994 audioplayback
994 : audioplayback
- Author: harvin iriawan
- Description: QSPI Flash Audio Playback Controller with 8-bit PCM PWM output
- GitHub repository
- Open in 3D viewer
- Open in Tiny Tapeout Explorer
- Clock: 50000 Hz
How it works
This project is a digital audio playback controller that streams 8-bit PCM audio samples from an external QSPI Flash memory (such as a W25Qxx series chip) and outputs them using a Pulse Width Modulation (PWM) audio driver.
- QSPI Flash Controller (
EF_QSPI_XIP_CTRL):- Initialization: On reset, the controller executes a software reset sequence (
0x66,0x99) to ensure the flash is in standard 1-bit SPI mode. - Data Fetching: It uses the Fast Read Quad I/O (
0xEB) instruction to fetch audio data in 8-byte (64-bit) chunks.
- Initialization: On reset, the controller executes a software reset sequence (
- Playback Buffer & Controller (
playback_ctrl):- The fetched 16 bytes of data are loaded into a buffer.
- Based on the speed control inputs, the buffer plays back the 8-bit PCM samples sequentially and triggers the QSPI controller to fetch the next line once the buffer is depleted.
- Speed Control (
ui_in[1:0]):00$\rightarrow$ 0.5x speed (repeats each sample twice).01$\rightarrow$ 1x speed (normal playback).10$\rightarrow$ 1.5x speed (alternates between playing sample normally and skipping every 2nd sample).11$\rightarrow$ 2x speed (skips every other sample).
- Audio Output (
pwm):- The 8-bit PCM samples are sent to a high-frequency PWM generator.
- The PWM output is driven onto the dedicated output pin
uo_out[7]and bidirectional pinuio_out[7].
How to test
1. Simulation Testing
You can run the provided Cocotb test bench locally using make in the test/ directory. The test simulates:
- An external QSPI flash loaded with a sawtooth audio waveform.
- Real-time playback speed variations and assertion checks on read request generations.
2. Physical Hardware Testing
- Program an external QSPI flash memory chip with raw 8-bit PCM audio data (uncompressed audio samples).
- Wire up the QSPI Flash to the bidirectional IO pins of the Tiny Tapeout board (see Pinout below).
- Select the desired playback speed using the
ui_in[1:0]inputs:ui_in[1:0] = 2'b01for normal speed.
- Apply a system clock (up to 50 MHz).
- Capture or listen to the output at
uo_out[7]oruio_out[7]. Since the output is digital PWM, pass the signal through a low-pass filter (see External Hardware) before feeding it to an audio amplifier or speaker.
External hardware
List external hardware used in your project (see Tiny Tapeout Pinout Specs)
- QSPI Flash
- TT Audio Pmod
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | playback_speed[0] | flash_cs_n | |
| 1 | playback_speed[1] | flash_sd0 | |
| 2 | flash_sd1 | ||
| 3 | flash_sck | ||
| 4 | flash_sd2 | ||
| 5 | flash_sd3 | ||
| 6 | |||
| 7 | pwm_out | audio_out |