diff options
Diffstat (limited to 'notes')
| -rw-r--r-- | notes/timers.txt | 77 | ||||
| -rw-r--r-- | notes/vga.txt | 32 |
2 files changed, 109 insertions, 0 deletions
diff --git a/notes/timers.txt b/notes/timers.txt new file mode 100644 index 0000000..3e6bb9c --- /dev/null +++ b/notes/timers.txt @@ -0,0 +1,77 @@ + +Each timer (1-4) has 4 capture/compare channels (1-4). These are directly used +by PWM but have a ton of other possible functionality. The STM32 implementation +is particularly complicated with, eg, the ability to chain together timers + +Timer1 is an "advanced timer" with many more features. I think if we use just +the "Capture and compare interrupt", and enable MOE during initialization +everything will be ok. There are seperate Break, Update, and Trigger interrupts +as well that we will ignore for now. + +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? + +Misc Notes +------------------------------------------------------------------------------ +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 +------------------------------------------------------------------------------ +- 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: +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; + + const static uint8_t NORMAL = 0; + const static uint8_t CTC = 4; + + 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(); + }; + + extern Timer1Class Timer1; + +Here's one of the more standard libaries out there: +http://www.arduino.cc/playground/Code/Timer1 + + void initialize(long microseconds=1000000); + void start(); + void stop(); + void restart(); + void setPeriod(long microseconds); + void pwm(char pin, int duty, long microseconds=-1); + void setPwmDuty(char pin, int duty); + void disablePwm(char pin); + void attachInterrupt(void (*isr)(), long microseconds=-1); + void detachInterrupt(); + diff --git a/notes/vga.txt b/notes/vga.txt new file mode 100644 index 0000000..2230f57 --- /dev/null +++ b/notes/vga.txt @@ -0,0 +1,32 @@ + +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) + +pwm write 0x0001 is about 30ns (33MHz) +pwm write 0x0001 is about 14ns (72MHz) with prescaler as 0 (!) + +1/25.125MHz = 39.72ns + +crude 640x480 directions: + 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... + 2287 reload + 271 1: Hsync high + 407 2: Video on + 2219 3: Video off + 2287 4: Hsync low + + vertically, it's + 480 lines active video + 11 lines front porch + 2 lines Vsync (low) + 31 lines back porch |