SysTick refactor.

For the changelog:

* util.h is free of __read(), __write(), etc. macros.

* systick_resume() was renamed systick_enable().

3 files changed, 81 insertions, 56 deletions

diff --git a/libmaple/systick.c b/libmaple/systick.c
index b9a52c1..c04f4f3 100644
--- a/libmaple/systick.c
+++ b/libmaple/systick.c
@@ -26,44 +26,46 @@
  * @brief System timer interrupt handler and initialization routines
  */
 
-#include "libmaple.h"
 #include "systick.h"
 
-#define SYSTICK_RELOAD          0xE000E014  // Reload value register
-#define SYSTICK_CNT             0xE000E018  // Current value register
-#define SYSTICK_CALIB           0xE000E01C  // Calibration value register
-
-#define SYSTICK_SRC_HCLK        BIT(2)    // Use core clock
-#define SYSTICK_TICKINT         BIT(1)    // Interrupt on systick countdown
-#define SYSTICK_ENABLE          BIT(0)    // Turn on the counter
-
 volatile uint32 systick_timer_millis;
 
+/**
+ * @brief Initialize and enable SysTick.
+ *
+ * Clocks the system timer with the core clock, turns it on, and
+ * enables interrupts.
+ *
+ * @param reload_val Appropriate reload counter to tick every 1 ms.
+ */
 void systick_init(uint32 reload_val) {
-    /* Set the reload counter to tick every 1ms  */
-    __write(SYSTICK_RELOAD, reload_val);
-
-    /* Clock the system timer with the core clock and turn it on,
-     * interrrupt every 1ms to keep track of millis() */
-    __write(SYSTICK_CSR, SYSTICK_SRC_HCLK |
-            SYSTICK_ENABLE                |
-            SYSTICK_TICKINT);
+    SYSTICK_BASE->RVR = reload_val;
+    systick_enable();
 }
 
+/**
+ * Clock the system timer with the core clock, but don't turn it
+ * on or enable interrupt.
+ */
 void systick_disable() {
-    /* clock the system timer with the core clock, but don't turn it
-       on or enable interrupt. */
-    __write(SYSTICK_CSR, SYSTICK_SRC_HCLK);
+    SYSTICK_BASE->CSR = SYSTICK_CSR_CLKSOURCE_CORE;
 }
 
-void systick_resume() {
-    /* re-enable init registers without changing reload val */
-    __write(SYSTICK_CSR, SYSTICK_SRC_HCLK |
-            SYSTICK_ENABLE                |
-            SYSTICK_TICKINT);
+/**
+ * Clock the system timer with the core clock and turn it on;
+ * interrupt every 1 ms, for systick_timer_millis.
+ */
+void systick_enable() {
+    /* re-enables init registers without changing reload val */
+    SYSTICK_BASE->CSR = (SYSTICK_CSR_CLKSOURCE_CORE   |
+                         SYSTICK_CSR_ENABLE           |
+                         SYSTICK_CSR_TICKINT_PEND);
 }
 
-/** SysTick interrupt handler.  Bumps up the tick counter. */
+/*
+ * SysTick ISR
+ */
+
 void __exc_systick(void) {
     systick_timer_millis++;
 }
diff --git a/libmaple/systick.h b/libmaple/systick.h
index 33a3cf8..35b4cb9 100644
--- a/libmaple/systick.h
+++ b/libmaple/systick.h
@@ -31,30 +31,60 @@
 #ifndef _SYSTICK_H_
 #define _SYSTICK_H_
 
-#include "libmaple.h"
+#include "libmaple_types.h"
+#include "util.h"
 
 #ifdef __cplusplus
 extern "C"{
 #endif
 
-#define SYSTICK_CSR             0xE000E010  // Control and status register
-#define SYSTICK_CNT             0xE000E018  // Current value register
+/** SysTick register map type */
+typedef struct systick_reg_map {
+    __io uint32 CSR;            /**< Control and status register */
+    __io uint32 RVR;            /**< Reload value register */
+    __io uint32 CNT;            /**< Current value register ("count") */
+    __io uint32 CVR;            /**< Calibration value register */
+} systick_reg_map;
 
-#define SYSTICK_CSR_COUNTFLAG   BIT(16)
+/** SysTick register map base pointer */
+#define SYSTICK_BASE                    ((struct systick_reg_map*)0xE000E010)
 
-/** System elapsed time in milliseconds */
+/*
+ * Register bit definitions.
+ */
+
+/* Control and status register */
+
+#define SYSTICK_CSR_COUNTFLAG           BIT(16)
+#define SYSTICK_CSR_CLKSOURCE           BIT(2)
+#define SYSTICK_CSR_CLKSOURCE_EXTERNAL  0
+#define SYSTICK_CSR_CLKSOURCE_CORE      BIT(2)
+#define SYSTICK_CSR_TICKINT             BIT(1)
+#define SYSTICK_CSR_TICKINT_PEND        BIT(1)
+#define SYSTICK_CSR_TICKINT_NO_PEND     0
+#define SYSTICK_CSR_ENABLE              BIT(0)
+#define SYSTICK_CSR_ENABLE_MULTISHOT    BIT(0)
+#define SYSTICK_CSR_ENABLE_DISABLED     0
+
+/* Calibration value register */
+
+#define SYSTICK_CVR_NOREF               BIT(31)
+#define SYSTICK_CVR_SKEW                BIT(30)
+#define SYSTICK_CVR_TENMS               0xFFFFFF
+
+/** System elapsed time, in milliseconds */
 extern volatile uint32 systick_timer_millis;
 
 void systick_init(uint32 reload_val);
 void systick_disable();
-void systick_resume();
+void systick_enable();
 
 static inline uint32 systick_get_count(void) {
-    return __read(SYSTICK_CNT);
+    return SYSTICK_BASE->CNT;
 }
 
 static inline uint32 systick_check_underflow(void) {
-    return (__read(SYSTICK_CSR) & SYSTICK_CSR_COUNTFLAG);
+    return SYSTICK_BASE->CSR & SYSTICK_CSR_COUNTFLAG;
 }
 
 #ifdef __cplusplus
diff --git a/libmaple/util.h b/libmaple/util.h
index 25dd56e..aff70e1 100644
--- a/libmaple/util.h
+++ b/libmaple/util.h
@@ -23,14 +23,12 @@
  *****************************************************************************/
 
 /**
- *  @file util.h
- *
- *  @brief Various macros and utility procedures.
+ * @file util.h
+ * @brief Miscellaneous utility macros and procedures.
  */
 
 #include "libmaple_types.h"
 
-/* Generally "useful" utility procedures  */
 #ifndef _UTIL_H_
 #define _UTIL_H_
 
@@ -38,33 +36,23 @@
 extern "C"{
 #endif
 
-/* Debug configuration */
-#define DEBUG_NONE      0
-#define DEBUG_FAULT     1
-#define DEBUG_ALL       2
-
-#ifndef DEBUG_LEVEL
-#define DEBUG_LEVEL DEBUG_ALL
-#endif
+/*
+ * Bit manipulation
+ */
 
 #define BIT(shift)                     (1UL << (shift))
 #define BIT_MASK_SHIFT(mask, shift)    ((mask) << (shift))
-
-/* Return bits m to n of x  */
+/* Bits m to n of x */
 #define GET_BITS(x, m, n) ((((uint32)x) << (31 - (n))) >> ((31 - (n)) + (m)))
+#define IS_POWER_OF_TWO(v)  (v && !(v & (v - 1)))
 
 /*
  * Register reads and writes
  */
 
-#define __set_bits(addr, mask)   (*(volatile uint32*)(addr) |= (uint32)(mask))
-#define __clear_bits(addr, mask) (*(volatile uint32*)(addr) &= (uint32)~(mask))
-#define __get_bits(addr, mask)   (*(volatile uint32*)(addr) & (uint32)(mask))
 #define __read(reg)              (*(volatile uint32*)(reg))
 #define __write(reg, value)      (*(volatile uint32*)(reg) = (value))
 
-#define IS_POWER_OF_TWO(v)  (v && !(v & (v - 1)))
-
 /*
  * Failure routines
  */
@@ -77,13 +65,20 @@ void throb(void);
  * Asserts and debug levels
  */
 
+#define DEBUG_NONE      0
+#define DEBUG_FAULT     1
+#define DEBUG_ALL       2
+
+#ifndef DEBUG_LEVEL
+#define DEBUG_LEVEL DEBUG_ALL
+#endif
+
 #if DEBUG_LEVEL >= DEBUG_ALL
 #define ASSERT(exp)                              \
     if (exp) {                                   \
     } else {                                     \
         _fail(__FILE__, __LINE__, #exp);         \
     }
-
 #else
 #define ASSERT(exp) (void)((0))
 #endif
@@ -94,7 +89,6 @@ void throb(void);
     } else {                                    \
         _fail(__FILE__, __LINE__, #exp);        \
     }
-
 #else
 #define ASSERT_FAULT(exp) (void)((0))
 #endif
@@ -104,4 +98,3 @@ void throb(void);
 #endif
 
 #endif
-