implement SPI clean exit

src/dmdreader.cpp

@@ -240,6 +240,23 @@ void start_spi() { digitalWrite(SPI0_CS, HIGH); }
  */
 void finish_spi() { digitalWrite(SPI0_CS, LOW); }
 
+/**
+ * @brief Cleanly exit SPI by stopping the DMD pio and sending a blank dummy
+ * frame.
+ *
+ */
+void spi_clean_exit() {
+  static bool exit_executed = false;
+  if (spi_busy() || exit_executed) {
+    return;
+  }
+
+  pio_sm_set_enabled(dmd_pio, dmd_sm, false);
+  memset(framebuf1, 0, target_bytes);
+  memset(framebuf2, 0, target_bytes);
+  frame_received = exit_executed = true;
+}
+
 /**
  * @brief Send a pix buffer via SPI
  *
@@ -1544,12 +1561,14 @@ void dmdreader_spi_init() {
   irq_set_enabled(DMA_IRQ_1, true);
 }
 
-bool dmdreader_spi_send() {
+bool dmdreader_spi_send(bool is_restarting) {
   if (!loopback && frame_received) {
     frame_received = false;
     spi_send_pix(framebuf_to_send, frame_crc, true);
 
     return true;
+  } else if (is_restarting) {
+    spi_clean_exit();
   }
 
   return false;

src/dmdreader.h

@@ -46,7 +46,7 @@ enum DmdType : uint8_t {
 bool dmdreader_init(bool return_on_no_detection = false);
 
 void dmdreader_spi_init();
-bool dmdreader_spi_send();
+bool dmdreader_spi_send(bool is_restarting = false);
 
 void dmdreader_loopback_init(uint8_t *buffer1, uint8_t *buffer2, Color color);
 void dmdreader_loopback_stop();