optimized the LED and buzzer wiring

* since we use timer 3 exclusively for the buzzer but trigger the pin
  using an IRQ handler, there is no longer any need to occupy a high-resolution
  pin for the buzzer.
* PD5 became a new high resolution LED
* PD0 became the new buzzer pin
* rearranged the pins used for the different LEDs so that the distribution
  of high-resolution LEDs is symmetric
* Timer 0 is no longer used/modified by setting LEDs.
  This avoids some workarounds as timer 0 is also used by tmk's timer module.
* The song routines could be slightly improved using the timer module.
* documented the LED and buzzer pinout in README

7 files changed, 52 insertions, 104 deletions

diff --git a/README.md b/README.md
index 36f36ca..0516060 100644
--- a/README.md
+++ b/README.md
@@ -113,11 +113,21 @@ Now, solder wires *on the backside* of the PCBs to the following pins of the for
 
 ![8212](docs/8212.jpg)
 
-These wires connect to the Teensy in the following order: __FIXME__
+These wires connect to the Teensy in the following order:
+
+8212 Pin | Teensy Pin
+-------- | ----------
+4        | PB5
+6        | PD1
+8        | PB7
+10       | PB4
+15       | PB6
+17       | PD2
+21       | PD3
 
 Desolder the buzzer's 390R resistor and connect the side *facing away* from it
 to a jumper cable.
-It will connect to pin __FIXME__ of the Teensy.
+It will connect to pin PD0 of the Teensy.
 
 Desolder the IFFS cable.
 
diff --git a/command.c b/command.c
index 6827706..cb0c270 100644
--- a/command.c
+++ b/command.c
@@ -38,7 +38,7 @@ bool command_extra(uint8_t code)
             dprintf("new keyclick mode: %u\n", keyclick_mode);
             /* FIXME: Perhaps do this in matrix_scan() */
             keyclick_solenoid_set(false);
-            pwm_pb5_set_tone(0);
+            pwm_pd0_set_tone(0);
             /* update the keyclick mode LED */
             led_set(host_keyboard_leds());
             return true;
diff --git a/led.c b/led.c
index c7e5933..0d92563 100644
--- a/led.c
+++ b/led.c
@@ -40,33 +40,28 @@ void led_set(uint8_t usb_led)
     else
         PORTD |= (1 << PD3);
 
-    /*
-     * 1st LED on first row (G00).
-     *
-     * NOTE: This will automatically disable PWM mode, so it will not
-     * interfere with timer 0 and tmk's timer module.
-     */
-    pwm_pd0_set_led(usb_led & (1 << USB_LED_NUM_LOCK) ? 255 : 0);
+    /* 1st LED on first row (G00). */
+    pwm_pb5_set_led(usb_led & (1 << USB_LED_NUM_LOCK) ? 255 : 0);
 
     /* 2nd LED on first row (G01): Highlight keyclick mode. */
-    pwm_pb7_set_led(keyclick_mode*255/(KEYCLICK_MAX-1));
+    pwm_pd1_set_led(keyclick_mode*255/(KEYCLICK_MAX-1));
 
     /* 3rd LED on the first row (G02) */
-    pwm_pd1_set_led(usb_led & (1 << USB_LED_COMPOSE) ? 255 : 0);
+    pwm_pb7_set_led(usb_led & (1 << USB_LED_COMPOSE) ? 255 : 0);
 
     /*
      * 4th LED (G03) are currently not triggerable via USB.
      * Could be triggered as the "backlight".
      */
-    pwm_pb6_set_led(0);
+    pwm_pb4_set_led(0);
 
     /* 5th LED on the first row (G04) */
-    pwm_pb4_set_led(usb_led & (1 << USB_LED_SCROLL_LOCK) ? 255 : 0);
+    pwm_pb6_set_led(usb_led & (1 << USB_LED_SCROLL_LOCK) ? 255 : 0);
 
     /*
      * 6th LED on the first row (G53).
      *
-     * Triggering this LED (PD2) will also enable the buzzer (PB5),
+     * Triggering this LED (PD2) will also enable the buzzer (PD0),
      * so we have got a way to beep from userspace (see ./k7637-beep.sh).
      *
      * The original firmware also had the error display on G53
@@ -74,9 +69,9 @@ void led_set(uint8_t usb_led)
      */
     if (usb_led & (1 << USB_LED_KANA)) {
         PORTD &= ~(1 << PD2);
-        pwm_pb5_set_tone(2200);
+        pwm_pd0_set_tone(2200);
     } else {
         PORTD |= (1 << PD2);
-        pwm_pb5_set_tone(0);
+        pwm_pd0_set_tone(0);
     }
 }
diff --git a/matrix.c b/matrix.c
index 5c4ecbd..cbb011d 100644
--- a/matrix.c
+++ b/matrix.c
@@ -143,7 +143,7 @@ uint8_t matrix_scan(void)
 
             case KEYCLICK_BUZZER:
                 if (matrix_debouncing_pressed_keys > matrix_pressed_keys) {
-                    pwm_pb5_set_tone(550);
+                    pwm_pd0_set_tone(550);
                     keyclick_time = timer_read();
                 }
                 break;
@@ -229,7 +229,7 @@ uint8_t matrix_scan(void)
 
             case KEYCLICK_BUZZER:
                 if (!(host_keyboard_leds() & (1 << USB_LED_KANA)))
-                    pwm_pb5_set_tone(0);
+                    pwm_pd0_set_tone(0);
                 break;
 
             default:
diff --git a/pwm.c b/pwm.c
index 97c3dac..82fd106 100644
--- a/pwm.c
+++ b/pwm.c
@@ -97,47 +97,6 @@ static const uint16_t pwm_table16[256] PROGMEM = {
 };
 
 /**
- * Configure a PWM pin of Timer 0 (8-bit resolution).
- *
- * @note Timer 0 is used by tmk's timer module as well.
- * You can therefore only temporarilly PWM-modulate using timer 0
- * (ie. NOT during matrix scanning), cannot use any timer module functions
- * and should call timer_init() afterwards.
- * This can be easily resolved by using pwm_pb5_set_led() for one of the LEDs
- * and redistribute all the LED.
- * The buzzer can then use the no longer used PD0 since it's manually
- * IRQ-triggered anyway.
- *
- * @param channel Channel to initialize.
- *     0 (OC0A/PB7), 1 (OC0B/PD0)
- */
-static void pwm_timer0_init(uint8_t channel)
-{
-    /* Fast PWM on OC0x, inverted duty cycle, TOP = 0xFF */
-    TCCR0A |= (0b11 << (3-channel)*2) | 0b11;
-    /* no prescaling */
-    TCCR0B = 0b00000001;
-}
-
-void pwm_pd0_set_led(uint8_t brightness)
-{
-    switch (brightness) {
-        case 0:
-            TCCR0A &= ~0b00110000;
-            PORTD |= (1 << PD0);
-            break;
-        case 255:
-            TCCR0A &= ~0b00110000;
-            PORTD &= ~(1 << PD0);
-            break;
-        default:
-            pwm_timer0_init(1);
-            OCR0B = pgm_read_byte(&pwm_table8[brightness]);
-            break;
-    }
-}
-
-/**
  * Configure a PWM pin of Timer 1 (16-bit resolution).
  *
  * @param channel Channel to initialize.
@@ -262,24 +221,22 @@ void pwm_pd1_set_led(uint8_t brightness)
 /**
  * Set a LED by position in the first row.
  *
- * @bug The pins used should be rescrambled after we freed PD0.
- *
  * @param led LED to set (0-4).
  * @param brightness Brightness level to set.
  */
 void pwm_set_led(uint8_t led, uint8_t brightness)
 {
      switch (led) {
-         case 0: pwm_pd0_set_led(brightness); break;
-         case 1: pwm_pb7_set_led(brightness); break;
-         case 2: pwm_pd1_set_led(brightness); break;
-         case 3: pwm_pb6_set_led(brightness); break;
-         case 4: pwm_pb4_set_led(brightness); break;
+         case 0: pwm_pb5_set_led(brightness); break;
+         case 1: pwm_pd1_set_led(brightness); break;
+         case 2: pwm_pb7_set_led(brightness); break;
+         case 3: pwm_pb4_set_led(brightness); break;
+         case 4: pwm_pb6_set_led(brightness); break;
      }
 }
 
 /**
- * Play a tone on PB5 (the buzzer).
+ * Play a tone on PD0 (the buzzer).
  *
  * @note This uses timer 3 with an IRQ, even though we cannot
  * use one of the Timer 3 PWM pins -- they are required for matrix
@@ -305,7 +262,7 @@ void pwm_set_led(uint8_t led, uint8_t brightness)
  *
  * @param freq Frequency to play. If 0, disables the buzzer.
  */
-void pwm_pb5_set_tone(uint16_t freq)
+void pwm_pd0_set_tone(uint16_t freq)
 {
     if (!freq) {
         /*
@@ -343,5 +300,5 @@ void pwm_pb5_set_tone(uint16_t freq)
 
 ISR(TIMER3_COMPA_vect, ISR_NOBLOCK)
 {
-    PORTB ^= (1 << PB5);
+    PORTD ^= (1 << PD0);
 }
diff --git a/pwm.h b/pwm.h
index f1e0d3f..4a68f4b 100644
--- a/pwm.h
+++ b/pwm.h
@@ -20,7 +20,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <stdint.h>
 
-void pwm_pd0_set_led(uint8_t brightness);
 void pwm_pd1_set_led(uint8_t brightness);
 void pwm_pb4_set_led(uint8_t brightness);
 void pwm_pb5_set_led(uint8_t brightness);
@@ -29,6 +28,6 @@ void pwm_pb7_set_led(uint8_t brightness);
 
 void pwm_set_led(uint8_t led, uint8_t brightness);
 
-void pwm_pb5_set_tone(uint16_t freq);
+void pwm_pd0_set_tone(uint16_t freq);
 
 #endif
diff --git a/song.c b/song.c
index 4abbb03..d58ff16 100644
--- a/song.c
+++ b/song.c
@@ -193,11 +193,13 @@ void song_play_ruinen(void)
 {
     /* could be activated due to keyclick mode */
     keyclick_solenoid_set(false);
-    pwm_pb5_set_tone(0);
+    pwm_pd0_set_tone(0);
 
     uint8_t i = 0;
     for (long unsigned int cur_note = 0; cur_note < sizeof(song_ruinen)/sizeof(song_ruinen[0]); cur_note++) {
-        pwm_pb5_set_tone(pgm_read_word(&song_ruinen[cur_note].freq));
+        uint16_t cur_note_time = timer_read();
+
+        pwm_pd0_set_tone(pgm_read_word(&song_ruinen[cur_note].freq));
 
         uint8_t max_brightness = ((uint32_t)pgm_read_word(&song_ruinen[cur_note].freq)*255)/600;
         uint16_t fade_dur = pgm_read_word(&song_ruinen[cur_note].dur)/2/(max_brightness+1);
@@ -206,14 +208,6 @@ void song_play_ruinen(void)
             delay_long(fade_dur);
         }
 
-        /*
-         * The fade duration is probably not very precise, so compensate for it.
-         *
-         * FIXME: Once timer 0 is freed, we should use timer_read() and timer_elapsed()
-         * which will be more precise.
-         */
-        delay_long(pgm_read_word(&song_ruinen[cur_note].dur) - fade_dur*(max_brightness+1)*2);
-
         for (int16_t brightness = max_brightness; brightness >= 0; brightness--) {
             pwm_set_led(i % 5, brightness);
             delay_long(fade_dur);
@@ -221,12 +215,14 @@ void song_play_ruinen(void)
 
         if (pgm_read_word(&song_ruinen[cur_note].freq))
             i++;
-    }
 
-    pwm_pb5_set_tone(0);
+        /* The fade duration is probably not very precise, so compensate for it. */
+        uint16_t elapsed = timer_elapsed(cur_note_time);
+        if (elapsed < pgm_read_word(&song_ruinen[cur_note].dur))
+            delay_long(pgm_read_word(&song_ruinen[cur_note].dur) - elapsed);
+    }
 
-    /* we screwed up timer 0 settings and they are also used by the timer module */
-    timer_init();
+    pwm_pd0_set_tone(0);
 
     /* restore the previous lock lights */
     led_set(host_keyboard_leds());
@@ -414,7 +410,7 @@ void song_play_kitt(void)
 {
     /* could be activated due to keyclick mode */
     keyclick_solenoid_set(false);
-    pwm_pb5_set_tone(0);
+    pwm_pd0_set_tone(0);
 
     int16_t i;
 
@@ -423,38 +419,29 @@ void song_play_kitt(void)
         song_larsen_light(i);
 
     long unsigned int cur_note = 0;
-    uint16_t cur_note_dur = 0;
+    uint16_t cur_note_time = timer_read();
 
     int8_t dir = 1;
     for (i = 0; cur_note < sizeof(song_knight_rider)/sizeof(song_knight_rider[0]); i += dir) {
-        /*
-         * FIXME: Once we freed up timer 0 by rearranging the LED pins,
-         * it might be more precise to use timer_read()/timer_elapsed() to wait for the next note.
-         */
-        if (cur_note_dur < LARSEN_CURVE_STEP) {
-            cur_note_dur = pgm_read_word(&song_knight_rider[cur_note].dur);
-            pwm_pb5_set_tone(pgm_read_word(&song_knight_rider[cur_note].freq));
-        }
+        pwm_pd0_set_tone(pgm_read_word(&song_knight_rider[cur_note].freq));
 
         song_larsen_light(i);
 
-        cur_note_dur -= LARSEN_CURVE_STEP;
-        if (cur_note_dur < LARSEN_CURVE_STEP)
-            cur_note++;
-
         if (i == sizeof(song_larsen_curve)-1 || (dir < 0 && i == 0))
             dir *= -1;
+
+        if (timer_elapsed(cur_note_time) >= pgm_read_word(&song_knight_rider[cur_note].dur)) {
+            cur_note_time = timer_read();
+            cur_note++;
+        }
     }
 
-    pwm_pb5_set_tone(0);
+    pwm_pd0_set_tone(0);
 
     /* fade out larsen light */
     while (i < sizeof(song_larsen_curve)*3/2)
         song_larsen_light(i++);
 
-    /* we screwed up timer 0 settings and they are also used by the timer module */
-    timer_init();
-
     /* restore the previous lock lights */
     led_set(host_keyboard_leds());
 }