esp32: Provide improved version of mp_hal_delay_us_fast.

dpgeorge · dpgeorge · commit 38d94222e0ec · 2017-02-06T14:55:13.000+11:00
This makes software I2C and SPI significantly faster.
diff --git a/esp32/mphalport.c b/esp32/mphalport.c
@@ -93,6 +93,15 @@ void mp_hal_delay_us(uint32_t us) {
     vTaskDelay(us / 1000 / portTICK_PERIOD_MS);
 }
 
+// this function could do with improvements
+void mp_hal_delay_us_fast(uint32_t us) {
+    uint32_t delay = ets_get_cpu_frequency() / 19;
+    while (--us) {
+        for (volatile uint32_t i = delay; i; --i) {
+        }
+    }
+}
+
 /*
 extern int mp_stream_errno;
 int *__errno() {
diff --git a/esp32/mphalport.h b/esp32/mphalport.h
@@ -42,10 +42,10 @@ __attribute__((always_inline)) static inline uint32_t mp_hal_ticks_cpu(void) {
 }
 
 void mp_hal_delay_us(uint32_t);
+void mp_hal_delay_us_fast(uint32_t);
 void mp_hal_set_interrupt_char(int c);
 uint32_t mp_hal_get_cpu_freq(void);
 
-#define mp_hal_delay_us_fast(us) mp_hal_delay_us(us) // TODO
 #define mp_hal_quiet_timing_enter() disable_irq()
 #define mp_hal_quiet_timing_exit(irq_state) enable_irq(irq_state)
 

Original file line number	Diff line number	Diff line change
`@@ -42,10 +42,10 @@ __attribute__((always_inline)) static inline uint32_t mp_hal_ticks_cpu(void) {`
`42`	`42`	`}`
`43`	`43`
`44`	`44`	`void mp_hal_delay_us(uint32_t);`
	`45`	`+void mp_hal_delay_us_fast(uint32_t);`
`45`	`46`	`void mp_hal_set_interrupt_char(int c);`
`46`	`47`	`uint32_t mp_hal_get_cpu_freq(void);`
`47`	`48`
`48`		`-#define mp_hal_delay_us_fast(us) mp_hal_delay_us(us) // TODO`
`49`	`49`	`#define mp_hal_quiet_timing_enter() disable_irq()`
`50`	`50`	`#define mp_hal_quiet_timing_exit(irq_state) enable_irq(irq_state)`
`51`	`51`