Implement non-stop DMA mode (circular) for the F1x DMA driver.

nuttx/arch/arm/src/stm32/stm32f10xxx_dma.c

@@ -90,6 +90,7 @@ struct stm32_dma_s
 {
   uint8_t        chan;     /* DMA channel number (0-6) */
   uint8_t        irq;      /* DMA channel IRQ number */
+  bool           nonstop;  /* Stream is configured in non-stopping mode */
   sem_t          sem;      /* Used to wait for DMA channel to become available */
   uint32_t       base;     /* DMA register channel base address */
   dma_callback_t callback; /* Callback invoked when the DMA completes */
@@ -303,14 +304,10 @@ static int stm32_dmainterrupt(int irq, void *context)
     }
   dmach = &g_dma[chndx];
 
-  /* Get the interrupt status (for this channel only) -- not currently used */
+  /* Get the interrupt status (for this channel only) */
 
   isr = dmabase_getreg(dmach, STM32_DMA_ISR_OFFSET) & DMA_ISR_CHAN_MASK(dmach->chan);
 
-  /* Disable the DMA channel */
-
-  stm32_dmachandisable(dmach);
-
   /* Invoke the callback */
 
   if (dmach->callback)
@@ -493,6 +490,7 @@ void stm32_dmasetup(DMA_HANDLE handle, uint32_t paddr, uint32_t maddr, size_t nt
   ccr    &=  (DMA_CCR_MEM2MEM|DMA_CCR_PL_MASK|DMA_CCR_MSIZE_MASK|DMA_CCR_PSIZE_MASK|
               DMA_CCR_MINC|DMA_CCR_PINC|DMA_CCR_CIRC|DMA_CCR_DIR);
   regval |= ccr;
+  dmach->nonstop = (ccr & DMA_CCR_CIRC) != 0;
   dmachan_putreg(dmach, STM32_DMACHAN_CCR_OFFSET, regval);
 }
 
@@ -528,14 +526,30 @@ void stm32_dmastart(DMA_HANDLE handle, dma_callback_t callback, void *arg, bool
   ccr  = dmachan_getreg(dmach, STM32_DMACHAN_CCR_OFFSET);
   ccr |= DMA_CCR_EN;
 
-  /* Once half of the bytes are transferred, the half-transfer flag (HTIF) is
-   * set and an interrupt is generated if the Half-Transfer Interrupt Enable
-   * bit (HTIE) is set. At the end of the transfer, the Transfer Complete Flag
-   * (TCIF) is set and an interrupt is generated if the Transfer Complete
-   * Interrupt Enable bit (TCIE) is set.
-   */
+  if (!dmach->nonstop)
+    {
+      /* Once half of the bytes are transferred, the half-transfer flag (HTIF) is
+       * set and an interrupt is generated if the Half-Transfer Interrupt Enable
+       * bit (HTIE) is set. At the end of the transfer, the Transfer Complete Flag
+       * (TCIF) is set and an interrupt is generated if the Transfer Complete
+       * Interrupt Enable bit (TCIE) is set.
+       */
+
+      ccr |= (half ? (DMA_CCR_HTIE|DMA_CCR_TEIE) : (DMA_CCR_TCIE|DMA_CCR_TEIE));
+
+    }
+  else
+    {
+      /* In nonstop mode, when the transfer completes it immediately resets
+       * and starts again.  The transfer-complete interrupt is thus always
+       * enabled, and the half-complete interrupt can be used in circular 
+       * mode to determine when the buffer is half-full, or in double-buffered
+       * mode to determine when one of the two buffers is full.
+       */
+
+      ccr |= (half ? DMA_CCR_HTIE : 0) | DMA_CCR_TCIE | DMA_CCR_TEIE;
+    }
 
-  ccr |= (half ? (DMA_CCR_HTIE|DMA_CCR_TEIE) : (DMA_CCR_TCIE|DMA_CCR_TEIE));
   dmachan_putreg(dmach, STM32_DMACHAN_CCR_OFFSET, ccr);
 }