changed all timers to count-down, prose cleanup

CooperativeMultitasking.md

@@ -1245,7 +1245,7 @@ void stateCode(char event) {
     // ....
   }
 }
-
+```
 
 In the above example, you could equally well have set the timer to start at zero
 and increment until it hits the desired limit (100 in this case).
@@ -1262,7 +1262,8 @@ behalf of the tasks......
 Let's create a centralized service called `setTimer(timer_index, timer_count)`. 
 
 A task can call this service with a unique `timer_index` and a requested count. The
-`timer_irq()` will then count out the ticks on behalf of the task, and when the tick
+`timer_irq()` uses a pool of timer registers, and will count out the ticks 
+on behalf of the task, and when the tick
 count is finished, the `timer_irq()` code can generate a unique event, perhaps
 `EVT_TIMER_n`. 
 
@@ -1290,14 +1291,14 @@ void stateCode(char event) {
 }
 ```
 
-This makes the state code much simpler to read, 
+This makes the state code simpler to read, 
 hiding all the increments/decrements and limit testing.
 
 The overhead for this ends up in the `timer_irq()` code, 
 and might look something like this:
 
 ```C
-static unsigned int timers[NUM_TIMERS];
+static uint16 timers[NUM_TIMERS];
 #define EVT_TIMER_OFFSET 100
 enum {EVENT_TIMER_1=EVT_TIMER_OFFSET, EVENT_TIMER_2, EVENT_TIMER_3}; // 100, 101...
 enum {TIMER_1, TIMER_2, TIMER_3};   // 0,1,2,....
@@ -1321,7 +1322,7 @@ void setTimer(int timerIndex, unsigned int timerCount) {
 <details><summary>Reality Check</summary>
 On a typical microcontroller running at 24MHz, with 5 timers, this adds about
 2 microseconds of extra time to the `timer_irq()` code, which typically runs every 
-10 or 100msec. It considerably simplifies the task code, makes it more legible
+10 or 100msec. It simplifies the task code, makes it more legible
 and probably reduces bugs that may appear by duplication of code.
 
 Another possible design for timers is to have the main `timer_isr()` increment
@@ -1502,22 +1503,22 @@ void main(void) {
 /*********** task code, with states ************/
 enum {LED_ON, LED_OFF};
 enum {RTB_IDLE, RTB_ON};    // states
-static uint8 rtbState           = RTB_IDLE;
-static uint16 rtbTimerCount     = 0;
-const uint16 BUTTON_LED_ON_TIME = 150;
+static uint8 rtbState            = RTB_IDLE;
+static uint16 rtbTimerCount      = 0;
+const  uint16 BUTTON_LED_ON_TIME = 150;
 
 void respondToButtonTask(uint8 evt) {
   switch(rtbState) {
     case RTB_IDLE:
       if (evt == EVT_BUTTON) {
         rtbState      = RTB_ON;
-        rtbTimerCount = 0;
+        rtbTimerCount = BUTTON_LED_ON_TIME;
         gpio_set(LED, LED_ON);
       }
       break;
     case RTB_ON:
       if (evt == EVT_TICK) {
-        if (++rtbTimerCount > BUTTON_LED_ON_TIME) {
+        if (--rtbTimerCount == 0) {
           gpio_set(LED, LED_OFF);
           rtbState = RTB_IDLE;
         }
@@ -1526,9 +1527,9 @@ void respondToButtonTask(uint8 evt) {
     }
 }
 
-const uint16 LED_ON_TIME  = 150;
-const uint16 LED_OFF_TIME = 50;
-static uint8 ledState       = LED_OFF;
+const int LED_ON_TIME  = 150;
+const int LED_OFF_TIME = 50;
+static uint8  ledState      = LED_OFF;
 static uint16 ledTimerCount = 0;
 
 void ledTask(uint8 evt) {
@@ -1537,14 +1538,14 @@ void ledTask(uint8 evt) {
       if (evt == EVT_TICK) {
         if (++ledTimerCount > LED_OFF_TIME) {
           gpio_set(LED2, LED_ON);
-          ledTimerCount = 0;
+          ledTimerCount = LED_ON_TIME;
           ledState      = LED_ON;
         }
       }
       break;
     case LED_ON:
       if (evt == EVT_TICK) {
-        if (++ledTimerCount > LED_ON_TIME) {
+        if (--ledTimerCount == 0) {
           gpio_set(LED2, LED_OFF);
           ledTimerCount = 0;
           ledState      = LED_OFF;
@@ -1631,6 +1632,7 @@ void rtbTaskCode(char event) {
       break;
     case STATE_FLASHING:
       // count down flashCount, toggle LED halfway through
+      // effectively creating a substate
       if (event == EVT_TICK) {
         if (--flashCount == 0) {
           setLED(OFF);
@@ -1728,7 +1730,7 @@ a subroutine, it's allowed to return a value
 
 ![cd-eject task uses sendMessage() to call a sibling task](sendMessage.png)
 
-This of course means that the prototype for task functions would change from 
+To return a value means that the prototype for task functions would change from 
 
 ```C
 void taskCode(uint8 event);
@@ -1746,12 +1748,12 @@ uint8 SendMessage(int8 taskPointer(uint8), uint8 message) {
 
 ### Usage
 
-Why might one want to send a *message* between tasks?
+Why might one want to *send a message* between tasks?
 
 Suppose you have a rotary encoder, which sends quadrant signals, which need
 to be interpreted as *clockwise* and *counter clockwise*. You could have one
 task devoted to determining the direction of the knob 
-(and [debouncing](#debouncing)), and have it send clean 
+(and [debouncing](#debouncing)), and have it *send* (or *post*) clean 
 EVT_CW and EVT_CCW *messages* to its sibgling tasks.
 
 Another possible use of *messages* is to create alternate souces of input.
@@ -1774,7 +1776,7 @@ assignment was to code up a simulated automobile entertainment system, which inc
 - task blue light to show bluetooth connectivity
 - volume up/down sense and display
 - radio channel select buttons
-  - step single freq, or high-speed scan
+  - step single the radio frequency, or high-speed scan
 - power on/off management
 - remote control of volume/radio-select from the steering wheel (uart link)
 - backlight for night-time viewing (auto sense from a light sensor)

build/demo.stm32f0xx.c

@@ -127,13 +127,13 @@ void respondToButtonTask(uint8 evt) {
     case RTB_IDLE:
       if (evt == EVT_BUTTON) {
         rtbState      = RTB_ON;
-        rtbTimerCount = 0;
+        rtbTimerCount = BUTTON_LED_ON_TIME;
         gpio_set(LED, LED_ON);
       }
       break;
     case RTB_ON:
       if (evt == EVT_TICK) {
-        if (++rtbTimerCount > BUTTON_LED_ON_TIME) {
+        if (--rtbTimerCount == 0) {
           gpio_set(LED, LED_OFF);
           rtbState = RTB_IDLE;
         }
@@ -144,7 +144,7 @@ void respondToButtonTask(uint8 evt) {
 
 const int LED_ON_TIME  = 150;
 const int LED_OFF_TIME = 50;
-static uint8 ledState       = LED_OFF;
+static uint8  ledState      = LED_OFF;
 static uint16 ledTimerCount = 0;
 
 void ledTask(uint8 evt) {
@@ -153,14 +153,14 @@ void ledTask(uint8 evt) {
       if (evt == EVT_TICK) {
         if (++ledTimerCount > LED_OFF_TIME) {
           gpio_set(LED2, LED_ON);
-          ledTimerCount = 0;
+          ledTimerCount = LED_ON_TIME;
           ledState      = LED_ON;
         }
       }
       break;
     case LED_ON:
       if (evt == EVT_TICK) {
-        if (++ledTimerCount > LED_ON_TIME) {
+        if (--ledTimerCount == 0) {
           gpio_set(LED2, LED_OFF);
           ledTimerCount = 0;
           ledState      = LED_OFF;