LPC1768: Add open drain pull up / pull down / etc modes (#484)

Author: multiplemonomials

targets/TARGET_NXP/TARGET_LPC17XX/TARGET_MBED_LPC1768/PinNames.h

@@ -122,12 +122,18 @@ typedef enum {
 #define I2C_SDA I2C_SDA2
 
 typedef enum {
-    PullUp = 0,
-    PullDown = 3,
-    PullNone = 2,
-    Repeater = 1,
-    OpenDrain = 4,
-    PullDefault = PullDown
+    PullUp = 0, ///< Pull up to VDD with internal resistor of between 59kOhm and 333kOhm. This is the default mode.
+    PullDown = 3, ///< Pull down to GND with internal resistor of between 33kOhm and 500kOhm.
+    PullNone = 2, ///< High impedance, no pull up or pull down
+    Repeater = 1, ///< AKA "keeper" mode. This keeps the pin in the current logic level state (high or low) to prevent it from floating
+
+    OpenDrain = 4,///< Open drain mode with pull-up (default)
+    OpenDrainPullUp = OpenDrain,
+    OpenDrainPullDown = OpenDrain | PullDown, ///< Open-drain mode with pull down
+    OpenDrainNoPull = OpenDrain | PullNone, ///< Open-drain mode with no pullup/pulldown
+    OpenDrainRepeater = OpenDrain | PullNone, ///< Open-drain mode with repeater/keeper
+
+    PullDefault = PullUp
 } PinMode;
 
 // version of PINCON_TypeDef using register arrays

targets/TARGET_NXP/TARGET_LPC17XX/pinmap.c

@@ -35,16 +35,23 @@ void pin_mode(PinName pin, PinMode mode) {
     uint32_t pin_number = (uint32_t)pin - (uint32_t)P0_0;
     int index = pin_number >> 5;
     int offset = pin_number & 0x1F;
-    uint32_t drain = ((uint32_t) mode & (uint32_t) OpenDrain) >> 2;
+    bool open_drain = (uint32_t) mode & (uint32_t) OpenDrain;
 
-    PINCONARRAY->PINMODE_OD[index] &= ~(drain << offset);
-    PINCONARRAY->PINMODE_OD[index] |= drain << offset;
-    
-    if (!drain) {
-        index = pin_number >> 4;
-        offset = (pin_number & 0xF) << 1;
-        
-        PINCONARRAY->PINMODE[index] &= ~(0x3 << offset);
-        PINCONARRAY->PINMODE[index] |= (uint32_t)mode << offset;
+    if(open_drain) {
+        PINCONARRAY->PINMODE_OD[index] |= 1 << offset;
+    }
+    else {
+        PINCONARRAY->PINMODE_OD[index] &= ~(1 << offset);
     }
+    
+    // Even if open drain mode is active, the normal pinmode is still used when the open drain pin is outputting a 1.
+    // So, always set the PINMODE register.
+    const uint8_t pinmode_sel_msk = 0x3;
+    uint8_t mode_no_drain = mode & pinmode_sel_msk;
+    
+    index = pin_number >> 4;
+    offset = (pin_number & 0xF) << 1;
+    
+    PINCONARRAY->PINMODE[index] &= ~(pinmode_sel_msk << offset);
+    PINCONARRAY->PINMODE[index] |= mode_no_drain << offset;
 }