Incorporate review comments

Author: Martin Crossley

pio/seven_segment/7_segment.c

@@ -7,7 +7,18 @@ const PIO pio = pio0;
 const uint first_segment_pin = 8;   // gpio 15-8 = segments E,D,B,G,A,C,F,dp
 const uint first_digit_pin = 16;    // gpio 19-16 = common anodes 4,3,2,1
 
-//                      EDBGACF.       bit ordering depends on your display and wiring
+// By convention the segments are labelled as follows:
+//
+//  AAAA
+// F    B
+// F    B
+//  GGGG
+// E    C
+// E    C
+//  DDDD  .
+
+// You can define a custom bit pattern like this:
+// the order here is    EDBGACF.  but should match the way you wire up the GPIOs
 const uint32_t Pico = 0b10111010 << 24 |    // 'P'
                       0b10000000 << 16 |    // 'i'
                       0b11010000 <<  8 |    // 'c'

pio/seven_segment/README.adoc

@@ -7,7 +7,7 @@ The total current required is typically more than the GPIO pins can supply so yo
 
 The PIO code uses four `side-set` pins to control the digit multiplex lines and displays the segment patterns received on the FIFO. It uses a non-blocking PULL to keep showing the same segments until the CPU sends new data.
 
-The provided example uses spells out the word **Pico** and then counts from 0 to 9999.
+The provided example spells out the word **Pico** and then counts from 0 to 9999.
 
 == Wiring information
 Connect the display to your board using a circuit like the one below, making any changes for your display and transistors.

pio/seven_segment/pio_7_segment_library/7_segment_lib.c

@@ -22,12 +22,17 @@ static const uint8_t segments[] = {
 //
 uint32_t int_to_seven_segment (int num) {
     uint32_t word = 0;
-    if (num == 0) {
-        word = segments[0];
-    } else {
-        for (int bitshift = 0; bitshift < 32 && num > 0; bitshift += 8) {
-            word |= segments[num % 10] << bitshift;
-            num /= 10;
+    if (num > 9999) {
+        // argument exceeds 4 digits: display an 'E' symbol
+        word = 0b11011010
+    } else { 
+        if (num == 0) {
+            word = segments[0];
+        } else {
+            for (int bitshift = 0; bitshift < 32 && num > 0; bitshift += 8) {
+                word |= segments[num % 10] << bitshift;
+                num /= 10;
+            }
         }
     }
     return word;