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-rw-r--r--platforms/avr/_wait.h38
1 files changed, 29 insertions, 9 deletions
diff --git a/platforms/avr/_wait.h b/platforms/avr/_wait.h
index 683db6ae57..c1a598a428 100644
--- a/platforms/avr/_wait.h
+++ b/platforms/avr/_wait.h
@@ -17,6 +17,26 @@
#include <util/delay.h>
+// http://ww1.microchip.com/downloads/en/devicedoc/atmel-0856-avr-instruction-set-manual.pdf
+// page 22: Table 4-2. Arithmetic and Logic Instructions
+/*
+ for (uint16_t i = times; i > 0; i--) {
+ __builtin_avr_delay_cycles(1);
+ }
+
+ .L3: sbiw r24,0 // loop step 1
+ brne .L4 // loop step 2
+ ret
+ .L4: nop // __builtin_avr_delay_cycles(1);
+ sbiw r24,1 // loop step 3
+ rjmp .L3 // loop step 4
+*/
+
+#define AVR_sbiw_clocks 2
+#define AVR_rjmp_clocks 2
+#define AVR_brne_clocks 2
+#define AVR_WAIT_LOOP_OVERHEAD (AVR_sbiw_clocks + AVR_brne_clocks + AVR_sbiw_clocks + AVR_rjmp_clocks)
+
#define wait_ms(ms) \
do { \
if (__builtin_constant_p(ms)) { \
@@ -27,15 +47,15 @@
} \
} \
} while (0)
-#define wait_us(us) \
- do { \
- if (__builtin_constant_p(us)) { \
- _delay_us(us); \
- } else { \
- for (uint16_t i = us; i > 0; i--) { \
- _delay_us(1); \
- } \
- } \
+#define wait_us(us) \
+ do { \
+ if (__builtin_constant_p(us)) { \
+ _delay_us(us); \
+ } else { \
+ for (uint16_t i = us; i > 0; i--) { \
+ __builtin_avr_delay_cycles((F_CPU / 1000000) - AVR_WAIT_LOOP_OVERHEAD); \
+ } \
+ } \
} while (0)
#define wait_cpuclock(n) __builtin_avr_delay_cycles(n)
#define CPU_CLOCK F_CPU