Fix blink example by correctly toggling output

The blink example was incorrect (as pointed out in issue #78).

The example was toggling the GPIOs "output enable" state,
instead of keeping "output enable" on and then toggling the
output value of the pin.

It "accidentally" worked, because we initally set the output
value to 1 (high) and thus, whenever "output enable" was set,
the LED lit up, and when "output enable" was turned off, the
pin was left floating without any output voltage and the LED
therefore turned off.

The new approach correctly enables "output enable" at the
start, and then only toggles the output value of the pin on
and off.

This change was also tested with a logic analyser, showing
that before this change, the logic analyser could not correcly
detect a LOW state after a HIGH state, because the pin was
floating without a pull-down resistor in place, whenever it
was not in "output enable" mode.

After this change, the logic analyser correctly detected all
LOW and HIGH states, because the pin remained in "output
enable" mode (and the ESP32 has a pull-down configured by
default) and only the output value was toggled.

Author: wnienhaus

examples/blink.py

@@ -30,10 +30,8 @@
 #define RTC_IO_TOUCH_PAD2_REG        (DR_REG_RTCIO_BASE + 0x9c)
 #define RTC_IO_TOUCH_PAD2_MUX_SEL_M  (BIT(19))
 #define RTC_GPIO_OUT_REG             (DR_REG_RTCIO_BASE + 0x0)
-#define RTC_GPIO_ENABLE_W1TS_REG     (DR_REG_RTCIO_BASE + 0x10)
-#define RTC_GPIO_ENABLE_W1TC_REG     (DR_REG_RTCIO_BASE + 0x14)
-#define RTC_GPIO_ENABLE_W1TS_S       14
-#define RTC_GPIO_ENABLE_W1TC_S       14
+#define RTC_GPIO_ENABLE_REG          (DR_REG_RTCIO_BASE + 0xc)
+#define RTC_GPIO_ENABLE_S            14
 #define RTC_GPIO_OUT_DATA_S          14
 
 # constants from:
@@ -62,8 +60,8 @@
   # connect GPIO to ULP (0: GPIO connected to digital GPIO module, 1: GPIO connected to analog RTC module)
   WRITE_RTC_REG(RTC_IO_TOUCH_PAD2_REG, RTC_IO_TOUCH_PAD2_MUX_SEL_M, 1, 1);
 
-  # GPIO shall be output, not input
-  WRITE_RTC_REG(RTC_GPIO_OUT_REG, RTC_GPIO_OUT_DATA_S + gpio, 1, 1);
+  # GPIO shall be output, not input (this also enables a pull-down by default)
+  WRITE_RTC_REG(RTC_GPIO_ENABLE_REG, RTC_GPIO_ENABLE_S + gpio, 1, 1)
 
   # store that we're done with initialisation
   move r0, magic
@@ -83,12 +81,12 @@
 
 on:
   # turn on led (set GPIO)
-  WRITE_RTC_REG(RTC_GPIO_ENABLE_W1TS_REG, RTC_GPIO_ENABLE_W1TS_S + gpio, 1, 1)
+  WRITE_RTC_REG(RTC_GPIO_OUT_REG, RTC_GPIO_OUT_DATA_S + gpio, 1, 1)
   jump exit
 
 off:
   # turn off led (clear GPIO)
-  WRITE_RTC_REG(RTC_GPIO_ENABLE_W1TC_REG, RTC_GPIO_ENABLE_W1TC_S + gpio, 1, 1)
+  WRITE_RTC_REG(RTC_GPIO_OUT_REG, RTC_GPIO_OUT_DATA_S + gpio, 1, 0)
   jump exit
 
 exit: