hand off the sd card to the samd properly, and remount when it's finished

src/app_console/app_console.cpp

@@ -471,7 +471,7 @@ int CmdSamd(int argc, char** argv) {
   } else if (cmd == "msc") {
     bool current = samd.UsbMassStorage();
     std::cout << "toggling to: " << !current << std::endl;
-    samd.UsbMassStorage(!current);
+    events::System().Dispatch(system_fsm::SamdUsbMscChanged{.en = !current});
   } else if (cmd == "off") {
     std::cout << "bye !!!" << std::endl;
     vTaskDelay(pdMS_TO_TICKS(5));

src/drivers/storage.cpp

@@ -118,8 +118,8 @@ SdStorage::~SdStorage() {
   sdspi_host_remove_device(this->handle_);
   sdspi_host_deinit();
 
-  gpio_.WriteSync(IGpios::Pin::kSdPowerEnable, 0);
   gpio_.WriteSync(IGpios::Pin::kSdMuxDisable, 1);
+  gpio_.WriteSync(IGpios::Pin::kSdPowerEnable, 0);
 }
 
 auto SdStorage::GetFs() -> FATFS* {

src/system_fsm/include/system_events.hpp

@@ -53,6 +53,10 @@ struct SdDetectChanged : tinyfsm::Event {
   bool has_sd_card;
 };
 
+struct SamdUsbMscChanged : tinyfsm::Event {
+  bool en;
+};
+
 struct ChargingStatusChanged : tinyfsm::Event {};
 struct BatteryStateChanged : tinyfsm::Event {
   battery::Battery::BatteryState new_state;

src/system_fsm/include/system_fsm.hpp

@@ -61,6 +61,7 @@ class SystemState : public tinyfsm::Fsm<SystemState> {
   virtual void react(const StorageError&) {}
   virtual void react(const KeyLockChanged&) {}
   virtual void react(const SdDetectChanged&) {}
+  virtual void react(const SamdUsbMscChanged&) {}
   virtual void react(const database::event::UpdateFinished&) {}
   virtual void react(const audio::PlaybackFinished&) {}
   virtual void react(const internal::IdleTimeout&) {}
@@ -101,6 +102,7 @@ class Running : public SystemState {
   void react(const SdDetectChanged&) override;
   void react(const audio::PlaybackFinished&) override;
   void react(const database::event::UpdateFinished&) override;
+  void react(const SamdUsbMscChanged&) override;
 
   using SystemState::react;
 

src/system_fsm/running.cpp

@@ -10,6 +10,7 @@
 #include "db_events.hpp"
 #include "file_gatherer.hpp"
 #include "freertos/projdefs.h"
+#include "gpios.hpp"
 #include "result.hpp"
 
 #include "audio_fsm.hpp"
@@ -55,6 +56,11 @@ void Running::react(const database::event::UpdateFinished&) {
 }
 
 void Running::react(const SdDetectChanged& ev) {
+  if (sServices->samd().UsbMassStorage()) {
+    // We don't currently control the sd card, so don't mess with it.
+    return;
+  }
+
   if (ev.has_sd_card) {
     if (!sStorage && mountStorage()) {
       events::Ui().Dispatch(StorageMounted{});
@@ -64,6 +70,42 @@ void Running::react(const SdDetectChanged& ev) {
   }
 }
 
+void Running::react(const SamdUsbMscChanged& ev) {
+  if (ev.en) {
+    // Stop using the sd card, and power it off.
+    unmountStorage();
+
+    // Set up the SD card for usage by the samd21.
+    auto& gpios = sServices->gpios();
+    gpios.WriteSync(drivers::IGpios::Pin::kSdPowerEnable, 1);
+    gpios.WriteSync(drivers::IGpios::Pin::kSdMuxSwitch,
+                    drivers::IGpios::SD_MUX_SAMD);
+    gpios.WriteSync(drivers::IGpios::Pin::kSdMuxDisable, 0);
+
+    // Off you go!
+    sServices->samd().UsbMassStorage(true);
+  } else {
+    // Make sure the samd knows that its access is going away, and give it time
+    // to finish up any remaining work.
+    sServices->samd().UsbMassStorage(false);
+    vTaskDelay(pdMS_TO_TICKS(250));
+
+    auto& gpios = sServices->gpios();
+    // No more writing, please!
+    gpios.WriteSync(drivers::IGpios::Pin::kSdMuxDisable, 1);
+    vTaskDelay(pdMS_TO_TICKS(100));
+
+    // Reboot the SD card so that it comes up in a consistent state.
+    // TODO: can we avoid doing this?
+    gpios.WriteSync(drivers::IGpios::Pin::kSdPowerEnable, 0);
+
+    // Now it's ready for us.
+    if (mountStorage()) {
+      events::Ui().Dispatch(StorageMounted{});
+    }
+  }
+}
+
 auto Running::mountStorage() -> bool {
   ESP_LOGI(kTag, "mounting sd card");
   auto storage_res = drivers::SdStorage::Create(sServices->gpios());