HARDWARE LAB 18 · PCM / DAC / AUDIO DMA

KEEP THE DAC FED.

Follow an analog tone through sampling, signed PCM codes, a circular DMA buffer, and a zero-order-hold DAC. Then overload the refill path until the buffer runs dry.

PCM FORMAT44.1 kHz · 16-BITBUFFER512 / 512 FRAMESOUTPUT1.00 kHzXRUNS0

SAMPLER + DAC SCOPE

ANALOG → CODES → STAIRS

NYQUIST OK

ANALOG SOURCEQUANTIZED SAMPLEDAC HOLD

CIRCULAR BUFFER LOGIC ANALYZER

OCCUPANCY + DMA EVENTS

STREAMING

BUFFER OCCUPANCY 100%CPU + DMA LOAD 28.0%

BENCH STATE

PRESET + TRANSPORT

PRESET

Comfortable buffer headroom at a matched 44.1 kHz record and playback clock.

SAMPLER + DAC

CONVERSION CLOCKS

PCM SAMPLE RATEBIT DEPTHDAC PLAYBACK CLOCKSOURCE FREQUENCY 1.00 kHz

Nyquist: 22.05 kHz
Folded signal: 1.00 kHz
Ideal SNR: 98.1 dB
1 LSB: 3.05e-5

MEMORY → PERIPHERAL

DMA PRESSURE

CIRCULAR BUFFERCOMPETING CPU LOAD 28%AUTOMATIC DMA REFILL Disable it to let the DAC drain the ring buffer.

Full capacity: 11.61 ms
Headroom now: 11.61 ms
Service latency: 0.61 ms
Requests / refills: 0 / 0

EVENT TRACE

DMA HANDSHAKE

Time	Event	Occupancy	Request
0.00 ms	START	512 / 512	IDLE

ONE CURRENT SAMPLE

CODE → VOLTAGE

ANALOG REQUEST0.00000SIGNED PCM CODE0DAC LEVEL0.00000QUANTIZATION ERROR0.00e+0

The DAC holds each code until the next playback-clock edge. During an underrun, this model holds the last valid code—an audible discontinuity when fresh data resumes.

DATA PATH

WHO DOES WHAT?

01SAMPLERMeasures the source every 1 / sample-rate seconds.
02QUANTIZERRounds each measurement to one signed PCM code.
03MEMORY + DMAMoves bursts into a circular peripheral buffer.
04PLAYBACK CLOCKConsumes one frame per DAC clock edge.
05DAC + HOLDTurns each code into a level until the next code arrives.