Add LED Fade Example

An example that uses ULP self-modifying code to create a PWM-like LED dimming effect on GPIO 15.

Author: mjaspers2mtu

examples/fade_s2.py

@@ -0,0 +1,82 @@
+#
+# This file is part of the micropython-esp32-ulp project,
+# https://github.com/micropython/micropython-esp32-ulp
+#
+# SPDX-FileCopyrightText: 2018-2023, the micropython-esp32-ulp authors, see AUTHORS file.
+# SPDX-License-Identifier: MIT
+
+"""
+Example for: ESP32-S2 Wemos mini development board V1.0.0 with led on pin 15
+
+This example creates a PWM-like dimming effect using self-modifying ULP code.
+The ULP program rewrites the `WAIT` instructions to control on/off LED durations,
+simulating a variable duty cycle.
+
+Note:
+The `WAIT` instruction uses an immediate operand (fixed value) for delay cycles. However, we can change the lower half of memory
+to modify these values at runtime, simulating variable wait times via registers.
+"""
+
+from esp32 import ULP
+from machine import mem32
+from esp32_ulp import src_to_binary
+from time import sleep
+
+source = """\
+# constants from:
+# https://github.com/espressif/esp-idf/blob/v5.0.2/components/soc/esp32s2/include/soc/reg_base.h
+#define DR_REG_RTCIO_BASE            0x3f408400
+
+# constants from:
+# https://github.com/espressif/esp-idf/blob/v5.0.2/components/soc/esp32s2/include/soc/rtc_io_reg.h
+#define RTC_IO_XTAL_32P_PAD_REG      (DR_REG_RTCIO_BASE + 0xC0)
+#define RTC_IO_X32P_MUX_SEL_M        (BIT(19))
+#define RTC_GPIO_OUT_REG             (DR_REG_RTCIO_BASE + 0x0)
+#define RTC_GPIO_ENABLE_REG          (DR_REG_RTCIO_BASE + 0xc)
+#define RTC_GPIO_ENABLE_S            10
+#define RTC_GPIO_OUT_DATA_S          10
+
+# constants from:
+# https://github.com/espressif/esp-idf/blob/v5.0.2/components/soc/esp32s2/include/soc/rtc_io_channel.h
+#define RTCIO_GPIO15_CHANNEL         15
+
+.global entry
+program_init:
+            # connect GPIO to ULP (0: GPIO connected to digital GPIO module, 1: GPIO connected to analog RTC module)
+            WRITE_RTC_REG(RTC_IO_XTAL_32P_PAD_REG, RTC_IO_X32P_MUX_SEL_M, 1, 1);
+
+            # enable GPIO as output, not input (this also enables a pull-down by default)
+            WRITE_RTC_REG(RTC_GPIO_ENABLE_REG, RTC_GPIO_ENABLE_S + RTCIO_GPIO15_CHANNEL, 1, 1)
+
+set_waits:  add r0, r0, 0xFF # Increase r0 (delay time)
+            move r3, wait_off
+            st r0, r3, 0 # Overwrite wait_off with new delay value
+            
+            move r2, 0xFFFF
+            sub r1, r2, r0 # Calculate complementary delay time     
+            move r3, wait_on
+            st r1, r3, 0 # Overwrite wait_on with new value
+
+            WRITE_RTC_REG(RTC_GPIO_OUT_REG, RTC_GPIO_OUT_DATA_S + RTCIO_GPIO15_CHANNEL, 1, 0) # turn off led
+wait_off:   wait 0 # Placeholder; value overwritten dynamically
+            WRITE_RTC_REG(RTC_GPIO_OUT_REG, RTC_GPIO_OUT_DATA_S + RTCIO_GPIO15_CHANNEL, 1, 1) # turn on led
+wait_on:    wait 0 # Placeholder; value overwritten dynamically
+  
+jump set_waits # Loop program
+
+"""
+
+binary = src_to_binary(source, cpu="esp32s2")  # cpu is esp32 or esp32s2
+
+load_addr, entry_addr = 0, 0
+
+ULP_MEM_BASE = 0x50000000
+
+ulp = ULP()
+ulp.load_binary(load_addr, binary)
+
+ulp.run(entry_addr)
+
+while True:
+    print(hex(mem32[ULP_MEM_BASE + 40])) # show that the WAIT cycles are changing
+    sleep(0.5)