EEPROM Dump

With the serial port yielding nothing, I turned to the other accessible memory in the system: the AT24C512 I2C EEPROM at U6, which stores the entire D2Audio DSP firmware.

Identifying the chip

The SOIC-8 package carries Atmel markings: ATMLH007 / 2FCD / CN / 20071YC. The 2FC marking code identifies this as an AT24C512 — a 512Kbit (64KB) I2C serial EEPROM. Date code places manufacture in early 2007, consistent with the amp’s design era. The chip operates at 2.5V to 5.5V with I2C clock speeds up to 1MHz.

The AT24C512’s pinout on this SOIC-8 package:

Pin	Function	Notes
1	A0	Address bit 0 (floats to GND internally)
2	A1	Address bit 1 (floats to GND internally)
3	A2	Address bit 2 (floats to GND internally)
4	GND	Ground
5	SDA	Serial data
6	SCL	Serial clock
7	WP	Write protect (floats to GND = writes enabled)
8	VCC	Power supply

With all address pins at GND, the chip responds at I2C address 0x50.

The read

I used a CH341A USB programmer in I2C mode with an SOIC-8 clip, connected directly to U6 with the amplifier powered off. The CH341 supplies 3.3V to the EEPROM through the clip, keeping the D2-81431 and LPC2103F unpowered to avoid bus contention.

ch341eeprom -v -s 24c512 -r u6_eeprom_dump.bin

The tool detected the CH341 at 1a86:5512 in EPP/I2C mode and read all 65,536 bytes at 100kHz. I performed a second read to verify — both dumps are byte-identical (SHA-256: 54091da5bb3b40a1e909bf781e9a2abce1c6335d0c92f01741efad3fb9707bf3).

What we found

The EEPROM is only 26% utilized:

Region	Address Range	Size	Contents
Data	0x0000 – 0x4298	17,049 bytes	D2-81431 DSP firmware
Empty	0x4299 – 0xFFFF	48,487 bytes	Erased (0xFF)

17,049 bytes divides evenly into 5,683 24-bit words, which is exactly the word size of the D2Audio DSP architecture (Motorola 56300 family). This is not a coincidence — the entire data region is a stream of 24-bit DSP words packed big-endian into the EEPROM’s byte-addressable space.

The data is NOT encrypted

Initial byte-level entropy analysis looked discouraging — all 256 byte values present, roughly uniform distribution. But analyzing at the correct granularity, 24-bit words, told a very different story.

The critical finding: 70.3% of all 24-bit words have their least significant bit set to 0. Truly encrypted or scrambled data would show 50% ± 1%. A 20-point bias is a dead giveaway that we are looking at real coefficient data, not ciphertext.

Why the byte-level analysis was misleading

Byte-level entropy can look uniform even when the underlying 24-bit words have strong structure. A 24-bit coefficient like 0x2C4800 has three bytes (0x2C, 0x48, 0x00) that individually contribute to a flat byte histogram, but the word as a whole has a clear LSB of 0. The D2Audio DSP uses 24-bit fixed-point arithmetic (Q23 format), where small coefficient values naturally cluster around zero with even LSBs.

A reference to “encryption” in the Renesas EEPROM app note (R32AN0006) turned out to refer to encryption within the Audio Canvas III design files on the PC, not in the EEPROM image itself. The boot ROM loads EEPROM data raw.

Boot header

The first two 24-bit words form a complement pair:

• Word 0: 0x000008 (+8 in 24-bit signed)
• Word 1: 0xFFFFF8 (-8 in 24-bit signed)
• Sum = 0 in 24-bit arithmetic — a classic integrity check

This is consistent with a boot header that the D2-81431’s boot ROM validates before loading the rest of the image.

Regional structure

The LSB bias is not uniform across the image — it varies by region, revealing the internal structure of the firmware:

Word Range	Bit-0 = 0	Interpretation
0–499	53.2%	Near random — program code or boot header
500–5500	67–80%	Strong bias — coefficient and parameter data
5500+	55.7%	Returns toward random — possible program tail

The Hamming distance between adjacent words follows a near-perfect binomial distribution centered at 12 bits, consistent with independent coefficient values rather than structured program code.

Identified DSP filters

Analyzing 24-bit word quintuplets as potential biquad filter coefficients revealed recognizable audio processing stages. A second-order IIR biquad filter has the transfer function H(z) = (b0 + b1·z⁻¹ + b2·z⁻²) / (1 + a1·z⁻¹ + a2·z⁻²), requiring five coefficients per stage.

Subwoofer crossover (word 3299): b0 = −0.3476, b1 = −0.6833, b2 = −0.3120. The frequency response shows +47.5 dB at 20 Hz rolling off to −4.2 dB at 10 kHz — a textbook low-pass filter for subwoofer duty.

Subsonic high-pass stages: Multiple HPF groups found in words 0–500, consistent with subsonic rumble protection (removing content below approximately 20 Hz to protect the driver from inaudible excursion).

PWM correction filters: Approximately 20 filter groups with peaking behavior at 8–16 kHz, consistent with the D2-81431’s patented adaptive PWM frequency response correction — compensating for the output LC filter and speaker impedance characteristics.

Parametric EQ: Several groups matching peaking/parametric EQ patterns, likely the speaker EQ presets (FLAT and model-specific profiles that the front panel menu exposes).

Auto-correlation analysis reveals weak periodicity spikes at intervals of 6 and 12 words, consistent with the DSP’s biquad cascade structure: five coefficients per biquad plus one control/routing word equals six words per filter stage.

What the dump is good for

The EEPROM dump is a byte-perfect backup of the DSP firmware. If the EEPROM ever fails or gets corrupted — a real risk with a chip from 2007 that has been through thousands of thermal cycles — this dump can restore the amplifier’s audio processing to its exact factory state.

Beyond backup, the unencrypted nature of the data means the filter topology is partially readable. We can identify the crossover frequency, count the number of EQ stages, and verify the subsonic protection filters are present. A complete decode of the image structure would require either the Audio Canvas III tool (NDA-restricted) or a disassembly of the LPC2103F firmware, which contains the I2C protocol for writing to the D2-81431. The LPC2103F flash dump remains the next target — via JTAG through the 2x5 pin debug header on the controller board.