DVB-S2 Incompatibility

Danger

DVB-S2 is not supported on the SkyWalker-1. This is a fundamental hardware limitation of the Broadcom BCM4500 demodulator silicon, not a firmware limitation. No firmware update can add DVB-S2 capability. The BCM4500 was designed and fabricated before the DVB-S2 standard was ratified (March 2005) and contains no LDPC or BCH decoder hardware.

The Core Problem

DVB-S2 (ETSI EN 302 307) requires two forward error correction technologies that do not exist in the BCM4500:

FEC Component	BCM4500 Has	DVB-S2 Requires
Inner code	Viterbi (convolutional) + Turbo	LDPC (Low-Density Parity-Check)
Outer code	Reed-Solomon (t=10)	BCH (Bose-Chaudhuri-Hocquenghem)
Block size	Streaming (Viterbi) or short turbo blocks	64,800 or 16,200 bits
Decoder type	Trellis-based / iterative turbo	Iterative belief propagation

LDPC decoding requires dedicated silicon: large block RAM for message passing (the LDPC block is 64,800 bits), iterative belief propagation logic, and a fundamentally different decoder architecture. This cannot be emulated in firmware on the BCM4500’s simple 8-bit on-chip microcontroller, which handles only configuration, acquisition, and monitoring — not data-path processing.

BCM4500 FEC Architecture

The BCM4500 contains exactly two FEC decoder paths (from the BCM4500 datasheet):

Legacy FEC

Viterbi + Reed-Solomon (Legacy)

Used for DVB-S QPSK, DSS QPSK, DVB-S BPSK, and Digicipher II modes.

Parameter	Value
Inner decoder	Viterbi (convolutional)
Code rates	1/2, 2/3, 3/4, 5/6, 7/8
Outer decoder	Reed-Solomon
Signal path	Soft decisions fed to Viterbi, then RS outer code
Modulations	BPSK, QPSK

Firmware evidence (XRAM 0xE0F9): FEC lookup table with max index 7. Modulation dispatch sets XRAM 0xE0F6 = 0x00 (turbo flag OFF), XRAM 0xE0F5 = 0x10 (standard demod mode).

Windows driver: m_CurResource.ulInnerFecType = BDA_FEC_VITERBI — explicitly rejects any FEC type other than Viterbi.

Turbo FEC

Turbo Code Decoder (Proprietary)

Used for Turbo QPSK, Turbo 8PSK, and Turbo 16QAM — proprietary “advanced modulation” modes developed by Broadcom for EchoStar/Dish Network.

Parameter	Value
Inner decoder	Iterative turbo code
QPSK rates	1/4, 1/2, 3/4
8PSK rates	2/3, 3/4, 5/6, 8/9
16QAM rates	3/4
Outer decoder	Reed-Solomon (t=10)
Modulations	QPSK, 8PSK, 16QAM

Firmware evidence (XRAM 0xE0B7, 0xE0B1, 0xE0BC): Turbo FEC lookup tables. All turbo modes set XRAM 0xE0F6 = 0x01 (turbo flag ON).

These turbo codes are NOT the same as DVB-S2’s LDPC codes. The turbo decoder uses parallel concatenated convolutional codes, while LDPC uses sparse parity-check matrix belief propagation. Different algorithms, different silicon.

Digicipher II

DCII Decoder

Used for DCII combo, split I/Q, and offset QPSK modes.

Parameter	Value
FEC table	XRAM 0xE0BD, max index 9
Fixed FEC code	0xFC written to XRAM 0xE0EB
Modulations	QPSK variants (combo, split, offset)

The BCM4500 datasheet states explicitly: “Optimized soft decisions are then fed into either a DVB/DIRECTV/DCII-compliant FEC decoder, or an advanced modulation turbo decoder.” These are the only two FEC paths. There is no third path for LDPC/BCH.

Zero DVB-S2 Evidence in Firmware or Driver

Exhaustive search across all firmware versions and Windows driver source:

What Was Searched	Result
All firmware binaries (v2.06, Rev.2, v2.13) via Ghidra	No LDPC/BCH/DVB-S2 references
Windows driver SkyWalker1Control.h	Modulation constants 0—9 only, none for DVB-S2
Windows driver SkyWalker1TunerFilter.cpp	Rejects non-Viterbi FEC types
Windows driver SkyWalker1Control.cpp	Hardcodes ADV_MOD_DVB_QPSK (value 0)
Firmware dispatch table (CODE:0873)	10 entries max, values >= 10 rejected
All FEC lookup tables in XRAM	Only Viterbi rates and turbo rates, no LDPC rates
I2C register addresses	BCM4500-specific protocol only (page 0x00, regs 0xA6/A7/A8)

Specific proof points:

• SkyWalker1TunerFilter.cpp, line 1070: if(ulNewInnerFecType == BDA_FEC_VITERBI) — only Viterbi accepted; any other FEC type returns STATUS_INVALID_PARAMETER
• SkyWalker1Control.cpp, line 292: ucCommand[8] = ADV_MOD_DVB_QPSK; — always sends modulation type 0
• Firmware jump table at CODE:0866: bounds check rejects modulation values >= 10

Is the USB Data Path a Bottleneck?

No. The GPIF/USB 2.0 streaming architecture has roughly 5x headroom for DVB-S2 data rates. The bottleneck is the demodulator silicon, not the transport path.

Metric	Value
DVB-S2 max net rate (8PSK 9/10, 30 Msps)	~58 Mbps (~7.25 MB/s)
Typical HD transponder (8PSK 3/4, 27.5 Msps)	~44 Mbps
USB 2.0 practical bulk throughput	~280 Mbps (~35 MB/s)
GPIF engine theoretical throughput (48 MHz, 8-bit)	384 Mbps (48 MB/s)
Current DVB-S typical TS rate	1—5 MB/s

DVB-S2 uses the same MPEG-TS output format (188-byte packets) as DVB-S, so the GPIF waveform and AUTOIN configuration would work unchanged.

However, this is a moot point: even if the BCM4500 were physically replaced with a DVB-S2-capable chip, the entire FX2 firmware would need rewriting (I2C register protocol, tuning sequence, modulation dispatch, FEC configuration), since every DVB-S2 demodulator uses a completely different register interface.

Broadcom’s DVB-S2 Silicon Timeline

Broadcom addressed DVB-S2 by designing entirely new chips — they did not add LDPC to the BCM4500:

Chip	Year	DVB-S2	Key Addition
BCM4500	~2003	No	Turbo FEC + Viterbi/RS
BCM4501	2006	Yes	First dual-tuner DVB-S2; LDPC/BCH decoder
BCM4505	2007	Yes	Single-channel, 65nm, LDPC/BCH + legacy
BCM4506	2007	Yes	Dual-channel, 65nm, LDPC/BCH + legacy

The BCM4501 datasheet explicitly states it includes “four 8-bit ADCs, all-digital variable rate QPSK/8PSK receivers, advanced modulation LDPC/BCH, and DVB-S-compliant forward error correction decoder.” Adding LDPC/BCH required new silicon.

Note

Broadcom restricted sales of the BCM4501/4505/4506 to set-top box manufacturers (EchoStar, DIRECTV). They did not sell to PC peripheral makers. This is why Genpix could not simply drop in a BCM4501 as a replacement.

What Genpix Did: The SkyWalker-3

Genpix released the SkyWalker-3 as a DVB-S2-capable successor using a completely different demodulator (likely STMicroelectronics STV0903):

Feature	SkyWalker-1 (BCM4500)	SkyWalker-3 (likely STV0903)
DVB-S QPSK	Yes	Yes
DVB-S2 QPSK	No	Yes
DVB-S2 8PSK	No	Yes
Turbo QPSK	Yes	No
Turbo 8PSK	Yes	No
Turbo 16QAM	Yes	No
DCII	Yes	Yes
DSS	Yes	Yes
Symbol rate (DVB-S)	256 Ksps — 30 Msps	1 — 45 Msps
Symbol rate (DVB-S2)	N/A	5 — 33 Msps
FEC inner (DVB-S)	Viterbi	Viterbi
FEC inner (DVB-S2)	N/A	LDPC
FEC outer (DVB-S2)	N/A	BCH

The trade-off is clear: the SkyWalker-3 gained DVB-S2 but lost turbo-FEC support entirely. The turbo codes were proprietary to Broadcom/EchoStar, and the STV0903 does not implement them. This means the SkyWalker-3 cannot receive Dish Network’s legacy turbo-coded 8PSK transmissions.

Summary

Question	Answer
Is DVB-S2 a hardware or firmware limitation?	Hardware — BCM4500 has no LDPC/BCH decoder
Could a firmware update add DVB-S2?	No — LDPC requires dedicated silicon
Which Broadcom chip first added LDPC?	BCM4501 (2006)
Any DVB-S2 hints in firmware/driver?	None — zero references anywhere
Is the USB data path a bottleneck?	No — ~5x headroom for DVB-S2 rates
What did Genpix do for DVB-S2?	Released SkyWalker-3 with STV0903 demodulator
What was lost in the SkyWalker-3?	Turbo-FEC support (Broadcom/EchoStar proprietary)