Add DMA information : always finding the right way to use a free DMA channel

src/mailbox.c

@@ -265,3 +265,23 @@ int mbox_open() {
 void mbox_close(int file_desc) {
   close(file_desc);
 }
+
+//https://github.com/sarfata/pi-blaster/pull/38#discussion_r28041695
+unsigned get_dma_channels(int file_desc)
+{
+   int i=0;
+   unsigned p[32];
+   p[i++] = 0; // size
+   p[i++] = 0x00000000; // process request
+
+   p[i++] = 0x60001; // (the tag id)
+   p[i++] = 4; // (size of the buffer)
+   p[i++] = 0; // (size of the data)
+   p[i++] = 0; // response buffer
+
+   p[i++] = 0x00000000; // end tag
+   p[0] = i*sizeof *p; // actual size
+   
+   mbox_property(file_desc, p);
+   return p[5];
+}

src/mailbox.h

@@ -46,3 +46,4 @@ void *unmapmem(void *addr, unsigned size);
 unsigned execute_code(int file_desc, unsigned code, unsigned r0, unsigned r1, unsigned r2, unsigned r3, unsigned r4, unsigned r5);
 unsigned execute_qpu(int file_desc, unsigned num_qpus, unsigned control, unsigned noflush, unsigned timeout);
 unsigned qpu_enable(int file_desc, unsigned enable);
+unsigned get_dma_channels(int file_desc);

src/rpidma.c

@@ -32,7 +32,7 @@ char InitDma(void *FunctionTerminate)
 		printf("Failed to open mailbox\n");
 		return(0);
 	}
-	
+	printf("DMA used : %x\n",get_dma_channels(mbox.handle));
 	mbox.mem_ref = mem_alloc(mbox.handle, NUM_PAGES* PAGE_SIZE, PAGE_SIZE, mem_flag);
 	/* TODO: How do we know that succeeded? */
 	//printf("mem_ref %x\n", mbox.mem_ref);