ELEC60013 Embedded Systems - Music Synthesizer Documentation

The following document outlines the design, implementation and real-time dependecies of a music synthesizer for the 2nd coursework of the Embedded Systems module.

System tasks

The sytem at hand executes several real-time tasks, including: *Reading the key matrix *Updating the display *Generating sound

Reading the key matrix

Purpose: *Decode the key matrix, obtaining the states of the keys, knobs and joysticks *Obtain the currently selected note from the decoded key matrix *Select the appopriate step size for the currently selected note *Transmit the currently selected note, along side its state (pressed or released) using CAN *Obtain any changes in the knobs from the decoded key matrix, corresponding to volume, octave or waveform

Function: code(void scanKeysTask(void *pvParameters)) Implementation: Thread, executing every 50ms Minimum initiation time: TO BE COMPLETED. Maximum execution time: TO BE COMPLETED. Priority: Highest (1), as playing the appropriate sound is more important than updating the display.

Updating the display

Purpose: *Display the currently selected note (string) *Display the current volume (int) *Display the current octave (int) *Display the current waveform (XMB icons)

Function: code(displayUpdateTask(void *pvParameters) Implementation: Thread, executing every 100ms. While a refresh rate of 10Hz does not sound impressive; the display is largely static. Therefore, 100ms was perfectly accetable, without any noticeable delays. Minimum initiation time: TO BE COMPLETED. Maximum execution time: TO BE COMPLETED. Priority: Lowest (2).

Generating the sound

Purpose: *Adds the sample rate to the accumulated value, corresponding to the desired frequency *Sets the output voltage, by using the accumlated value and the desired volume *Writes to analogue output, generating the desired sound

Function: code(sampleISR()) Implementation: Interrupt executing with a frequency of 44.1kHz Minimum initiation time: TO BE COMPLETED. Maximum execution time: TO BE COMPLETED.

CAN

Purpose:

• TO BE ADDED

Function: Implementation: Minimum initiation time: Maximum execution time: Priority:

Critical instant analysis of the rate monotonic scheduler

TO BE ADDED - After system is completed.

CPU Resource Usage

TO BE ADDED - After system is completed; see this link: https://edstem.org/us/courses/19499/discussion/1300057

Shared data structures

Shared data structures: *code(currentStepSize), safe access guaranteed using code(std::atomic<uint32_t>) *code(keyArray), each element within the array is of type code(std::atomic<uint8_t>) *msgInQ, handled by FreeRTOS *code(RX_Message), handled by code(std::atomic_flag)

It was desiced to use C++ code(std::atomic), as it is easier to use and implement, while providing the same functionality as a mutex. According to the documentation: "Each instantiation and full specialization of the std::atomic template defines an atomic type. If one thread writes to an atomic object while another thread reads from it, the behavior is well-defined (see memory model for details on data races). In addition, accesses to atomic objects may establish inter-thread synchronization and order non-atomic memory accesses as specified by std::memory_order." (https://en.cppreference.com/w/cpp/atomic/atomic)

TODO - Expand on the memory model for std:: atomic. TODO - Explain how FreeRTOS handles msgInQ. TODO - Once CAN is completed, expand on the protection of RX_Message

Analysis of inter-task blocking dependencies