Add DELAY_US_MULT, for use in generalizing delay_us().

The delay_us() implementation multiplies its specified delay target by
a fixed constant in order to turn it into a busy-loop.  This magic
number doesn't work properly when the clock configuration isn't the
same as a stock LeafLabs board.  Add DELAY_US_MULT to the MCU-specific
configuration in stm32.h in order to allow other chips to use delay_us().

2 files changed, 9 insertions, 8 deletions

diff --git a/libmaple/delay.h b/libmaple/delay.h
index 56611a5..dd68ec6 100644
--- a/libmaple/delay.h
+++ b/libmaple/delay.h
@@ -4,6 +4,7 @@
  */
 
 #include "libmaple_types.h"
+#include "stm32.h"
 
 #ifndef _DELAY_H_
 #define _DELAY_H_
@@ -11,17 +12,10 @@
 /**
  * @brief Delay the given number of microseconds.
  *
- * Note that this function currently assumes you are on a LeafLabs
- * board, and will only work properly if you follow the LeafLabs RCC
- * configuration.
- *
  * @param us Number of microseconds to delay.
  */
 static inline void delay_us(uint32 us) {
-    /* TODO this makes unwarranted assumptions about the RCC
-     * config; add a hook so users can make their own decisions. */
-    /* So (2^32)/12 micros max, or less than 6 minutes */
-    us *= 12;
+    us *= DELAY_US_MULT;
 
     /* fudge for function call overhead  */
     us--;
diff --git a/libmaple/stm32.h b/libmaple/stm32.h
index d7e946e..9d2ed99 100644
--- a/libmaple/stm32.h
+++ b/libmaple/stm32.h
@@ -32,11 +32,16 @@
     /* SRAM size, in bytes */
     #define SRAM_SIZE             0x5000
 
+    /* Multiplier to convert microseconds into loop iterations in
+     * delay_us() (See delay.h) */
+    #define DELAY_US_MULT             12
+
 #elif defined(MCU_STM32F103ZE)
     /* e.g., LeafLabs Maple Native */
 
     #define NR_GPIO_PORTS              7
     #define SRAM_SIZE            0x10000
+    #define DELAY_US_MULT             12
 
 #elif defined(MCU_STM32F103CB)
     /* e.g., LeafLabs Maple Mini */
@@ -47,12 +52,14 @@
     #define NR_GPIO_PORTS              3
 
     #define SRAM_SIZE             0x5000
+    #define DELAY_US_MULT             12
 
 #elif defined(MCU_STM32F103RE)
     /* e.g., LeafLabs Maple RET6 edition */
 
     #define NR_GPIO_PORTS              4
     #define SRAM_SIZE            0x10000
+    #define DELAY_US_MULT             12
 
 #else