SAMD20: More SERCOM USART configuration logic

arch/arm/src/samd/sam_lowputc.c

@@ -4,6 +4,15 @@
  *   Copyright (C) 2014 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
+ * References:
+ *   1. "Atmel SAM D20J / SAM D20G / SAM D20E ARM-Based Microcontroller
+ *      Datasheet", 42129J–SAM–12/2013
+ *   2. Atmel sample code.  This code has an ASF license with is compatible
+ *      with the NuttX BSD license, but includes the provision that this
+ *      code not be used in non-Atmel products.  That sample code was used
+ *      only as a reference so I believe that only the NuttX BSD license
+ *      applies.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
@@ -41,14 +50,23 @@
 
 #include <stdint.h>
 #include <assert.h>
+#include <errno.h>
+
+#include "up_arch.h"
 
 #include "sam_config.h"
+#include "chip/sam_pm.h"
+#include "chip/sam_usart.h"
 #include "sam_usart.h"
 
 /****************************************************************************
  * Pre-processor Definitions
  ****************************************************************************/
 
+#ifndef OK
+#  define OK 0
+#endif
+
 /****************************************************************************
  * Private Data
  ****************************************************************************/
@@ -57,17 +75,196 @@
  * Private Functions
  ****************************************************************************/
 
+/****************************************************************************
+ * Name: sam_wait_synchronization
+ *
+ * Description:
+ *   Wait until the SERCOM USART reports that it is synchronized.
+ *
+ ****************************************************************************/
+
+#ifdef HAVE_USART
+static void
+sam_wait_synchronization(const struct sam_usart_config_s * const config)
+{
+  while ((getreg16(config->base + SAM_USART_STATUS_OFFSET) & USART_STATUS_SYNCBUSY) != 0);
+}
+#endif
+
+/****************************************************************************
+ * Name: sam_gclk_configure
+ *
+ * Description:
+ *   Configure the SERCOM USART source clock.
+ *
+ ****************************************************************************/
+
+#ifdef HAVE_USART
+static inline int
+sam_gclk_configure(const struct sam_usart_config_s * const config)
+{
+#warning Missing logic
+  return -ENOSYS;
+}
+#endif
+
+/****************************************************************************
+ * Name: sam_usart_configure
+ *
+ * Description:
+ *   Configure the SERCOM USART operating mode (as a normal UART).
+ *
+ ****************************************************************************/
+
+#ifdef HAVE_USART
+static inline int
+sam_usart_configure(const struct sam_usart_config_s * const config)
+{
+  uint32_t ctrla;
+  uint32_t ctrlb;
+  uint32_t baud;
+
+  /* Check if baud is within the valid range. */
+
+  if (config->baud > (config->frequency >> 1))
+    {
+      return -ERANGE;
+    }
+
+  /* Calculate BAUD divider from the source clock frequency and desired baud */
+
+  baud = (config->frequency / (2 * config->baud)) - 1;
+
+  /* Verify that the calculated result is within range */
+
+  if (baud > UINT16_MAX)
+    {
+      return -ERANGE;
+    }
+
+  /* Wait until synchronization is complete */
+
+  sam_wait_synchronization(config);
+
+  /* Set baud val */
+
+  putreg16((uint16_t)baud, config->base + SAM_USART_BAUD_OFFSET);
+
+  /* Configure the USART CTRLA and CTRLB registers */
+
+  ctrla = (USART_CTRLA_MODE_INTUSART  | (uint32_t)config->muxconfig |
+           USART_CTRLA_ASYNCH | USART_CTRLA_CPOL_NORMAL |
+           USART_CTRLA_LSBFIRST);
+  ctrlb = (USART_CTRLB_TXEN | USART_CTRLB_RXEN);
+
+  /* Set the number of stop bits */
+
+  if (config->stopbits2)
+    {
+      ctrlb |= USART_CTRLB_SBMODE;
+    }
+
+  /* Set the USART word size */
+
+  switch (config->bits)
+    {
+      case 5:
+        ctrlb |= USART_CTRLB_CHSIZE_5BITS;
+        break;
+
+      case 6:
+        ctrlb |= USART_CTRLB_CHSIZE_6BITS;
+        break;
+
+      case 7:
+        ctrlb |= USART_CTRLB_CHSIZE_7BITS;
+        break;
+
+      default:
+      case 8:
+        break;
+
+      case 9:
+        ctrlb |= USART_CTRLB_CHSIZE_9BITS;
+        break;
+    }
+
+  /* Set parity mode */
+
+  switch (config->parity)
+    {
+      default:
+      case 0: /* None */
+        break;
+
+      case 1: /* Odd */
+        ctrlb |= USART_CTRLB_PODD;
+        /* Fall through */
+
+      case 2: /* Even */
+        ctrla |= USART_CTRLA_FORM_PARITY;
+        break;
+    }
+
+#if 0 /* Not supported */
+  /* Set run mode during device sleep */
+
+  if (config->runinstandby)
+    {
+      /* Enable in sleep mode */
+
+      ctrla |= USART_CTRLA_RUNSTDBY;
+    }
+#endif
+
+  /* Wait until synchronization is complete */
+
+  sam_wait_synchronization(config);
+
+  /* Write configuration to CTRLB */
+
+  putreg32(ctrlb, SAM_USART5_CTRLB);
+
+  /* Wait until synchronization is complete */
+
+  sam_wait_synchronization(config);
+
+  /* Write configuration to CTRLA */
+
+  putreg32(ctrlb, SAM_USART5_CTRLA);
+  return OK;
+}
+#endif
+
+/****************************************************************************
+ * Name: sam_pad_configure
+ *
+ * Description:
+ *   Configure the SERCOM USART pads.
+ *
+ ****************************************************************************/
+
+#ifdef HAVE_USART
+static inline int
+sam_pad_configure(const struct sam_usart_config_s * const config)
+{
+#warning Missing logic
+  return -ENOSYS;
+}
+#endif
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
 
-/************************************************************************************
+/****************************************************************************
  * Name: sam_lowsetup
  *
  * Description:
- *   Called at the very beginning of _start.  Performs low level initialization.
+ *   Called at the very beginning of _start.  Performs low level
+ *   initialization.
  *
- ************************************************************************************/
+ ****************************************************************************/
 
 void sam_lowsetup(void)
 {
@@ -75,17 +272,46 @@ void sam_lowsetup(void)
 }
 
 /****************************************************************************
- * Name: sam_usartconfig
+ * Name: sam_usart_initialize
  *
  * Description:
  *   Set the configuration of a SERCOM for provided USART configuration.
+ *   This configures the SERCOM as a USART, but does not configure USART
+ *   interrupts or enable the USART.
  *
  *****************************************************************************/
 
 #ifdef HAVE_USART
-void sam_usartconfig(const struct sam_usart_config_s *config)
+int sam_usart_initialize(const struct sam_usart_config_s * const config)
 {
-#warning Missing logic
+  uint32_t regval;
+  int ret;
+
+  /* Enable clocking to the SERCOM module in PM */
+
+  regval  = getreg32(SAM_PM_APBCMASK);
+  regval |= PM_APBCMASK_SERCOM(config->sercom);
+  putreg32(regval, SAM_PM_APBCMASK);
+
+  /* Configure the GCCLK for the SERCOM module */
+
+  ret = sam_gclk_configure(config);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
+  /* Set configuration according to the board configuration */
+
+  ret = sam_usart_configure(config);
+  if(ret < 0)
+    {
+      return ret;
+    }
+
+  /* Configure USART pins */
+
+  return sam_pad_configure(config);
 }
 #endif
 

arch/arm/src/samd/sam_lowputc.h

@@ -81,16 +81,18 @@ extern "C"
 void sam_lowsetup(void);
 
 /****************************************************************************
- * Name: sam_usartconfig
+ * Name: sam_usart_initialize
  *
  * Description:
  *   Set the configuration of a SERCOM for provided USART configuration.
+ *   This configures the SERCOM as a USART, but does not configure USART
+ *   interrupts or enable the USART.
  *
  *****************************************************************************/
 
 #ifdef HAVE_USART
 struct sam_usart_config_s;
-void sam_usartconfig(const struct sam_usart_config_s *config);
+int sam_usart_initialize(const struct sam_usart_config_s * const config);
 #endif
 
 /****************************************************************************

arch/arm/src/samd/sam_usart.c

@@ -73,6 +73,7 @@ const struct sam_usart_config_s g_usart0config =
   .pad2      = BOARD_SERCOM0_PINMAP_PAD2,
   .pad3      = BOARD_SERCOM0_PINMAP_PAD3,
   .muxconfig = BOARD_SERCOM0_MUXCONFIG,
+  .frequency = BOARD_SERCOM0_FREQUENCY,
   .base      = SAM_SERCOM0_BASE,
 };
 #endif
@@ -92,6 +93,7 @@ const struct sam_usart_config_s g_usart1config =
   .pad2      = BOARD_SERCOM1_PINMAP_PAD2,
   .pad3      = BOARD_SERCOM1_PINMAP_PAD3,
   .muxconfig = BOARD_SERCOM1_MUXCONFIG,   
+  .frequency = BOARD_SERCOM1_FREQUENCY,
   .base      = SAM_SERCOM1_BASE,
 };
 #endif
@@ -111,6 +113,7 @@ const struct sam_usart_config_s g_usart2config =
   .pad2      = BOARD_SERCOM2_PINMAP_PAD2,
   .pad3      = BOARD_SERCOM2_PINMAP_PAD3,
   .muxconfig = BOARD_SERCOM2_MUXCONFIG,
+  .frequency = BOARD_SERCOM2_FREQUENCY,
   .base      = SAM_SERCOM2_BASE,
 };
 #endif
@@ -130,6 +133,7 @@ const struct sam_usart_config_s g_usart3config =
   .pad2      = BOARD_SERCOM3_PINMAP_PAD2,
   .pad3      = BOARD_SERCOM3_PINMAP_PAD3,
   .muxconfig = BOARD_SERCOM3_MUXCONFIG,
+  .frequency = BOARD_SERCOM3_FREQUENCY,
   .base      = SAM_SERCOM3_BASE,
 };
 #endif
@@ -149,6 +153,7 @@ const struct sam_usart_config_s g_usart4config =
   .pad2      = BOARD_SERCOM4_PINMAP_PAD2,
   .pad3      = BOARD_SERCOM4_PINMAP_PAD3,
   .muxconfig = BOARD_SERCOM4_MUXCONFIG,
+  .frequency = BOARD_SERCOM4_FREQUENCY,
   .base      = SAM_SERCOM4_BASE,
 };
 #endif
@@ -168,6 +173,7 @@ const struct sam_usart_config_s g_usart5config =
   .pad2      = BOARD_SERCOM5_PINMAP_PAD2,
   .pad3      = BOARD_SERCOM5_PINMAP_PAD3,
   .muxconfig = BOARD_SERCOM5_MUXCONFIG,
+  .frequency = BOARD_SERCOM5_FREQUENCY,
   .base      = SAM_SERCOM5_BASE,
 };
 #endif

arch/arm/src/samd/sam_usart.h

@@ -91,6 +91,7 @@ struct sam_usart_config_s
   port_pinset_t pad2; /* Pin configuration for PAD2 */
   port_pinset_t pad3; /* Pin configuration for PAD3 */
   uint32_t muxconfig; /* Pad multiplexing configuration */
+  uint32_t frequency; /* Source clock frequency */
   uintptr_t base;     /* SERCOM base address */
 };