Add DMA mode to stm32f411/sound_out example.

Author: kraiskil

examples/stm32/f4/stm32f411e-discovery/sound_out/README.md

@@ -10,3 +10,16 @@ Sepeakers attached to the 3.5mm audio jack.
 Note: volume is turned low, but beware of loud sounds
 in case of bugs (i.e. plug the headphones to your ear
 only after playback starts!)
+
+## DMA mode
+
+There is a compile-time option (#define USE_DMA) that
+demonstrates how to have the DMA engine write audio
+data to the DAC.
+
+## LEDs
+
+Both versions of the program blink the orange
+led (PD13) at ~0.5Hz. The DMA version toggles the
+green led (PD12) on every DMA interrupt, which means
+the pattern is visible with oscilloscope only (500Hz).

examples/stm32/f4/stm32f411e-discovery/sound_out/sound_out.c

@@ -1,17 +1,26 @@
 /*
- * Example to show using I2C and I2C with libopencm3.
+ * Example for how to use I2C and I2S with libopencm3.
  * This is intended for the STM32F411-Discovery demoboard.
- * It has a CS42L22 audio DAC onboard.
  *
  * The device plays a 1kHz sine through the audio jack.
  */
 
+/* Compile time option to use DMA to feed audio to the I2S.
+ * Without this, the audio is sent by polling the I2S peripheral's
+ * TXE bit */
+#define USE_DMA
+
 
 #include <libopencm3/stm32/gpio.h>
 #include <libopencm3/stm32/i2c.h>
 #include <libopencm3/stm32/rcc.h>
 #include <libopencm3/stm32/spi.h>
 
+#ifdef USE_DMA
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/stm32/dma.h>
+#endif
+
 
 /* Test audio: 8 points of a sine.
  * At Fs=8kHz, this means a 1kHz audio sine
@@ -36,13 +45,27 @@ static void write_i2c_to_audiochip( uint8_t reg, uint8_t contents)
 	uint8_t packet[2];
 	packet[0] = reg;
 	packet[1] = contents;
-	/* STM32F411 gives device address with R/W bit,
+	/* STM32F411 discovery user's manyal gives device address with R/W bit,
 	 * libopencm wants it without it */
 	uint8_t address = (0x94)>>1;
 
 	i2c_transfer7(I2C1, address, packet, 2, NULL, 0);
 }
 
+#ifdef USE_DMA
+/* Interrupt service routine for the DMA.
+ * The name is "magic" and suffices as installation hook into libopencm3. */
+void dma1_stream5_isr(void)
+{
+	gpio_toggle(GPIOD, GPIO12);
+
+	/* Clear the 'transfer complete' interrupt, or execution would jump right back to this ISR. */
+	if (dma_get_interrupt_flag(DMA1, DMA_STREAM5, DMA_TCIF)) {
+		dma_clear_interrupt_flags(DMA1, DMA_STREAM5, DMA_TCIF);
+	}
+}
+#endif
+
 int main(void)
 {
 	/* Set device clocks from opencm3 provided preset.*/
@@ -54,8 +77,12 @@ int main(void)
 	rcc_periph_clock_enable(RCC_GPIOC);
 	rcc_periph_clock_enable(RCC_GPIOD);
 
-	/* Initialize "heartbeat" LED GPIO */
-	gpio_mode_setup(GPIOD, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO13);
+	/* Initialize "heartbeat" LED GPIOs. */
+#ifdef USE_DMA
+	gpio_mode_setup(GPIOD, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO12); /* green led */
+#endif
+	gpio_mode_setup(GPIOD, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO13); /* orange led */
+
 
 	/* I2C GPIO pins
 	 * PB6 - SCL (I2C clock)
@@ -73,6 +100,7 @@ int main(void)
 	gpio_set_af(GPIOB, GPIO_AF4, GPIO6);
 	gpio_set_af(GPIOB, GPIO_AF4, GPIO9);
 
+
 	/* Initialize the I2C itself.
 	 * Since we are master, we would not need to initialize slave
 	 * address, but this is the only libopencm3 API call that sets
@@ -84,6 +112,7 @@ int main(void)
 	i2c_set_own_7bit_slave_address(I2C1, 0);
 	i2c_peripheral_enable(I2C1);
 
+
 	/* Initialize I2S.
 	 * I2S is implemented as a HW mode of the SPI peripheral.
 	 * Since this is a STM32F411, there is a separate I2S PLL
@@ -96,8 +125,7 @@ int main(void)
 	i2s_set_dataformat(SPI3, i2s_dataframe_ch16_data16);
 	i2s_set_mode(SPI3, i2s_mode_master_transmit);
 	i2s_masterclock_enable(SPI3);
-	/* RCC_PLLI2SCFGR configured values are:
-	 * 0x24003010 i.e.
+	/* RCC_PLLI2SCFGR is left at reset value: 0x24003010 i.e.
 	 * PLLR = 2
 	 * PLLI2SN = 192
 	 * PLLI2SM = 16
@@ -107,9 +135,14 @@ int main(void)
 	 * STM32F411 reference manual:
 	 * Fs = I2Sclk/ (32*2 * ((2*I2SDIV)+ODD)*4)
 	 * I2SDIV = I2Sclk/(512*Fs)
-	 * I2SDIV=24 => 23,4 so 23 + ODD bit set
+	 * Fs=8kHz => I2SDIV=23,4 so 23 + ODD bit set
 	 */
 	i2s_set_clockdiv(SPI3, 23, 1);
+#ifdef USE_DMA
+	/* Have the SPI/I2S peripheral ping the DMA each time data is sent.
+	 * The DMA peripheral is configured later. */
+	spi_enable_tx_dma(SPI3);
+#endif
 	i2s_enable(SPI3);
 
 
@@ -138,16 +171,47 @@ int main(void)
 	write_i2c_to_audiochip(0x02, 0x9e); // power control 1: Magic value to power up the chip
 
 
+#ifdef USE_DMA
+	/* Enable DMA from memory to I2S peripheral.
+	 * The DMA is configured as circular, i.e. it restarts automatically when
+	 * the requested amount of datasamples are set.
+	 * SPI3/I2S3 is available on DMA1 stream 5, channel 0 (see RM 0383, table 27) */
+	rcc_periph_clock_enable(RCC_DMA1);
+	nvic_enable_irq(NVIC_DMA1_STREAM5_IRQ);
+	dma_disable_stream(DMA1, DMA_STREAM5);
+	dma_set_priority(DMA1, DMA_STREAM5, DMA_SxCR_PL_HIGH);
+	dma_set_memory_size(DMA1, DMA_STREAM5, DMA_SxCR_MSIZE_16BIT);
+	dma_set_peripheral_size(DMA1, DMA_STREAM5, DMA_SxCR_PSIZE_16BIT);
+	dma_enable_memory_increment_mode(DMA1, DMA_STREAM5);
+	dma_enable_circular_mode(DMA1, DMA_STREAM5);
+	dma_set_transfer_mode(DMA1, DMA_STREAM5, DMA_SxCR_DIR_MEM_TO_PERIPHERAL);
+	dma_set_peripheral_address(DMA1, DMA_STREAM5, (uint32_t) &SPI_DR(SPI3));
+	dma_set_memory_address(DMA1, DMA_STREAM5, (uint32_t) audio);
+	dma_set_number_of_data(DMA1, DMA_STREAM5, sizeof(audio)/sizeof(audio[0]));
+	dma_enable_transfer_complete_interrupt(DMA1, DMA_STREAM5);
+	dma_channel_select(DMA1, DMA_STREAM5, DMA_SxCR_CHSEL_0);
+	dma_enable_stream(DMA1, DMA_STREAM5);
+#endif
+
+
 	while(1) {
-		/* Blink the heartbeat LED */
-		static int blinkslowdown=0;
-		if( ++blinkslowdown == 8000) {
+		/* Blink the heartbeat LED at ~0,5Hz*/
+#ifdef USE_DMA
+		const int blinkslowdown = 20e6;
+#else
+		const int blinkslowdown = 1000;
+#endif
+		static int i=0;
+		if( ++i > blinkslowdown) {
 			gpio_toggle(GPIOD, GPIO13);
-			blinkslowdown=0;
+			i=0;
 		}
 
-		for( unsigned i=0; i < sizeof(audio)/sizeof(audio[0]); i++)
-			spi_send(SPI3, audio[i]);
+#ifndef USE_DMA
+		/* Blocking send of the data buffer */
+		for( unsigned j=0; j < sizeof(audio)/sizeof(audio[0]); j++)
+			spi_send(SPI3, audio[j]);
+#endif
 	}
 	return 0;
 }