Linux Kernel Driver

The dvb_usb_gp8psk module is a Linux kernel DVB-USB driver supporting multiple Genpix satellite receiver models. It communicates with the FX2 microcontroller via USB vendor control requests to manage tuning, demodulation, LNB control, DiSEqC switching, and transport stream capture.

Source files: drivers/media/usb/dvb-usb/gp8psk.c, gp8psk.h, gp8psk-fe.c

USB Device Table

USB ID	Device Name	cold_ids	warm_ids	FW01 Needed?
v09C0p0200	Rev.1 Cold	Yes	—	Yes
v09C0p0201	Rev.1 Warm	—	Yes	No (FW02 needed)
v09C0p0202	Rev.2	—	Yes	No
v09C0p0203	SkyWalker-1	—	Yes	No
v09C0p0204	SkyWalker-1 (alt)	—	Yes	No
v09C0p0206	SkyWalker CW3K	—	Yes	No

Note

PID 0x0205 (SkyWalker-2) is absent from the kernel 6.16.5 build. PID 0x0203 was not present in earlier kernel versions (e.g., v6.6.1) — it was added later as the SkyWalker-1 gained community attention.

Driver Architecture

The driver consists of three source files:

File	Purpose
gp8psk.c	USB device management, firmware loading, power control, vendor command wrappers
gp8psk.h	Vendor command constants, firmware version thresholds, USB PID definitions
gp8psk-fe.c	DVB frontend implementation: tuning, signal monitoring, LNB/DiSEqC callbacks

The driver registers with the DVB-USB framework (dvb_usb_device_properties) which handles:

• USB device enumeration and firmware download (for cold devices)
• DVB adapter and frontend creation
• URB management for bulk transport stream capture
• Power management callbacks

USB Transfer Parameters

Driver USB configuration

gp8psk_properties {
    .usb_ctrl                  = CYPRESS_FX2;
    .firmware                  = "dvb-usb-gp8psk-01.fw";
    .num_adapters              = 1;
    .generic_bulk_ctrl_endpoint = 0x01;
    // Streaming:
    .endpoint                  = 0x82;  // IN bulk
    .stream                    = USB_BULK;
    .count                     = 7;     // URBs
    .buffersize                = 8192;  // bytes per URB
}

The driver allocates 7 URBs of 8192 bytes each (56 KB total) for transport stream reception on endpoint 0x82 (IN bulk). Vendor commands use endpoint 0x01 with a 2000 ms timeout.

Retry Logic

IN operations retry up to 3 times if partial data is received. The command buffer is 80 bytes maximum:

Vendor command wrapper

static int gp8psk_usb_in_op(struct dvb_usb_device *d,
    u8 req, u16 value, u16 index, u8 *b, int blen)
{
    int ret;
    int try;
    for (try = 0; try < 3; try++) {
        ret = usb_control_msg(d->udev,
            usb_rcvctrlpipe(d->udev, 0),
            req, USB_TYPE_VENDOR | USB_DIR_IN,
            value, index, b, blen, 2000);
        if (ret == blen) break;
    }
    return ret;
}

Complete Vendor Command Map

Cmd	Name	Dir	wValue	wLength	Purpose
0x80	GET_8PSK_CONFIG	IN	0x0000	1	Read config status byte
0x81	SET_8PSK_CONFIG	OUT	varies	0	STALL (not implemented)
0x83	I2C_WRITE	OUT	dev_addr	N	Write to BCM4500 via I2C
0x84	I2C_READ	IN	dev_addr	N	Read from BCM4500 via I2C
0x85	ARM_TRANSFER	OUT	0/1	0	Start/stop TS streaming
0x86	TUNE_8PSK	OUT	0x0000	10	Send tuning parameters
0x87	GET_SIGNAL_STRENGTH	IN	0x0000	6	Read SNR values
0x88	LOAD_BCM4500	OUT	1	0	Initiate demod FW download
0x89	BOOT_8PSK	IN	0/1	1	Power on/off demodulator
0x8A	START_INTERSIL	IN	0/1	1	Enable/disable LNB supply
0x8B	SET_LNB_VOLTAGE	OUT	0/1	0	Set 13V (0) or 18V (1)
0x8C	SET_22KHZ_TONE	OUT	0/1	0	Enable/disable 22 kHz tone
0x8D	SEND_DISEQC	OUT	msg[0]	3-6	Send DiSEqC message
0x8E	SET_DVB_MODE	OUT	1	0	Enable DVB-S mode
0x8F	SET_DN_SWITCH	OUT	cmd	0	Legacy Dish switch command
0x90	GET_SIGNAL_LOCK	IN	0x0000	1	Read lock status
0x92	GET_FW_VERS	IN	0x0000	6	Read firmware version
0x94	USE_EXTRA_VOLT	OUT	0/1	0	Enable +1V LNB boost
0x95	GET_FPGA_VERS	IN	0x0000	1	Read hardware platform ID
0x99	GET_DEMOD_STATUS	IN	0x0000	1	Read BCM4500 reg 0xF9 (v2.13+)
0x9A	INIT_DEMOD	OUT	0x0000	0	Re-init demodulator (v2.13+)
0x9C	DELAY_COMMAND	OUT	param	0	Tuning delay with polling (v2.13+)
0x9D	CW3K_INIT	OUT	0/1	0	CW3K model initialization

Configuration Status Byte

GET_8PSK_CONFIG (0x80) returns a bit-mapped status register:

Bit 0 (0x01): bm8pskStarted    - Device booted and running
Bit 1 (0x02): bm8pskFW_Loaded  - BCM4500 firmware loaded
Bit 2 (0x04): bmIntersilOn     - LNB power supply enabled
Bit 3 (0x08): bmDVBmode        - DVB mode enabled
Bit 4 (0x10): bm22kHz          - 22 kHz tone active
Bit 5 (0x20): bmSEL18V         - 18V LNB voltage selected
Bit 6 (0x40): bmDCtuned        - DC offset tuning complete
Bit 7 (0x80): bmArmed          - MPEG-2 stream transfer armed

Boot Sequence

1. Read config (GET_8PSK_CONFIG 0x80): Check bit 0 (bm8pskStarted)

2. Boot device if not started: Send BOOT_8PSK 0x89 with wValue=1, then read firmware version via GET_FW_VERS 0x92

3. Load BCM4500 firmware if bit 1 not set: Only for Rev.1 Warm (PID 0x0201). Send LOAD_BCM4500 0x88 followed by firmware chunks. Skipped for SkyWalker-1 (bit already set from EEPROM boot).

4. Enable LNB if bit 2 not set: Send START_INTERSIL 0x8A with wValue=1

5. Set DVB mode: Send SET_DVB_MODE 0x8E with wValue=1 (STALL on some revisions)

6. Cancel pending stream: Send ARM_TRANSFER 0x85 with wValue=0

7. Ready for tuning

Tuning Flow

10-byte tuning payload

Bytes 0-3:  Symbol Rate    (u32 LE, in sps)
Bytes 4-7:  Frequency      (u32 LE, in kHz)
Byte 8:     Modulation     (0-9, see modulation types)
Byte 9:     FEC Rate       (index into firmware FEC table)

Modulation Types

Value	Constant	Mode
0	ADV_MOD_DVB_QPSK	DVB-S QPSK
1	ADV_MOD_TURBO_QPSK	Turbo QPSK
2	ADV_MOD_TURBO_8PSK	Turbo 8PSK
3	ADV_MOD_TURBO_16QAM	Turbo 16QAM
4	ADV_MOD_DCII_C_QPSK	Digicipher II Combo
5	ADV_MOD_DCII_I_QPSK	Digicipher II I-stream
6	ADV_MOD_DCII_Q_QPSK	Digicipher II Q-stream
7	ADV_MOD_DCII_C_OQPSK	Digicipher II Offset QPSK
8	ADV_MOD_DSS_QPSK	DSS/DIRECTV QPSK
9	ADV_MOD_DVB_BPSK	DVB-S BPSK

Signal Quality

GET_SIGNAL_STRENGTH (0x87) returns 6 bytes:

Bytes 0-1:  SNR value (u16 LE, in dBu*256 units)
Bytes 2-5:  Reserved / diagnostics

SNR scaling in the kernel: snr_value * 17 maps to the 0—65535 range. 100% signal quality corresponds to SNR >= 0x0F00.

Firmware Version Handling

The driver defines two version constants in gp8psk-fe.h:

Firmware version thresholds

#define GP8PSK_FW_REV1  0x020604    // v2.06.4
#define GP8PSK_FW_REV2  0x020704    // v2.07.4

< FW_REV1

Oldest firmware. No extended commands available.

>= FW_REV1

v2.06.4 baseline. All standard commands operational. Uses GET_SIGNAL_STRENGTH for BER monitoring.

>= FW_REV2

v2.07.4+. Enables additional code paths:

• GET_DEMOD_STATUS (0x99) for demod health check
• INIT_DEMOD (0x9A) for demod re-initialization
• DELAY_COMMAND (0x9C) for tuning acquisition delays
• Different signal quality calculation

Command Correlation with Firmware

Not all vendor commands work on all firmware versions. The STALL behavior varies:

Command	v2.06 FW	v2.13 FW	Rev.2 FW	Custom v3.01
0x80 GET_8PSK_CONFIG	OK	OK	OK	OK
0x86 TUNE_8PSK	OK	OK	OK	OK
0x87 GET_SIGNAL_STRENGTH	OK	Changed	OK	OK
0x88 LOAD_BCM4500	STALL	STALL	STALL	STALL
0x99 GET_DEMOD_STATUS	STALL	OK	Proto	N/A
0x9A INIT_DEMOD	STALL	OK	Proto	N/A
0x9C DELAY_COMMAND	STALL	OK	N/A	N/A

Note

Command 0x88 (LOAD_BCM4500) routes to the STALL handler in all extracted firmware versions. The kernel only sends it for Rev.1 Warm devices (PID 0x0201) after confirming bm8pskFW_Loaded is not set. On SkyWalker-1 hardware, the BCM4500 firmware is in ROM, so this bit is always set at boot.

Kernel Module Parameters

The gp8psk module inherits standard DVB-USB parameters:

Parameter	Default	Description
debug	0	Enable debug logging (bitmask)
force_pid_filter	0	Force PID filtering on/off
generic_bulk_ctrl_endpoint	0x01	Control endpoint

Enable verbose logging with:

modprobe dvb_usb_gp8psk debug=0xff

Or at runtime:

echo 0xff > /sys/module/dvb_usb_gp8psk/parameters/debug

DVB Frontend Properties

The gp8psk frontend (gp8psk-fe.c) registers with the following capabilities:

Frontend info structure

.name                  = "Genpix 8psk-to-USB2 DVB-S"
.frequency_min_hz      = 800  * MHz
.frequency_max_hz      = 2250 * MHz
.frequency_stepsize_hz = 100  * kHz
.symbol_rate_min       = 256000     // 256 Ksps
.symbol_rate_max       = 30000000   // 30 Msps
.caps = FE_CAN_INVERSION_AUTO |
        FE_CAN_FEC_1_2 | FE_CAN_FEC_2_3 |
        FE_CAN_FEC_3_4 | FE_CAN_FEC_5_6 |
        FE_CAN_FEC_7_8 | FE_CAN_FEC_AUTO |
        FE_CAN_QPSK

Note

The frontend capabilities only advertise FE_CAN_QPSK — the turbo 8PSK, turbo 16QAM, and DCII modes are not exposed through the standard DVB API. Accessing these modes requires direct vendor command access or the Windows BDA driver.

Related Pages

• Vendor Commands — Complete command reference
• Kernel FW01 — Firmware format and loading analysis
• DVB-S2 Investigation — Why DVB-S2 cannot be added
• Custom Firmware v3.01 — Open-source replacement with extended commands