1. USBasp programmer

  • You can use your AD2 with Waveforms as an AVR ISP programmer.

1.1. OSX

Instructions for Mac OSX, including avr-gcc and avrdude: https://bytes.usc.edu/ee109/macos-64-bit-toolchain/

1.2. Windows 10

Windows 10 apparently needs a USB driver for things to work properly.

  • Download zadig-2.7.exe from https://zadig.akeo.ie/

  • Run the program (as an Admin) and select the libusbK driver.

  • Then, when using avrdude, use the following options:+

    • avrdude -P usb -c usbasp
      (and other options for your particular target, -p m128ra1a or -p attiny85)

    • -U flash:w:filename.hex:i is the option to program the flash from your HEX file.

zadig usbasp libusbk

1.3. USBasp dongle notes

USBasp - USB programmer for Atmel AVR controllers — the original design.

  • JP2:
    The clone versions we have add a 3.3 V voltage regulator to power the target at: 5 V, or 3.3 V, or none (target provides its own power).

    • Use the none option when programming your SRXE.

  • Shorting JP1 connects the RST pin on the programming header to the programmer’s ATmega8. This lets you re-program the programmer with new firmware.

I have done this connection and dumped the firmware on the programmers that we have. The firmware currently on them is an exact match to the usbasp.atmega8.2011-05-28.hex, which is the latest version of USBasp. Therefore no need to actually update the firmware on our units.

2. Porting ShortSquawker to an RTOS

  • Figure out the the original version!

  • Convert to tasks that operate independently of each other. Maybe add some communication between each task.

FreeRTOS documentation

[handout of the ISR code]

The Entire runtime is tick()'d by the TIMER0_COMPA interrupt which happens at 10 kHz or every 100 μs. That ISR needs to always finish in less than 100 μs!

  • OCR1A sets the output signal’s duty cycle using the Timer1 hardware connected to the speaker pin.

  • timer_count is a static variable that counts how many times the ISR has run since reset.

    • Difference between static variable inside a function vs. a "global" variable in C.

  • The ADC is handled every ADC_PERIOD ticks, ⇒
    Resulting period / frequency ⇒

  • The input button is handled every INPUT_PERIOD ticks, ⇒
    Resulting period / frequency ⇒

2.1. ISRs and sample rates

General principle: code for an ISR should be as short (time) as possible. It should only handle exactly the parts that need that level of deterministic and precise timing.

Be prepared to justify why you may choose to violate this principle! → Document this decision in the code itself.

Therefore, the Arduino version of ShortSquawker is horrible :(

Output sample rate must be smooth with no timing jitter.

Input sample rate (ADC) should have small timing jitter.

2.2. Improvements

  • Move the sound output ON/OFF decision out of the ADC handling block.

    • Also better handle the alternating tone feature.

  • Use a double-buffer for updating the OCR1A value.

    • DO NOT call signal_synth() from the ISR (why?)

  • Is there a better way to handle user button input detection?

2.3. FreeRTOS API hints

vTaskDelay