PWM audio now works using either CPU or DMA in part9-sound demo

part9-sound/README.md

@@ -10,5 +10,5 @@ This code was derived from [Peter Lemon's work](https://github.com/PeterLemon/Ra
 Todo
 ----
  * Write-up the CPU-driven `playaudio_cpu()` code, explaining clocks/PWM etc.
- * Code the DMA version so we don't have to tie up the CPU
+ * Write-up the DMA version `playaudio_dma()` version, which doesn't tie up the CPU but still plays sound!
  * Add a Makefile.gcc (I'm using LLVM Clang these days, so not a priority)

part9-sound/io.h

@@ -1,4 +1,6 @@
 #define PERIPHERAL_BASE 0xFE000000
+#define LEGACY_BASE     0x7E000000
+#define SAFE_ADDRESS    0x00400000 // Somewhere safe to store a lot of data
 
 void uart_init();
 void uart_writeText(char *buffer);

part9-sound/kernel.c

@@ -2,13 +2,18 @@
 #include "io.h"
 
 #define PWM_BASE        (PERIPHERAL_BASE + 0x20C000 + 0x800) /* PWM1 register base address on RPi4 */
+#define PWM_LEGACY_BASE     (LEGACY_BASE + 0x20C000 + 0x800) /* PWM1 register base legacy address on RPi4 */
 #define CLOCK_BASE      (PERIPHERAL_BASE + 0x101000)
+#define DMA_BASE        (PERIPHERAL_BASE + 0x007100)         /* DMA register base address */
+#define DMA_ENABLE      (DMA_BASE + 0xFF0)                   /* DMA global enable bits */
 
 #define BCM2711_PWMCLK_CNTL 40
 #define BCM2711_PWMCLK_DIV  41
+#define PM_PASSWORD 0x5A000000 
 
 #define BCM2711_PWM_CONTROL 0
 #define BCM2711_PWM_STATUS  1
+#define BCM2711_PWM_DMAC    2
 #define BCM2711_PWM0_RANGE  4
 #define BCM2711_PWM0_DATA   5
 #define BCM2711_PWM_FIFO    6
@@ -17,41 +22,99 @@
 
 #define BCM2711_PWM1_USEFIFO  0x2000  /* Data from FIFO */
 #define BCM2711_PWM1_ENABLE   0x0100  /* Channel enable */
-
 #define BCM2711_PWM0_USEFIFO  0x0020  /* Data from FIFO */
 #define BCM2711_PWM0_ENABLE   0x0001  /* Channel enable */
+#define BCM2711_PWM_ENAB      0x80000000  /* PWM DMA Configuration: DMA Enable (bit 31 set) */
 
 #define BCM2711_GAPO2 0x20
 #define BCM2711_GAPO1 0x10
 #define BCM2711_RERR1 0x8
 #define BCM2711_WERR1 0x4
 #define BCM2711_FULL1 0x1
-
-#define PM_PASSWORD 0x5A000000 
-
 #define ERRORMASK (BCM2711_GAPO2 | BCM2711_GAPO1 | BCM2711_RERR1 | BCM2711_WERR1)
 
+#define DMA_CS        0       /* Control/status register offset for DMA channel 0 */
+#define DMA_CONBLK_AD 1
+#define DMA_EN1       1 << 1  /* Enable DMA engine 1 */
+#define DMA_ACTIVE    1       /* Active bit set */
+#define DMA_DEST_DREQ 0x40    /* Use DREQ to pace peripheral writes */
+#define DMA_PERMAP_1  0x10000 /* PWM1 peripheral for DREQ */
+#define DMA_SRC_INC   0x100   /* Increment source address */
+
 volatile unsigned* clk = (void*)CLOCK_BASE;
 volatile unsigned* pwm = (void*)PWM_BASE;
+volatile unsigned* dma = (void*)DMA_BASE;
+volatile unsigned* dmae = (void*)DMA_ENABLE;
+volatile unsigned* safe = (void*)SAFE_ADDRESS;
+
+struct dma_cb {
+   unsigned int ti;
+   unsigned int source_ad;
+   unsigned int dest_ad;
+   unsigned int txfr_len;
+   unsigned int stride;
+   unsigned int nextconbk;
+   unsigned int null1;
+   unsigned int null2;
+} __attribute__((aligned(32)));
+
+struct dma_cb playback_cb;
+
+static void playaudio_dma(void)
+{
+    extern unsigned char _binary_audio_bin_start[];
+    extern unsigned char _binary_audio_bin_size[];
+    
+    unsigned int size = (long)&_binary_audio_bin_size;
+    unsigned char *data = &(_binary_audio_bin_start[0]);
+
+    // Convert data
+    for (int i=0;i<size;i++) *(safe+i) = *(data+i);
+
+    wait_msec(2);
+
+    // Set up control block
+    playback_cb.ti = DMA_DEST_DREQ + DMA_PERMAP_1 + DMA_SRC_INC;
+    playback_cb.source_ad = SAFE_ADDRESS;
+    playback_cb.dest_ad = PWM_LEGACY_BASE + 0x18; // Should be PWM_FIFO but it's an absolute offset so...
+    playback_cb.txfr_len = size * 4; // They're unsigned ints now, not unsigned chars
+    playback_cb.stride = 0x00;
+    playback_cb.nextconbk = 0x00;
+    playback_cb.null1 = 0x00;
+    playback_cb.null2 = 0x00;
+
+    wait_msec(2);
+
+    // Enable DMA
+    *(pwm+BCM2711_PWM_DMAC) = 
+          BCM2711_PWM_ENAB + 0x0707; // Bits 0-7 Threshold For DREQ Signal = 1, Bits 8-15 Threshold For PANIC Signal = 0
+    *dmae = DMA_EN1;
+    *(dma+DMA_CONBLK_AD) = (long)&playback_cb; // checked and correct
+
+    wait_msec(2);
+
+    *(dma+DMA_CS) = DMA_ACTIVE;
+}
 
 static void audio_init(void)
 {   
     gpio_useAsAlt0(40); // Ensure PWM1 is mapped to GPIO 40/41
     gpio_useAsAlt0(41);
-
     wait_msec(2);
 
+    // Setup clock
+    
     *(clk + BCM2711_PWMCLK_CNTL) = PM_PASSWORD | (1 << 5); // Stop clock
+    wait_msec(2);
 
     int idiv = 2;
     *(clk + BCM2711_PWMCLK_DIV)  = PM_PASSWORD | (idiv<<12);
-    *(clk + BCM2711_PWMCLK_CNTL) = PM_PASSWORD | 16 | 1; // Enable + oscillator
+    *(clk + BCM2711_PWMCLK_CNTL) = PM_PASSWORD | 16 | 1;  // osc + enable
-
     wait_msec(2);
 
-    // Disable PWM
+    // Setup PWM
-    *(pwm + BCM2711_PWM_CONTROL) = 0;
     
+    *(pwm + BCM2711_PWM_CONTROL) = 0;
     wait_msec(2);
     
     *(pwm+BCM2711_PWM0_RANGE) = 0x264; // 44.1khz, Stereo, 8-bit (54Mhz / 44100 / 2)
@@ -62,8 +125,6 @@ static void audio_init(void)
           BCM2711_PWM1_ENABLE | 
           BCM2711_PWM0_USEFIFO | 
           BCM2711_PWM0_ENABLE | 1<<6;
-
-    wait_msec(2);
 }
 
 void playaudio_cpu()
@@ -77,6 +138,8 @@ void playaudio_cpu()
     unsigned int size = (long)&_binary_audio_bin_size;
     unsigned char *data = &(_binary_audio_bin_start[0]);
 
+    // Write data out to FIFO
+
     while (i < size) {
         status = *(pwm + BCM2711_PWM_STATUS);
         if (!(status & BCM2711_FULL1)) {
@@ -86,9 +149,6 @@ void playaudio_cpu()
             i++;
         }
         if ((status & ERRORMASK)) {
-            debugstr("error: ");
-            debughex(status);
-            debugcrlf();
             *(pwm+BCM2711_PWM_STATUS) = ERRORMASK;
         }
     }
@@ -98,13 +158,24 @@ void main()
 {
     fb_init();
 
-    debugstr("Initialising audio... ");
+    debugstr("Initialising audio unit... ");
     audio_init();
     debugstr("done"); debugcrlf();
 
-    debugstr("Starting to play sample using CPU"); debugcrlf();
+    debugstr("Playing sample using CPU... ");
     playaudio_cpu();
-    debugstr("CPU finished playing sample"); debugcrlf();
+    debugstr("done"); debugcrlf();
+
+    debugstr("Playing sample using DMA... ");
+    playaudio_dma();
+    debugstr("done"); debugcrlf();
+
+    debugstr("main() running still... ");
+    while (*(dma+DMA_CS) & 0x1) { // Wait for DMA transfer to finish - we could do anything here instead!
+       debugstr("x");
+       wait_msec(0x100000);
+    }
+    debugstr(" ----> finished");
  
     while(1);
 }