Merge pull request #28 from emeb/master

Added README files to some examples

examples/adc_polled/README.md

+# Polled ADC example
+This example code demonstrates the use of the CH32V003 on-chip ADC in polled mode
+wherein a single analog input channel is configured on GPIO and then digitized
+under software control. When a sample is needed the ADC is started and the CPU
+busy-waits until the conversion is complete before reading the result.
+
+This is just about the simplest and easiest use-case for the ADC and wastes a lot
+of CPU cycles but it does show the basics of doing conversions in a situation
+where high performance is not needed.
+
+## Use
+Connect an analog voltage source that varies between 0V and 3.3v to GPIO pin PD4
+and a 3.3V logic level serial terminal to pin PD5. The 10-bit result will be
+printed periodically on the serial output.

examples/i2c_oled/README.md

+# I2C OLED demonstration
+This example code demonstrates use of the CH32V003 I2C peripheral with an SSD1306
+OLED (128x32 pixel type). It provides a generic I2C port initialization and
+transmit (write-only) low level interface and a high-level graphics driver with
+pixels, lines, circles, rectangles and 8x8 character font rendering. Out of the
+box this demo cycles through a few different graphic screens to test out the
+various drawing primitives.
+
+
+https://user-images.githubusercontent.com/1132011/230734071-dee305de-5aad-4ca0-a422-5fb31d2bb0e0.mp4
+
+
+## Use
+Connect an SSD1306-based OLED in I2C interface mode to pins PC1 (SCL) and PC2 (SDA)
+of the CH32V003 with proper I2C pullup resistors and observe the various graphic
+images that cycle at approximately 2 second intervals.
+
+Note - I used an Adafruit 0.91" 128x32 OLED breakout (stock #4440) for my testing
+and found that the built-in 10k pullup resistors were too weak for reliable I2C
+bus transactions. I had to add 2.2k resistors to the SCL and SDA pads to allow
+proper operation.
+

examples/systick_irq/README.md

+# Systick IRQ demonstration
+This example shows how to set up the built-in Systick IRQ to generate periodic
+interrupts for timing. Many bare-metal and RTOS based embedded applications will
+use the Systick IRQ for timing, periodic housekeeping and task arbitration so
+knowing how to set that up is useful.
+
+Note that this example is *NOT* compatible with the Delay_Ms() function that's
+part of the ch32v003fun library - that function uses the Systick counter for
+doing busy-wait delays and will interfere with its use in generating predictable
+IRQs. Do not use the built-in Delay_Ms() and related functions when using Systick
+for IRQs.
+
+Note also the use of the  `__attribute__((interrupt))` syntax in declaring the
+IRQ handler. Some of the IRQ examples from the WCH HAL library have slightly
+different syntax to make use of a fast IRQ mode but which is not compatible with
+generic RISC-V GCC so that feature is not used here.
+
+# Use
+Connect LEDs (with proper current limit resistors) to GPIO pins C0, D0, D4 and
+a 3.3V logic level serial terminal to PD5. The LEDs will flash and an incrementing
+count will be printed to the serial port at rates that are controlled by the
+Systick IRQ.

examples/tim1_pwm/.gdbinit

+file tim1_pwm.elf
+target extended-remote localhost:3333

examples/tim1_pwm/README.md

+# Demonstration of PWM using Timer 1
+This example shows how to set up Timer 1 (the Advanced Control Timer) to generate
+Pulse-Width Modulation (PWM) on two output pins. PWM is frequently used to do
+variable brightness on LEDs or for digital-to-analog conversion when combined with
+a suitable lowpass filter.
+
+## Use
+Connect GPIO pins PD0 and PC4 to LEDs (with appropriate current limiting) and
+observe that they fade with different cycles.

examples/tim1_pwm/debug.sh

+#!/bin/bash
+# before running this you should start OOCD server
+#../../../MRS_Toolchain_Linux_x64_V1.70/OpenOCD/bin/openocd -f ../../../MRS_Toolchain_Linux_x64_V1.70/OpenOCD/bin/wch-riscv.cfg
+ 
+../../../MRS_Toolchain_Linux_x64_V1.70/RISC-V\ Embedded\ GCC/bin/riscv-none-embed-gdb