bsp/atsam: Optionally use DMA for UART Rx

If the system is busy with other interrupts and the UART is set to a
fast baud rate, it's possible to loose UART interrupts and therefore
characters. This allows to optionally enable a DMA for the UARTs so that
a number of lost interrupts can be tolerated.

The number of DMAs on this chip is limited and not not all applications
need that feature. Therefore the DMA is disabled by default.

Close #4578

1 files changed, 177 insertions, 5 deletions

diff --git a/bsps/arm/atsam/console/console.c b/bsps/arm/atsam/console/console.c
index a5a981fb3e..5ef4327e11 100644
--- a/bsps/arm/atsam/console/console.c
+++ b/bsps/arm/atsam/console/console.c
@@ -16,6 +16,7 @@
 #include <bsp/irq.h>
 #include <bsp/fatal.h>
 #include <rtems/console.h>
+#include <rtems/seterr.h>
 
 #include <rtems/termiostypes.h>
 
@@ -23,6 +24,13 @@
 
 #include <unistd.h>
 
+#define UART_RX_DMA_BUF_SIZE 32l
+
+typedef struct {
+  char buf[UART_RX_DMA_BUF_SIZE];
+  LinkedListDescriporView3 desc;
+} atsam_uart_rx_dma;
+
 typedef struct {
   rtems_termios_device_context base;
   Uart *regs;
@@ -32,6 +40,11 @@ typedef struct {
   bool is_usart;
 #ifdef ATSAM_CONSOLE_USE_INTERRUPTS
   bool transmitting;
+  bool rx_dma_enabled;
+  uint32_t rx_dma_channel;
+  atsam_uart_rx_dma *rx_dma;
+  char *volatile*rx_dma_da;
+  char *rx_next_read_pos;
 #endif
 } atsam_uart_context;
 
@@ -109,12 +122,27 @@ static void atsam_uart_interrupt(void *arg)
   Uart *regs = ctx->regs;
   uint32_t sr = regs->UART_SR;
 
-  while ((sr & UART_SR_RXRDY) != 0) {
-    char c = (char) regs->UART_RHR;
+  if (!ctx->rx_dma_enabled) {
+    while ((sr & UART_SR_RXRDY) != 0) {
+      char c = (char) regs->UART_RHR;
+
+      rtems_termios_enqueue_raw_characters(tty, &c, 1);
+
+      sr = regs->UART_SR;
+    }
+  } else {
+    while (*ctx->rx_dma_da != ctx->rx_next_read_pos) {
+      char c;
 
-    rtems_termios_enqueue_raw_characters(tty, &c, 1);
+      c = *ctx->rx_next_read_pos;
 
-    sr = regs->UART_SR;
+      ++ctx->rx_next_read_pos;
+      if (ctx->rx_next_read_pos >= &ctx->rx_dma->buf[UART_RX_DMA_BUF_SIZE]) {
+        ctx->rx_next_read_pos = &ctx->rx_dma->buf[0];
+      }
+
+      rtems_termios_enqueue_raw_characters(tty, &c, 1);
+    }
   }
 
   if (ctx->transmitting && (sr & UART_SR_TXEMPTY) != 0) {
@@ -196,6 +224,118 @@ static bool atsam_uart_set_attributes(
   return true;
 }
 
+static void atsam_uart_disable_rx_dma(atsam_uart_context *ctx)
+{
+  if (ctx->rx_dma) {
+    rtems_cache_coherent_free(ctx->rx_dma);
+    ctx->rx_dma = NULL;
+  }
+
+  if (ctx->rx_dma_channel != XDMAD_ALLOC_FAILED) {
+    XDMAD_FreeChannel(&XDMAD_Instance, ctx->rx_dma_channel);
+  }
+
+  ctx->rx_dma_enabled = false;
+}
+
+static rtems_status_code atsam_uart_enable_rx_dma(atsam_uart_context *ctx)
+{
+  eXdmadRC rc;
+  int channel_id;
+
+  if (ctx->rx_dma_enabled) {
+    return RTEMS_SUCCESSFUL;
+  }
+
+  /*
+   * Make sure everything is in a clean default state so that the cleanup works
+   * in an error case.
+   */
+  ctx->rx_dma = NULL;
+  ctx->rx_dma_channel = XDMAD_ALLOC_FAILED;
+
+  ctx->rx_dma = rtems_cache_coherent_allocate(sizeof(*ctx->rx_dma), 0, 0);
+  if (ctx->rx_dma == NULL) {
+    atsam_uart_disable_rx_dma(ctx);
+    return RTEMS_NO_MEMORY;
+  }
+
+  ctx->rx_next_read_pos = &ctx->rx_dma->buf[0];
+
+  ctx->rx_dma_channel = XDMAD_AllocateChannel(
+    &XDMAD_Instance,
+    XDMAD_TRANSFER_MEMORY,
+    ctx->id
+  );
+
+  if (ctx->rx_dma_channel == XDMAD_ALLOC_FAILED) {
+    atsam_uart_disable_rx_dma(ctx);
+    return RTEMS_IO_ERROR;
+  }
+
+  rc = XDMAD_PrepareChannel(&XDMAD_Instance, ctx->rx_dma_channel);
+  if (rc != XDMAD_OK) {
+    atsam_uart_disable_rx_dma(ctx);
+    return RTEMS_IO_ERROR;
+  }
+
+  channel_id = ctx->rx_dma_channel & 0xff;
+  ctx->rx_dma_da =
+    (char *volatile*) &XDMAD_Instance.pXdmacs->XDMAC_CHID[channel_id].XDMAC_CDA;
+
+  ctx->rx_dma->desc.mbr_nda = (uint32_t)&ctx->rx_dma->desc;
+  ctx->rx_dma->desc.mbr_ubc =
+    1 |
+    XDMA_UBC_NVIEW_NDV3 |
+    XDMA_UBC_NDE_FETCH_EN |
+    XDMA_UBC_NDEN_UPDATED |
+    XDMA_UBC_NSEN_UPDATED;
+  ctx->rx_dma->desc.mbr_sa = (uint32_t) &ctx->regs->UART_RHR;
+  ctx->rx_dma->desc.mbr_da = (uint32_t) &ctx->rx_dma->buf[0];
+  ctx->rx_dma->desc.mbr_cfg =
+    XDMAC_CC_TYPE_PER_TRAN |
+    XDMAC_CC_MBSIZE_SINGLE |
+    XDMAC_CC_DSYNC_PER2MEM |
+    XDMAC_CC_SWREQ_HWR_CONNECTED |
+    XDMAC_CC_MEMSET_NORMAL_MODE |
+    XDMAC_CC_CSIZE_CHK_1 |
+    XDMAC_CC_DWIDTH_BYTE |
+    XDMAC_CC_SIF_AHB_IF1 |
+    XDMAC_CC_DIF_AHB_IF1 |
+    XDMAC_CC_SAM_FIXED_AM |
+    XDMAC_CC_DAM_UBS_AM |
+    XDMAC_CC_PERID(XDMAIF_Get_ChannelNumber(ctx->id, XDMAD_TRANSFER_RX));
+  ctx->rx_dma->desc.mbr_bc = UART_RX_DMA_BUF_SIZE - 1;
+  ctx->rx_dma->desc.mbr_ds = 0;
+  ctx->rx_dma->desc.mbr_sus = 0;
+  ctx->rx_dma->desc.mbr_dus = 0;
+
+  rc = XDMAD_ConfigureTransfer(
+    &XDMAD_Instance,
+    ctx->rx_dma_channel,
+    NULL,
+    XDMAC_CNDC_NDE_DSCR_FETCH_EN |
+    XDMAC_CNDC_NDVIEW_NDV3 |
+    XDMAC_CNDC_NDDUP_DST_PARAMS_UPDATED |
+    XDMAC_CNDC_NDSUP_SRC_PARAMS_UPDATED,
+    (uint32_t)&ctx->rx_dma->desc,
+    0);
+  if (rc != XDMAD_OK) {
+    atsam_uart_disable_rx_dma(ctx);
+    return RTEMS_IO_ERROR;
+  }
+
+  rc = XDMAD_StartTransfer(&XDMAD_Instance, ctx->rx_dma_channel);
+  if (rc != XDMAD_OK) {
+    atsam_uart_disable_rx_dma(ctx);
+    return RTEMS_IO_ERROR;
+  }
+
+  ctx->rx_dma_enabled = true;
+
+  return RTEMS_SUCCESSFUL;
+}
+
 static bool atsam_uart_first_open(
   rtems_termios_tty *tty,
   rtems_termios_device_context *base,
@@ -246,6 +386,10 @@ static void atsam_uart_last_close(
   rtems_interrupt_handler_remove(ctx->irq, atsam_uart_interrupt, tty);
 #endif
 
+  if (ctx->rx_dma_enabled) {
+    atsam_uart_disable_rx_dma(ctx);
+  }
+
   if (!ctx->console) {
     PMC_DisablePeripheral(ctx->id);
   }
@@ -296,13 +440,41 @@ static int atsam_uart_read(rtems_termios_device_context *base)
 }
 #endif
 
+#ifdef ATSAM_CONSOLE_USE_INTERRUPTS
+static int atsam_uart_ioctl(
+  rtems_termios_device_context *base,
+  ioctl_command_t               request,
+  void                         *buffer
+)
+{
+  atsam_uart_context *ctx = (atsam_uart_context *) base;
+  rtems_status_code sc;
+
+  switch (request) {
+    case ATSAM_UART_ENABLE_RX_DMA:
+      sc = atsam_uart_enable_rx_dma(ctx);
+      if (sc != RTEMS_SUCCESSFUL) {
+        rtems_set_errno_and_return_minus_one(EIO);
+      } else {
+        ctx->rx_dma_enabled = true;
+      }
+      break;
+    default:
+      rtems_set_errno_and_return_minus_one(EINVAL);
+  }
+
+  return 0;
+}
+#endif
+
 static const rtems_termios_device_handler atsam_uart_handler = {
   .first_open = atsam_uart_first_open,
   .last_close = atsam_uart_last_close,
   .write = atsam_uart_write,
   .set_attributes = atsam_uart_set_attributes,
 #ifdef ATSAM_CONSOLE_USE_INTERRUPTS
-  .mode = TERMIOS_IRQ_DRIVEN
+  .mode = TERMIOS_IRQ_DRIVEN,
+  .ioctl = atsam_uart_ioctl,
 #else
   .poll_read = atsam_uart_read,
   .mode = TERMIOS_POLLED