Allow noncontiguous pins in display

In the micro:bit v2 the LED matrix pins are not placed next to each
other. This change updates `display::control` so that it is configured
with arrays of pin IDs rather than start and end IDs.

Author: robyoung

src/display/control.rs

@@ -7,19 +7,23 @@
 use crate::pac;
 use tiny_led_matrix::DisplayControl;
 
-const fn bit_range(lo: usize, count: usize) -> u32 {
-    ((1 << count) - 1) << lo
+const fn pin_bits(pins: &[usize]) -> u32 {
+    let mut i: usize = 0;
+    let mut bits: u32 = 0;
+    while i < pins.len() {
+        bits |= 1 << pins[i];
+        i += 1;
+    }
+    bits
 }
 
 pub(crate) const MATRIX_COLS: usize = 9;
-const FIRST_COL_PIN: usize = 4;
-const LAST_COL_PIN: usize = FIRST_COL_PIN + MATRIX_COLS - 1;
-const COL_BITS: u32 = bit_range(FIRST_COL_PIN, MATRIX_COLS);
+const COLS: [usize; MATRIX_COLS] = [4, 5, 6, 7, 8, 9, 10, 11, 12];
+const COL_BITS: u32 = pin_bits(&COLS);
 
 pub(crate) const MATRIX_ROWS: usize = 3;
-const FIRST_ROW_PIN: usize = 13;
-const LAST_ROW_PIN: usize = FIRST_ROW_PIN + MATRIX_ROWS - 1;
-const ROW_BITS: u32 = bit_range(FIRST_ROW_PIN, MATRIX_ROWS);
+const ROWS: [usize; MATRIX_ROWS] = [13, 14, 15];
+const ROW_BITS: u32 = pin_bits(&ROWS);
 
 /// Wrapper for `nrf51::GPIO` for passing to the display code.
 ///
@@ -28,9 +32,14 @@ const ROW_BITS: u32 = bit_range(FIRST_ROW_PIN, MATRIX_ROWS);
 /// [`DisplayControl`]: tiny_led_matrix::DisplayControl
 pub(crate) struct MicrobitGpio<'a>(pub &'a pac::GPIO);
 
-/// Returns the GPIO pin numbers corresponding to the columns in a ColumnSet.
-fn column_pins(cols: u32) -> u32 {
-    cols << FIRST_COL_PIN
+/// Returns the GPIO pin numbers corresponding to the columns in a Columnt et.
+fn column_pins(mut cols: u32) -> u32 {
+    let mut result = 0u32;
+    for pin in COLS.iter() {
+        result |= (cols & 1) << pin;
+        cols >>= 1;
+    }
+    result
 }
 
 /// Implementation of [`DisplayControl`] for the micro:bit's GPIO peripheral.
@@ -44,23 +53,24 @@ fn column_pins(cols: u32) -> u32 {
 impl DisplayControl for MicrobitGpio<'_> {
     fn initialise_for_display(&mut self) {
         let gpio = &self.0;
-        for ii in FIRST_COL_PIN..=LAST_COL_PIN {
-            gpio.pin_cnf[ii].write(|w| w.dir().output());
+        for ii in COLS.iter() {
+            gpio.pin_cnf[*ii].write(|w| w.dir().output());
         }
-        for ii in FIRST_ROW_PIN..=LAST_ROW_PIN {
-            gpio.pin_cnf[ii].write(|w| w.dir().output());
+        for ii in ROWS.iter() {
+            gpio.pin_cnf[*ii].write(|w| w.dir().output());
         }
 
         // Set all cols high.
         gpio.outset
-            .write(|w| unsafe { w.bits((FIRST_COL_PIN..=LAST_COL_PIN).map(|pin| 1 << pin).sum()) });
+            .write(|w| unsafe { w.bits(COLS.iter().map(|pin| 1 << pin).sum()) });
     }
 
     fn display_row_leds(&mut self, row: usize, cols: u32) {
         let gpio = &self.0;
         // To light an LED, we set the row bit and clear the col bit.
-        let rows_to_set = 1 << (FIRST_ROW_PIN + row);
+        let rows_to_set = 1 << ROWS[row];
         let rows_to_clear = ROW_BITS ^ rows_to_set;
+
         let cols_to_clear = column_pins(cols);
         let cols_to_set = COL_BITS ^ cols_to_clear;