54 lines
1.4 KiB
C
54 lines
1.4 KiB
C
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/** \file
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\brief Delay routines, AVR specific part.
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*/
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#if defined TEACUP_C_INCLUDE && defined __AVR__
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#include <util/delay_basic.h>
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#if F_CPU < 4000000UL
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#error Delay functions on AVR only work with F_CPU >= 4000000UL
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#endif
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/** Delay in microseconds.
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\param delay Time to wait in microseconds.
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Calibrated in SimulAVR.
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Accuracy on 20 MHz CPU clock: -1/+3 clock cycles over the whole range(!).
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Accuracy on 16 MHz CPU clock: delay is about 0.8% too short.
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Exceptions are delays of 0..2 on 20 MHz, which are all 0.75 us and delays
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of 0..3 on 16 MHz, which are all 0.93us.
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*/
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void delay_us(uint16_t delay) {
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// Compensate call overhead, as close as possible.
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#define OVERHEAD_CALL_CLOCKS 39 // clock cycles
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#define OVERHEAD_CALL_DIV ((OVERHEAD_CALL_CLOCKS / (F_CPU / 1000000)) + 1)
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#define OVERHEAD_CALL_REM ((OVERHEAD_CALL_DIV * (F_CPU / 1000000)) - \
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OVERHEAD_CALL_CLOCKS)
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if (delay > OVERHEAD_CALL_DIV) {
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delay -= OVERHEAD_CALL_DIV;
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if (OVERHEAD_CALL_REM >= 2)
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_delay_loop_2((OVERHEAD_CALL_REM + 2) / 4);
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}
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else {
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return;
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}
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while (delay > (65536L / (F_CPU / 4000000L))) {
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#define OVERHEAD_LOOP_CLOCKS 13
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_delay_loop_2(65536 - (OVERHEAD_LOOP_CLOCKS + 2) / 4);
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delay -= (65536L / (F_CPU / 4000000L));
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}
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if (delay)
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_delay_loop_2(delay * (F_CPU / 4000000L));
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}
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#endif /* defined TEACUP_C_INCLUDE && defined __AVR__ */
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