Editing Embedded Programming Tips and Tricks
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| − | =Fast Division= | + | ===Fast Division=== |
On microcontrollers without a divide instruction very fast division can be done by bit shifting a variable right.<br> | On microcontrollers without a divide instruction very fast division can be done by bit shifting a variable right.<br> | ||
Each shift does a divide by two.<br> | Each shift does a divide by two.<br> | ||
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Also be sure the variable size is large enough to store the multiplied value.<br> | Also be sure the variable size is large enough to store the multiplied value.<br> | ||
| − | |||
| − | When writing embedded code you will quite often need to | + | ===Timed Events Using Interrupts=== |
| − | Over your entire project there maybe many different | + | |
| + | When writing embedded code you will quite often need to run code at a regular interval. (for example flashing an led. | ||
| + | Over your entire project there maybe many different events you wish to occur at different rates. | ||
To do this it can be useful to dedicate one of the microcontrollers hardware timers to perform all these timing tasks. | To do this it can be useful to dedicate one of the microcontrollers hardware timers to perform all these timing tasks. | ||
| − | + | It is bad practice to put lots of code inside an interrupt handler so the best approach is to set flags and then test these flags inside your main program loop. | |
| − | |||
| − | |||
| − | + | Such a system might look like this | |
| + | ==AVR== | ||
<pre> | <pre> | ||
| − | + | uint16_t clk1000ms=1; | |
| − | + | uint16_t clk100ms=1; | |
| + | uint8_t clk10ms=1; | ||
| − | |||
| − | |||
| − | |||
ISR (TIMER0_OVF_vect) | ISR (TIMER0_OVF_vect) | ||
{ | { | ||
| − | if (clk1000ms!= | + | if (clk1000ms!=0) |
{ | { | ||
clk1000ms++; | clk1000ms++; | ||
| − | if (clk1000ms>=10001) clk1000ms= | + | if (clk1000ms>=10001) clk1000ms=0; |
} | } | ||
| − | if (clk100ms!= | + | if (clk100ms!=0) |
{ | { | ||
clk100ms++; | clk100ms++; | ||
| − | if (clk100ms>=1001) | + | if (clk100ms>=1001) clk500ms=0; |
} | } | ||
| − | if (clk10ms!= | + | if (clk10ms!=0) |
{ | { | ||
clk10ms++; | clk10ms++; | ||
| − | if (clk10ms>=101) clk10ms= | + | if (clk10ms>=101) clk10ms=0; |
} | } | ||
// Timer clock is 1mhz, timer is 8bit. | // Timer clock is 1mhz, timer is 8bit. | ||
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{ | { | ||
| − | if (clk1000ms== | + | if (clk1000ms==0) |
{ | { | ||
// put code here to run every second | // put code here to run every second | ||
| − | clk1000ms = | + | clk1000ms = 1; |
} | } | ||
| − | if (clk100ms== | + | if (clk100ms==0) |
{ | { | ||
// put code here to run 10 times a second | // put code here to run 10 times a second | ||
| − | clk100ms = | + | clk100ms = 1; |
} | } | ||
| − | if (clk10ms== | + | if (clk10ms==0) |
{ | { | ||
// put code here to run 100 times a second | // put code here to run 100 times a second | ||
| − | clk10ms = | + | clk10ms = 1; |
} | } | ||
} | } | ||
</pre> | </pre> | ||
