added example: atmega2560/atmega2560-servo.rs

examples/arduino-mega2560/src/bin/mega2560-servo.rs

@@ -0,0 +1,112 @@
+//! This example demonstrates how to use the MCU's internal timer/counters
+//! to move a servo motor.
+//!
+//! NOTE: using timer/counters will not put any load to the CPU, but will limit the amount of
+//! servo's you can control with a single board.
+//!
+//! # Servo control
+//!
+//! * 20 ms PWM period required = 50 Hz
+//! * Control range: 0.5 to 2.5 ms for a 0 to 180 degrees rotation.
+//!
+//! If we use the standard simple_pwm, we'll use an 8-bit TC. That would limit us to 256 steps.
+//! The timer/counter will then count from 0 to 255 at the pace defined by the clock (with prescaler
+//! modification). With this we can check which PWM period we can achieve with an 8-bit timer/counter:
+//! * With Prescale64: 1 clock tick of 256 total ticks = 4 us * 256 = +- 1 ms.
+//! * With Prescale256: 1 clock tick = 16us * 256 = 4.1 ms.
+//! * With Prescale1024: 1 clock tick = +- 0.1 us * 256 = 16.4 ms.
+//!
+//! If we use 16-bit timer/counters, we get a better control on the exact PWM period time.
+//! The longest PWM cycle per prescaler is defined by MAX value (2^16) = 65536 (<-> 2^8 = 256).
+//! Options:
+//!     * Prescale8: 16 MHz / 8 = 2 MHz => 0.5 us per clock tick * 65 5363 = 32.8 ms period max.
+//!         --> 20 ms is achieved after 39 999 clock ticks.
+//!     * Prescale64: 16 MHz / 64 = 250 Khz => 4us per clock tick * 65 536 = 262 ms perios max.
+//!         --> 20 ms is achieved after 4 999 clock ticks.
+//! This gives the following possible resolutions:
+//! * Prescale8: 0.5 ms - 2.5 ms = 2 ms control range = 4000 clock ticks => 0.045 degrees per step.
+//! * Prescale64: 0.5 - 2.5 ms = 500 clock ticks => 0.36 degrees per step.
+//!
+//! For most cases Prescale64 will be sufficient.
+//!
+//! Note: On the ATMega2560 TC1, TC3, TC4 and TC5 are 16-bit timer/counters.
+//!       TC0 and TC2 are 0-bit timer/counters.
+//!
+//! For details on the timer/counter registers, refer to the Arduino-Mega docs: https://docs.arduino.cc/hardware/mega-2560/
+
+#![no_std]
+#![no_main]
+
+use panic_halt as _;
+
+#[arduino_hal::entry]
+fn main() -> ! {
+    let dp = arduino_hal::Peripherals::take().unwrap();
+    let pins = arduino_hal::pins!(dp);
+
+    // Take Timer/Counter3 (TC3) from Peripherals
+    let tc3 = dp.TC3;
+    // Reset all TC3 registers A, B and C. These registers define the behaviour of the TC.
+    tc3.tccr3a().reset();
+    tc3.tccr3b().reset();
+    tc3.tccr3c().reset();
+
+    // // Compare mode set-up in register TCCR1A
+    // // - bits 7:6 - COM1A1:0 = Output compare mode for OC1A (for channel A)
+    // // - bits 5:4 - COM1B1:0 = Output compare mode for OC1B (for channel B)
+    // // - bits 3:2 - COM1C1:0 = Output compare mode for OC1C (for channel C)
+    // Here will use pin D3, which is port PE5. PE5 uses TC3 with output compare channel A.
+
+    // Wave generation mode 14: WGM bits 0:3 1110 => FastPWM with ICRn to define TOP and OCRNX to define compare output.
+    // WGM bits 0:1 go into TCCR3A (0b10)
+    // WGM bits 2:3 go into TCCR3B (0b11)
+
+    tc3 // In TC3
+        .tccr3a() // Access register TCCR3A (TCCnx in the datasheet)
+        .write(
+            |w| unsafe {
+                // write to the register. This is unsafe as there's no protection against concurrent writing.
+                w // Writer wrapper
+                    .com3a()
+                    .bits(0b10) // Write bits 0b10 to the com3a bits in register TCCR3A
+                    .wgm3()
+                    .bits(0b10)
+            }, // Write WGM bits 2:3 into
+        );
+    // Same operation for TCCR3B.
+    tc3.tccr3b().write(
+        |w| unsafe {
+            w.wgm3()
+                .bits(0b11) // Set WGM bits 2:3
+                .cs3()
+                .prescale_64()
+        }, // Set clock select bits. Using the avr-hal pre-defined prescale bits.
+    );
+    // We don't need TCCR3C for the servo.
+
+    // TOP will define the length of the total PWM cycle.
+    // Setting IRC3 to 4999 (now TOP for this TC) to achieve 50 Hz cycle.
+    // IMPORTANT: This affects all channels (A, B and C) of Timer/Counter3!
+    tc3.icr3().write(|w| w.set(4999u16));
+
+    // Setting duty cycle on channel C using OCR3A. When the TC3 count register hits this value,
+    // Output Compare 3 will be toggled. It will invert the pin from high to low (due to how we set the COM3A bits)
+    // * 0.5 ms = 125 ticks (0 - 124)
+    // * 2.0 ms = 500 ticks (0 - 499)
+    // * 2.5 ms = 625 ticks (0 - 624)
+    // Servo SG90 0 degrees = 0.5 ms -> with Prescale8 = 124
+    // Servo SG90 180 degrees = 2.5 ms -> with Prescale8 = 624
+    tc3.ocr3a().write(|w| w.set(124u16)); // Now we set it to 0 degrees.
+
+    // Toggle pin D3 into an output pin connect it to the TC3 output.
+    // Connect your servo with its PWM pin to your board's D3 pin.
+    // VCC to 5V and GND to GND offcourse.
+    pins.d3.into_output();
+
+    loop {
+        for ticks in [124u16, 374u16, 624u16, 374u16] {
+            tc3.ocr3a().write(|w| w.set(ticks)); // Now we set the angle using the 'duty'.
+            arduino_hal::delay_ms(500);
+        }
+    }
+}