AudioPlaySdWav: buffer alignment and irq priority

Audio.h

@@ -55,6 +55,37 @@
 #define AudioNoInterrupts() (NVIC_DISABLE_IRQ(IRQ_SOFTWARE))
 #define AudioInterrupts()   (NVIC_ENABLE_IRQ(IRQ_SOFTWARE))
 
+/**
+  \brief Get Base Priority
+  \details Returns the current value of the Base Priority register
+  \return Base Priority register value
+ */
+static inline uint32_t __get_BASEPRI() __attribute__((always_inline));
+
+static inline uint32_t __get_BASEPRI() {
+	uint32_t result;
+	__asm volatile(
+		"mrs %0, basepri"
+		: "=r" (result)
+	);
+	return result;
+}
+
+
+/**
+  \brief Set Base Priority
+  \details Assigns the given value to the Base Priority register
+  \param[in] basePri Base Priority value to set
+ */
+static inline void __set_BASEPRI(const uint32_t value) __attribute__((always_inline));
+
+static inline void __set_BASEPRI(const uint32_t value) {
+	__asm volatile(
+		"msr basepri, %0"
+		:: "r" (value) : "memory"
+	);
+}
+
 // include all the library headers, so a sketch can use a single
 // #include <Audio.h> to get the whole library
 //

play_sd_raw.cpp

@@ -25,6 +25,7 @@
  */
 
 #include <Arduino.h>
+#include "Audio.h"
 #include "play_sd_raw.h"
 #include "spi_interrupt.h"
 
@@ -45,9 +46,12 @@ bool AudioPlaySdRaw::play(const char *filename)
 #else
 	AudioStartUsingSPI();
 #endif
-	__disable_irq();
+	/* disable interrupts with lower priority than SDHC DMA */
+	const uint32_t last_pri { __get_BASEPRI() };
+	const uint8_t sdhc_pri { NVIC_GET_PRIORITY(IRQ_SDHC) };
+	__set_BASEPRI((sdhc_pri / 16U + 1U) * 16U);
 	rawfile = SD.open(filename);
-	__enable_irq();
+	__set_BASEPRI(last_pri);
 	if (!rawfile) {
 		//Serial.println("unable to open file");
 		#if defined(HAS_KINETIS_SDHC)

play_sd_wav.cpp

@@ -25,6 +25,7 @@
  */
 
 #include <Arduino.h>
+#include "Audio.h"
 #include "play_sd_wav.h"
 #include "spi_interrupt.h"
 
@@ -67,9 +68,12 @@ bool AudioPlaySdWav::play(const char *filename)
 #else 	
 	AudioStartUsingSPI();
 #endif
-	__disable_irq();
+	/* disable interrupts with lower priority than SDHC DMA */
+	const uint32_t last_pri { __get_BASEPRI() };
+	const uint8_t sdhc_pri { NVIC_GET_PRIORITY(IRQ_SDHC) };
+	__set_BASEPRI((sdhc_pri / 16U + 1U) * 16U);
 	wavfile = SD.open(filename);
-	__enable_irq();
+	__set_BASEPRI(last_pri);
 	if (!wavfile) {
 	#if defined(HAS_KINETIS_SDHC)	
 		if (!(SIM_SCGC3 & SIM_SCGC3_SDHC)) AudioStopUsingSPI();

play_sd_wav.h

@@ -53,7 +53,7 @@ class AudioPlaySdWav : public AudioStream
 	audio_block_t *block_left;
 	audio_block_t *block_right;
 	uint16_t block_offset;		// how much data is in block_left & block_right
-	uint8_t buffer[512];		// buffer one block of data
+	alignas(4) uint8_t buffer[512]; // buffer one block of data
 	uint16_t buffer_offset;		// where we're at consuming "buffer"
 	uint16_t buffer_length;		// how much data is in "buffer" (512 until last read)
 	uint8_t header_offset;		// number of bytes in header[]