Now setting DMA transfer on CPU core 2 to show both cores free

part10-multicore/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);

part10-multicore/kernel.c

@@ -3,7 +3,10 @@
 #include "multicore.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
@@ -31,8 +34,71 @@
 #define BCM2711_FULL1 0x1
 #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; // Points to PWM_FIFO
+    playback_cb.txfr_len = size * 4; // They're unsigned ints now, not unsigned chars
+    playback_cb.stride = 0x00;
+    playback_cb.nextconbk = 0x00; // Don't loop
+    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)
 {   
@@ -94,29 +160,36 @@ void playaudio_cpu()
 
 void core2_main(void)
 {
-    clear_core2();           // Only run once
+    clear_core2();                // Only run once
 
-    debugstr("Playing on CPU Core #2... ");
+    debugstr("Playing on CPU Core #2 using DMA... ");
-    playaudio_cpu();
+    playaudio_dma();
-    debugstr(" done"); debugcrlf();
+    debugstr("done"); debugcrlf();
+
+    debugstr("core2_main() running still... ");
+    while (*(dma+DMA_CS) & 0x1) { // Wait for DMA transfer to finish - we could do anything here instead!
+       wait_msec(0x47FFFF);
+       debugstr("o");             // Print an o roughly every 4.5 seconds
+    }
+    debugstr(" ----> finished");
 }
 
 void core1_main(void)
 {
-    clear_core1();           // Only run once
+    clear_core1();                // Only run once
 
     debugstr("Playing on CPU Core #1... ");
     playaudio_cpu();
     debugstr(" done"); debugcrlf();
 
-    start_core2(core2_main); // Kick it off on core 2
+    start_core2(core2_main);      // Kick it off on core 2
 }
 
 void core0_main(void)
 {
     while (1) {
        wait_msec(0x100000);
-       debugstr("x");
+       debugstr("x");             // Print an x roughly every 1 second
     }
 }
 
@@ -128,6 +201,6 @@ void main(void)
     audio_init();
     debugstr("done"); debugcrlf();
 
-    start_core1(core1_main); // Kick it off on core 1
+    start_core1(core1_main);      // Kick it off on core 1
-    core0_main();            // Loop endlessly, printing x's
+    core0_main();                 // Loop endlessly, printing x's
 }