timers progress

examples code cleanup, more descriptive comments, more notes

2 files changed, 62 insertions, 37 deletions

diff --git a/notes/timers.txt b/notes/timers.txt
index 3e6bb9c..3f5b9f4 100644
--- a/notes/timers.txt
+++ b/notes/timers.txt
@@ -12,54 +12,69 @@ Timer2,Ch 3+4 are D0 and D1, which conflict with Serial2. USART should work
 fine as long as pins aren't in output mode? and timers should work fine if
 Serial2 isn't in use?
 
+Caveats
+------------------------------------------------------------------------------
+There are probably subtle bugs with the way register settings get read in; eg,
+it is often required to have the counter fully overflow before new settings
+come into effect?
+Getting really good timing is still an art, not a science here... usually you 
+need to fiddle with an oscilloscope and the exact overflow/compare numbers to
+get just the right time values.
+Any other interrupts (SysTick, USB, Serial, etc) can blow away all the nice 
+timing stuff.
+
 Misc Notes
 ------------------------------------------------------------------------------
-implementation with case/switch in the interrupt handlers doesn't work; a lot
+Implementation with case/switch in the interrupt handlers doesn't work; a lot
 of the time multiple interrupt flags are active at the same time (or become
 active?)
 
 TODO
 ------------------------------------------------------------------------------
+- document carefully (eg, determine clock-wise and overflow-wise behavior for
+  each function)
+- track down and handle all pin conflicts
+- implement the update interrupt as a "5th channel"
+- "pulse in" stuff, both c and c++
 - function to read out CCR registers
 - allow comparison output to the pin (a la PWM)
 - additional modes and configuration (up, down, up/down, etc)
-- Wirish (C++) higher level implementation
-- implement the update interrupt as a "5th channel"
-- track down and handle all pin conflicts
-- document
 
 Possible Wirish implementation
 ------------------------------------------------------------------------------
-This recent implementation seems pretty clean:
+Inspired by Timer1 Library for arduino
 http://arduino.cc/pipermail/developers_arduino.cc/2010-June/002845.html
 
-        class Timer1Class {
-        public:
-            static void (*isrCompareA)(void);
-            static void (*isrCompareB)(void);
-
-            static const uint8_t PRESCALE1 = 1;
-            static const uint8_t PRESCALE8 = 2;
-            static const uint8_t PRESCALE64 = 3;
-            static const uint8_t PRESCALE256 = 4;
-            static const uint8_t PRESCALE1024 = 5;
+        class HardwareTimer {
 
-            const static uint8_t NORMAL = 0;
-            const static uint8_t CTC = 4;
+        public:
 
-            void setPrescaleFactor(uint8_t factor);
-            void setMode(uint8_t mode);
-            uint16_t read();
-            void write(uint16_t val);
-            void writeCompareA(uint16_t val);
-            void writeCompareB(uint16_t val);
-            void attachCompareAInterrupt(void (*f)(void));
-            void attachCompareBInterrupt(void (*f)(void));
-            void detachCompareAInterrupt();
-            void detachCompareBInterrupt();
+            void pause();
+            void resume();
+            void setPrescaleFactor(uint8 factor);
+            void setOverflow(uint16 val); // truncates to overflow
+            void setCount(uint16 val);    // truncates to overflow
+            uint16 getCount();
+            uint16 setPeriod(uint32 microseconds); // tries to set prescaler and overflow wisely; returns overflow
+            void setMode(uint8 mode);
+            void setCompare1(uint16 val); // truncates to overflow
+            void setCompare2(uint16 val); // truncates to overflow
+            void setCompare3(uint16 val); // truncates to overflow
+            void setCompare4(uint16 val); // truncates to overflow
+            void attachCompare1Interrupt(void (*f)(void));
+            void attachCompare2Interrupt(void (*f)(void));
+            void attachCompare3Interrupt(void (*f)(void));
+            void attachCompare4Interrupt(void (*f)(void));
+            void detachCompare1Interrupt();
+            void detachCompare2Interrupt();
+            void detachCompare3Interrupt();
+            void detachCompare4Interrupt();
         };
 
-        extern Timer1Class Timer1;
+        HardwareTimer Timer1 = HardwareTimer(1);
+        HardwareTimer Timer2 = HardwareTimer(2);
+        HardwareTimer Timer3 = HardwareTimer(3);
+        HardwareTimer Timer4 = HardwareTimer(4);
 
 Here's one of the more standard libaries out there:
 http://www.arduino.cc/playground/Code/Timer1
diff --git a/notes/vga.txt b/notes/vga.txt
index 2230f57..d75281a 100644
--- a/notes/vga.txt
+++ b/notes/vga.txt
@@ -1,32 +1,42 @@
 
-classic digitalWrite() gives ~500ns pulse time (2MHz)
+Notes on GPIO Writing
+------------------------------------------------------------------------------
+Classic digitalWrite() gives ~500ns pulse time (2MHz)
 
 gpio_write_bit() is about 360ns (2.78MHz)
 
-writing to GPIO?_BASE is about 60ns (16.6MHz -> 18MHz)
+Writing to GPIO?_BASE is about 60ns (16.6MHz -> 18MHz)
 
-pwm write 0x0001 is about 30ns (33MHz)
+pwm write 0x0001 is about 30ns (33MHz) with prescaler as 1 (default)
 pwm write 0x0001 is about 14ns (72MHz) with prescaler as 0 (!)
 
-1/25.125MHz = 39.72ns
+VGA Timing
+------------------------------------------------------------------------------
+1/25.125MHz = 39.72ns (640x480 pixel clock)
 
-crude 640x480 directions:
-    www.epanorama.net/documents/pc/vga_timing.html
+Crude 640x480 directions:
+    From www.epanorama.net/documents/pc/vga_timing.html
     480 lines
     31.77 us horizontal line length -> 2287.44 clock cycles -> 2287
     3.77 us sync period -> 271 clocks -> 271
     1.89 us front porch? -> 136 clocks -> 136
     25.17 us video -> 1812.24 clocks -> 1812
    
-    so... 
+    So... 
     2287 reload 
     271  1: Hsync high
     407  2: Video on
     2219 3: Video off
     2287 4: Hsync low
 
-    vertically, it's 
+    Vertically, it's 
     480 lines active video
     11 lines front porch
     2 lines Vsync (low)
     31 lines back porch
+
+Currently, setting vs. clearing GPIO registers seems to take a different amount
+of time? Or perhaps i'm not analyzing branching correctly. Regardless, if you
+SET 100x times then UNSET on one line, then UNSET 100x then SET the next line,
+the two changes in color will generally not line up. 
+