FreeRTOS Configuration

Could all this not be done just using a timer? Or is that what an RTOS essential is?

 * Task 1:
 * - executes at a frequency of 1 quarter note
 * - updates tempo / timer to match external clock
 * 
 * Task 2:
 * - executes at a frequency of PPQN
 * - advances the sequencer
 * - handles any interface changes (ie. touch, bend, UI buttons)
 * - updates LEDs
 * - updates DACs
 * 
 * Task 3:
 * - executes at a frequency of PPQN * 8? 🤷‍♂️
 * - reads and filters ADCs
 * 
 * Task 4:
 * - low priority for printf()
 * 
 * State Struct:
 * - is shared globally between tasks
 * - holds a series of "flags" for which to tell each task which code it should execute
 * 
 * Software Timers:
    - this is what MBED must have used to create timed events. 
    - if the RTOS is clocked by the sequencer clock, this could be very usefull
 * 

Toolchain

Install OpenOCD for ST-Link Debugging

brew install openocd

Install ARM Embedded Toolchain

# not sure about the brew tap, but it works.
brew tap PX4/homebrew-px4
brew update
brew install gcc-arm-none-eabi
arm-none-eabi-gcc --version

Pull submodules

git submodule init
git submodule update

Making changed to git submodules

First, cd into the submodule directory and checkout a new branch with git checkout -b myBranchName

You can now commit changes and push to the remote

Bootloader

No external pull-up resistor is required

Bootloader ID: 0x90

Memory location: 0x1FFF76DE

Install dfu-util

brew install dfu-util

To enter bootloader mode, hold down BOOT, then, hold down RESET. Release RESET button (before releasing BOOT)

Run dfu-util -l and you should see the following output:

dfu-util 0.11

Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2021 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/

Found DFU: [0483:df11] ver=2200, devnum=2, cfg=1, intf=0, path="64-1.2", alt=3, name="@Device Feature/0xFFFF0000/01*004 e", serial="STM32FxSTM32"
Found DFU: [0483:df11] ver=2200, devnum=2, cfg=1, intf=0, path="64-1.2", alt=2, name="@OTP Memory /0x1FFF7800/01*512 e,01*016 e", serial="STM32FxSTM32"
Found DFU: [0483:df11] ver=2200, devnum=2, cfg=1, intf=0, path="64-1.2", alt=1, name="@Option Bytes  /0x1FFFC000/01*016 e", serial="STM32FxSTM32"
Found DFU: [0483:df11] ver=2200, devnum=2, cfg=1, intf=0, path="64-1.2", alt=0, name="@Internal Flash  /0x08000000/04*016Kg,01*064Kg,03*128Kg", serial="STM32FxSTM32"

Using dfuse-pack.py (not yet tested)

This file was pulled from the dfu-util repo, and is meant to convert .hex files into .dfu files. Note: Make sure you have the IntelHex python module installed.

Using a .bin file (tested and working)

dfu-util -a 0 -s 0x08000000:leave -D ./path/to/file.bin

FreeRTOS

Task States

Suspended:

• will not execute

READY:

• A task in the ready state can move to the running state. It is not executing, it is waiting for the scheduler to execute it
• there is no function which moves a task from READY to RUNNING, the task scheduler does all of that.

RUNNING:

Task has the processor, and is currently executing its while loop

BLOCK:

• When a task is waiting for a particular event to occur such as a semephor or a delay
• task must move to ready state before it can be put back into a running state

TaskHandle_t A struct which holds the configuration / access to a specific task. Used as an argument when modifying a task.

• vTaskSuspend() Suspend a Task
• vTaskResume()
• vTaskPrioritySet() Set the priority of a task at run-time
• vTaskDelayUntil() use this to execute a thread periodically / at a set frequency

Idle Hook Function

Use this task to execute clean up code

Tick Hook

Function that is called by the kernel during each tick interupt. You are best off not even using it as it could / will cause jitter in your RTOS system

extern void vApplicationStackOverflowHook(xTaskHandle *pxTask, signed portCHAR *pcTaskName);

If the function is defined, FreeRTOS will invoke it when it detects that it has overrun a stack limit. This allows the application designer to decide what should be done about it. You might, for example, want to flash a special red LED to indicate program failure.

Queues

Queues are used as FIFO buffers, where data is inserted at the back and removed from the front. You can insert data into the queue by passing values or references (pointers), the latter being the most optimal for speed and large data

A task can be placed in a blocked state in order to wait for data to be available from the queue - as soon as data is available the task is automatically moved into the ready state.

Task can be placed in a blocked state if queue is full, and as soon as the space becomes available the queue task is moved to the ready state.

Uses: transfer data from one stask to another, or a task to an ISR, or an ISR to a task.

Common Queue APIs -> xQueueSend(), xQueueSendToFront(), xQueueSendToBack()

Queuesets

Allow a task to recieve data from more than one queue without the task polling each queue in turn to determine which, if any, contains data

Terminating a Task

By default, the functions required to do this are not enabled and need to be configured in FreeRTOSConfig.h

GCC Reference:

The __attribute((unused)) is a gcc attribute to indicate to the compiler that the argument args is unused, and it prevents warnings about it.

Preventing compiler optimazation for debugging

Use this __attribute__((optimize("O0"))) to disable optimizations for a function. ex.

void __attribute__((optimize("O0"))) myFunc()
{
    // this will not be optimized
}

DEV TOOLS:

• Bitwise Operations Playground