Cypress CE225786 User manual

CE225786 – PSoC 6 MCU: USB Audio
Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 1
Objective
This example demonstrates the use of PSoC®6 MCU to implement an audio recorder using the USB Audio Device Class.
Requirements
Tool: ModusToolbox™ IDE 1.0
Programming Language: C
Associated Parts: All PSoC 6 MCU parts with USB
Related Hardware: PSoC 6 Wi-Fi-BT Pioneer Kit, PSoC 6 Wi-Fi-BT Proto Board
Overview
This code example shows how to stream audio data to a PC over USB using a PSoC 6 device. It uses digital microphones with
the pulse-density modulation (PDM) to pulse-code modulation (PCM) converter hardware block. All the audio data captured by
the microphones are streamed over USB Full-Speed (USBFS) using the Audio Device Class. An audio recorder software tool,
such as Audacity, running on a PC initiates the streaming of audio data.
Figure 1 shows the high level-block diagram of this application.
Figure 1. Block Diagram
PSoC 6 USB Audio Recorder
Arm® Cortex® -
M4 MCU
PDM/PCM USBFS
2
Digital
Microphones Computer
The PDM/PCM interface requires two wires –PDM Clock and PDM Data. Up to two digital PDM microphones can share the
same PDM data line. One microphone samples in the falling edge and the other in the rising edge.
This code example uses FreeRTOS. Visit the FreeRTOS website for documentation and API references of FreeRTOS.
Hardware Setup
This example does not require any additional hardware to run.
Note: The PSoC 6 WiFi-BT Pioneer kit ships with KitProg2 installed. ModusToolbox only works with KitProg3. Before using this
code example, make sure that the kit is upgraded to KitProg3. See ModusToolbox Help > ModusToolbox IDE Documentation
> User Guide, Section PSoC 6 MCU KitProg Firmware Loader. If you do not upgrade, you will see an error like “unable to find
CMSIS-DAP device” or “KitProg firmware is out of date”.
Operation
1. Connect the kit board to your PC using the provided USB cable through the USB connector.
2. Import the application projects into a new workspace or an existing one. See KBA225201.
3. Program the PSoC 6 MCU device. In the project explorer, select the mainapp project. In the Quick Panel, scroll to the
Launches section and click Program (KitProg3) configuration.
4. Connect another USB cable (or reuse the same cable used to program the kit) to the USB Device connector [J28 for
CY8CKIT-062-WiFi-BT and J10 for CY8CPROTO-062-4343W].
5. In the PC, verify that a new USB device was enumerated as a Microphone and named as “PSoC 6 USB Audio Recorder”.

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 2
6. Open an audio recorder software tool in the PC. If you do not have one, download the open-source software Audacity.
Make sure to select the correct microphone in the software tool.
7. Start a recording session. Play a sound, or speak over the microphones in the kit.
8. Stop the recording session and play it to confirm that the audio was recorded correctly.
Debugging
You can debug the example to step through the code. Use a Program+Debug configuration. See KBA224621 in the Cypress
community to learn how to start a debug session with ModusToolbox IDE.
Design and Implementation
The PDM-to-PCM hardware block can sample one or two PDM digital microphones. In this application, the hardware block is
configured to sample stereo audio at 48 ksps with 16-bit resolution. The sample audio data is eventually transferred to the USB
data endpoint buffer. Figure 2 shows the overall transfers performed by the application.
Figure 2. Overall Transfers
PDM/PCM
RX FIFO
SRAM
PCM
Buffer
USB Data
Endpoint
Buffer
DMA
Transfers DMA
Transfers
The first DMA transfer reads from the PDM/PCM RX FIFO and writes to a buffer in the SRAM. This buffer is populated with 16-
bit interleaved data (left and right channels). The second DMA transfer reads from this bufferand writes to the USB Data Endpoint
buffer. The second DMA transfer is handled automatically by the USBFS driver, while the first DMA transfer is part of the
application layer.
The USB descriptor implements the Audio Device Class with three endpoints:
▪Audio Control Endpoint: controls the access to the audio streams
▪Audio IN Endpoint: sends data to the USB host
▪Audio OUT Endpoint: receives data from the USB host (not used in this application)
Only the first two endpoints are used in this application; however, all the hooks in the firmware are placed to enable the Audio
OUT Endpoint. Figure 3 shows the flowchart on how the PDM/PCM data is streamed over USB.

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 3
Figure 3. PDM/PCM to USB Flowchart
Task While Loop
Wait for
Recording
Request
Clear
PDM/PCM
FIFO
Enable
PDM/PCM
Sampling
Write to the
Audio IN
Endpoint Buffer
Audio IN Endpoint Callback
Read PDM/PCM
FIFO Level
Is level too
high?
Is level too
low?
Increase
Frame Size
Decrease
Frame Size
Set Original
Frame Size Enable the DMA PCM Transfer
DMA PCM Interrupt Handler
Is still
streaming?
Disable
PDM/PCM
Sampling
Write to the
Audio IN
Endpoint Buffer
This callback is
executed after
transferring data to
the USB host
This interrupt service routine is
executed after the DMA PCM transfers
one frame data from the PDM/PCM
FIFO to SRAM
Yes
No
Yes
No
No Yes
The audio in ‘task while’ loop waits for a recording request from the USB host. When it receives the request, it prepares the
PDM/PCM block to sample a new frame. It initially writes a null frame to the Audio IN Endpoint buffer to initiate the streaming.
The frame size depends on the sample rate (48 ksps), the number of channels (2x) and the time of USB transfers (1 ms). The
overall equation is:
𝐹𝑟𝑎𝑚𝑒 𝑠𝑖𝑧𝑒 = 𝑆𝑎𝑚𝑝𝑙𝑒 𝑅𝑎𝑡𝑒 × 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝐶ℎ𝑎𝑛𝑛𝑒𝑙𝑠 × 𝑇𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑇𝑖𝑚𝑒
In this example, the frame size is equal to 48000 × 2 x 0.001 = 96 samples. Note that the Audio IN Endpoint Callback also
implements a method to change the frame size depending on the FIFO level in the PDM/PCM block. This is important because
there are clocking differences between the USB host bus and the PSoC 6 MCU audio subsystem.
The DMA PCM is configured to transfer an entire audio frame per trigger. It triggers when there is enough data in the PDM/PCM
FIFO. Once it completes a transfer, it disables itself; it is enabled again only when the Audio IN Endpoint Callback is executed.
On completion, the DMA PCM Interrupt Handler is executed, which might terminate the recording by disabling the PDM/PCM
block or keep the streaming by writing more data to the Audio IN Endpoint buffer.
The firmware uses FreeRTOS to execute the processes required by this application. All tasks run in the Arm® Cortex®-M4 CPU.
The following tasks are created:
1. AudioInTask: described in Figure 3 as the Task While Loop
2. AudioAppTask: initiates the application and handles certain USB events. In this application, no USB events are handled
in this task.
3. DebugTask: handles messages printed to the terminal over UART (optional).
The example also uses the Event Group. It is used to notify tasks when USB events occur. Only the event that initiates a
recording is used in this application.
The project consists of the following files:
▪main.c (CM4) contains the main function, which is the entry point and execution of the firmware application. The main
function sets up user tasks and then starts the RTOS scheduler. The CM0+ equivalent contains the main function that starts
up CM4. CM0+ is not used to run any application code.
▪audio_app.c/h files contain the task that initializes the audio-related blocks, such as the USB and the PDM/PCM blocks,
and handles USB events in the task main loop.
▪audio_in.c/h files contain the task that handle recording requests to the Audio IN endpoint. These files also implement the
Audio IN Data Endpoint callback and the DMA interrupt service routine.

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 4
▪usb_comm.c/h files contain all macros and functions related to the USBFS and USB Audio Device Class.
▪uart_debug.c/h and stdio_user.c/h files are used for retargeting I/O functions such as printf via UARTto a terminal emulation
program.
▪FreeRTOSConfig.h contains the FreeRTOS settings and configuration. Non-default settings are marked with inline
comments. For details of FreeRTOS configuration options, see the FreeRTOS customization webpage.
Resources and Settings
Table 1 lists the ModusToolbox resources used in this example, and how they are used in the design. For pin usage and
configuration, open the Pins tab of the design.modus file.
Table 1: ModusToolbox Resources
Resource
Alias
Purpose
PDM/PCM
KIT_PDM
Connects to the digital microphones.
UART (SCB)
KIT_UART
Debug interface.
USBFS
USBFS
Implements the Audio Device Class.
DMA DataWire
DMA_PCM
Transfers data from PDM/PCM FIFO
to SRAM.
Figure 5 shows the configuration settings for KIT_PDM.
Figure 4. KIT_PDM Configuration
Figure 5 shows the configuration settings for the USBFS block. To visualize the USBFS descriptor, click in the Launch USB
Configuration button from Figure 5. You can also refer to the cycfg_usbdev.h file in the Generated Source folder.

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 5
Figure 5. USBFS Configuration

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 6
Error! Not a valid bookmark self-reference. shows the configuration settings for DMA_PCM.
Figure 6. DMA_PCM Configuration
Figure 8 and Figure 8 show the platform system clock configuration. Note that the FLL and PLL are used in this application.
The FLL is used to clock the CPUs and the USB block. The PLL is used to clock the audio subsystem.
Figure 7. FLL Configuration

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 7
Figure 8. PLL Configuration
Figure 9 shows the high-frequency clock settings.
Figure 9. High-Frequency Clocks Configuration
KIT_UART uses the default configuration for UART.
The following middleware libraries are used in this project:
▪FreeRTOS v10.0.1
▪Retarget I/O
▪USB Device
If you want to explore middleware, right-click the CE225786_mainapp folder in the project explorer window and select
ModusToolbox Middleware Selector.

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 8
Reusing This Example
This example is designed for the CY8CPROTO-062-4343W kit. To port the design to a different PSoC 6 MCU device, right-click
an application project and choose Change ModusToolbox Device. Depending on the device chosen, you might need to
redefine the DMA configuration forthe PDM/PCM DMA (DMA_PCM). Refer to Figure 6 to re-create the DMA_PCM configuration
for the new device.
In some cases, a resource used by a code example (for example, an IP block) is not supported on another device. In that case,
the example will not work. If you build the code targeted at such a device, you will get errors. See the device datasheet for
information on what a particular device supports.
Related Documents
Application Notes
AN221774 –Getting Started with PSoC 6 MCU
Describes the PSoC 6 MCU devices and how to build your first PSoC project
AN215656 –PSoC 6 MCU Dual-Core CPU System
Design
Describes the dual-CPU architecture in the PSoC 6 MCU, and shows how to build a
simple dual-CPU design
Code Examples
Visit the Cypress GitHub site for a comprehensive collection of code examples using ModusToolbox IDE
Device Documentation
PSoC 6 MCU Datasheets
PSoC 6 MCU Technical Reference Manuals
Development Kit Documentation
CY8CKIT-062-WiFi-BT PSoC 6 WiFi-BT Pioneer Kit
CY8CPROTO-062-4343W PSoC 6 Wi-Fi BT Prototyping Kit
Tool Documentation
ModusToolbox IDE
ModusToolbox IDE simplifies development for IoT designers. It delivers easy-to-use tools and a familiar
microcontroller (MCU) integrated development environment (IDE) for Windows, macOS, and Linux.
Cypress Resources
Cypress provides a wealth of data at www.cypress.com to help you to select the rightdevice,and quickly and effectively integrate
the device into your design.
For PSoC 6 MCU devices, see KBA223067 in the Cypress community for a comprehensive list of PSoC 6 MCU resources.

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 9
Document History
Document Title: CE225786 –PSoC 6 MCU: USB Audio Recorder
Document Number: 002-25786
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
6410738
RLOS
12/03/2018
New code example

PSoC 6 MCU: USB Audio Recorder
www.cypress.com Document Number: 002-25786 Rev. ** 10
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