3 Implementation

When the program is started, the setup of the external memory and internal peripherals is initiated. This involves the setup of the SPI for data storage device interfacing, ADC for sampling of the microphone, DAC for output to the speaker, PORT settings for buttons, a timer for correct sampling and playback frequency, and event system for signaling the ADC. Separate buttons are set up to trigger the record, playback, and erase subroutines. This functionality is depicted in the figure below.

After the record button is pressed, the routine depicted in the figure below is initiated. The flowchart on the left indicates functionality in software, and the one on the right indicates hardware. ADC is triggered to start a conversion when the sampling timer overflows. An ISR is triggered when the conversion result is ready, which stores the result in a buffer. When the buffer is full, it is sent to the external memory by the software routine (signaling from the ISR to the software routine is made via a globally defined flag). Two alternating buffers are used to avoid loss of data.

When the playback button is pressed, the routine depicted in the figure below is initiated. As stated before, the flowcharts on the left and right reflect functionality in software and hardware, respectively. The sample timer overflow ISR updates the DAC data register in order to change the output at the same rate as the samples were taken. This results in a reconstructed signal, which is as accurate as possible.

When the erase button is pressed, the routine depicted in the figure below is initiated. This routine erases the external memory between the start of memory and the last write location.