Diff: flexiBar.cpp

Revision:

8:8a2d07e4a8c3

Child:

9:d87a0d02a0ac

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+++ b/flexiBar.cpp	Mon Oct 23 19:10:39 2017 +0000
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+/*
+    Project: FlexiBarDemo
+    File: flexiBar.cpp
+    Function: flexiBar (v. 1.1)
+    Created by: Dr. C. S. Tritt, 10/22/17
+
+    This function displays an integer value (range 0 to 9) on the specified bar
+    graph display. 
+    
+    Precondition(s):
+    
+        Physical bar graph display correctly wired to digital output pins.
+        BusOut object that collects display output pins.
+    
+    Postcondition(s):
+    
+        Bar graph display is left showing the appropriate output.
+    
+    Arguments/Parameters:
+    
+        int value - Value to be displayed. Range -1 to 9, inclusive.
+        BusOut &theBar - Bus created from connected GPIO output pins.
+        bool single - Single vs. stacked display format. True indicates single.
+        bool active - Active high flag. True indicates active high.
+    
+    Returns (& Error Handling):
+    
+        0 - Normal operation.
+        1 - Error, value out of range.
+        
+    Notes:
+    
+    To assure display is operational, at least one bar will always be lit
+    (0 is indicated by a single bar and 9 by 10 bars). A special case is the 
+    the value -1, which will light no bars.
+
+    I previously thought pow would be better than left shift (<<), but now I see
+    that left shift really is the best approach.
+
+    Mbed objects generally must be passed by reference (with &). This prevents
+    there possibly two or more instances of the objects possibly having 
+    conflicting states.
+
+    Pass theBar (rather than using the global symbol) for flexibility.
+
+    Note there are 2 returns in this function! One for value being out of range
+    errors. The other for no error.
+*/
+#include "mbed.h"
+
+int flexiBar(int value, BusOut &theBar, bool single, bool active)
+{
+
+    if (value < -1 || value > 9) return 1; // Indicate value out-of-range error.
+
+    int output; // Use variable to make active low case easy to compute.
+
+    if (value == -1) {
+        output = 0;  // Special case of all bars off.
+    } else {
+        if (single) {
+            output = 1 << value; // Light single bars by shifting 1 left.
+        } else {
+            output = (1 << (value + 1)) - 1; // Light a stack of bars.
+        }
+    }
+
+    if (active) { // Deal with active low vs. active high.
+        theBar = output;
+    } else {
+        theBar = ~output; // Invert bits for active low.
+    }
+    return 0; //
+}
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