup();
 extern void loop();