GreenPAK Universal Dev Board 1

This page describes the USB protocol used by the GreenPAK Universal Dev Board 1, as shipped in the GreenPAK 4 Development Kit and probably others as well. Protocol RE is done by @whitequark with board revision v1.3.1 and firmware v2.4.

The board speaks two protocols, both of which are based on USBHID. They use interrupt URBs, always with a 64 byte payload. All numbers below are in hexadecimal.

Bootloader protocol

After plugging in, the board lights up a white LED and enumerates as 0f0f:8006. In this state it is not operational, and it is necessary to send it a command to make it so. The Silego tool will proceed to chat a bit with it in a protocol that is not readily identifiable, but most of it does not appear to be necessary.

Overall payload format:

Offset	Length	Meaning
00	3c	Unknown
3c	01	Command
3d	03	Unknown

The command 09, with the rest of the packet being zeroed, switches the board into operational mode. All other commands are not understood.

Main protocol

After switching mode, the board lights up an orange LED and enumerates as 0f0f:0006.

Overall payload format:

Offset	Length	Meaning
00	01	Sequence number A (SEQA)
01	01	Packet type
02	01	Packet length
03	01	Sequence number B (SEQB)

The function of sequence numbers A and B is not fully understood. Under most circumstances sequence number A is 01 and sequence number B is 00.

The packet length is offset by one. I.e. it is the index of the last meaningful byte in the URB payload.

Every byte not specified in the individual packet format was always observed as 00.

"Read back command for ..." means that the returned payload for this READ command is exactly the same as what was provided for the WRITE command it refers to.

Packets

WRITE 02

This command starts transferring the bitstream out of the device.

Offset	Length	Meaning
04	03	Unknown; observed as c007d0
07	02	The total number of SCL cycles to use (see WRITE 03)

WRITE 03

This command transfers the bitstream to the device.

With SEQA=01, SEQB=04:

Offset	Length	Meaning
04	03	Unknown; observed as 080000
07	02	The number of SCL cycles to use
09	37	reg<0:439>

With SEQA=02, SEQB=03:

Offset	Length	Meaning
04	3c	reg<440:919>

With SEQA=03, SEQB=02:

Offset	Length	Meaning
04	3c	reg<920:1399>

With SEQA=04, SEQB=01:

Offset	Length	Meaning
04	3c	reg<1400:1879>

With SEQA=05, SEQB=00:

Offset	Length	Meaning
04	15	reg<1880:2047>

WRITE 04

This packet configures the I/O buffers, LEDs, and the expansion connector.

Format:

Offset	Length	Meaning
04	02	TP2 output configuration
06	02	TP3 output configuration
08	02	TP4 output configuration
0a	02	TP5 output configuration
0c	02	TP6 output configuration
0e	02	TP7 output configuration
10	02	TP8 output configuration
12	02	TP9 output configuration
14	02	TP10 output configuration
16	02	TP12 output configuration
18	02	TP13 output configuration
1a	02	TP14 output configuration
1c	02	TP15 output configuration
1e	02	TP16 output configuration
20	02	TP17 output configuration
22	02	TP18 output configuration
24	02	TP19 output configuration
26	02	TP20 output configuration
2f	03	Expansion connector configuration
32	01	TP3..TP6 LED configuration
33	01	TP7..TP10 LED configuration
34	01	TP12..TP15 LED configuration
35	02	TP16..TP20 LED configuration
37	03	Unknown; observed as 010000

TPx output configuration:

Value	Meaning
0200	N/C
0c01	VDD
0c00	GND
0e01	Pull-up
0e00	Pull-down
0c03	Logic generator, push-pull
0403	Logic generator, open-drain + pull-up
0603	Logic generator, open-drain + pull-down
0a03	Logic generator, open-drain, drives HI
0803	Logic generator, open-drain, drives LO
0e03	Logic generator, pull-up/down

TP3..TP6, TP7..TP10 and TP12..TP15 LED configuration (a bit mask):

Value	Meaning
01	TP(n+0) LED enabled
02	TP(n+1) LED enabled
04	TP(n+2) LED enabled
08	TP(n+3) LED enabled
10	TP(n+0) LED inverted
20	TP(n+1) LED inverted
40	TP(n+2) LED inverted
80	TP(n+3) LED inverted

TP16..TP20 LED configuration (a bit mask):

Value	Meaning
0100	TP(n+0) LED enabled
0200	TP(n+1) LED enabled
0400	TP(n+2) LED enabled
0800	TP(n+3) LED enabled
1000	TP(n+4) LED enabled
0001	TP(n+0) LED inverted
0002	TP(n+1) LED inverted
0004	TP(n+2) LED inverted
0008	TP(n+3) LED inverted
0010	TP(n+4) LED inverted

Expansion connector configuration (a bit mask):

Value	Meaning
000100	VDD
000004	TP2
000001	TP3
000010	TP4
000040	TP5
010000	TP6
040000	TP7
100000	TP8
400000	TP9
800000	TP10
200000	TP12
000008	TP13
000002	TP14
008000	TP15
000020	TP16
020000	TP17
002000	TP18
000800	TP19
080000	TP20

WRITE 05

This packet (likely) resets the board controller.

READ 05

Response to WRITE 05; reset acknowledgement.

WRITE 07

This command continues transferring the bitstream out of the device.

Offset	Length	Meaning
04	03	Unknown; observed as c007d0
07	02	The total number of SCL cycles to use (see WRITE 03)

READ 07

Response to WRITE 03; bitstream acknowledgement, more data required.

WRITE 08

This command confgiures a signal generator.

Offset	Length	Meaning
04	01	Generator type; 01=logic generator, 02=signal generator
05	01	Test point index; 01=VDD, 02=TP2, ..., 0a=TP10, 0c=TP12, ..., 14=TP20
06	01	Pre-start state; 00=low, 01=start point, 02=hi-Z
07	01	Repeat count; 00=forever, 01=once, 02=twice, ...
08	01	End state; 00=pre-start state, 01=keep last state
09	02	Initial voltage
11	02	Point 1: ramp delay
13	02	Point 1: ramp voltage, integral step part
15	02	Point 1: ramp voltage, step sign and fractional step part
17	02	Point 2: ramp delay
19	02	Point 2: ramp voltage, integral step part
1b	02	Point 2: ramp voltage, step sign and fractional step part
...	...	...

Voltages are specified with 1LSB corresponding to 1.362mV. Tolerance is ±30mV on VCC and ±7mV on all other outputs.

Delays are specified with 1LSB corresponding to 0.1ms, with 0000 corresponding to the delay of 0.1ms.

Ramping is specified as follows. Every 0.1ms, the voltage is increased by a 16.15 fixed point number comprised by the entire integral and low 15 bits of the fractional ramp voltage parts. The sign of this number is specified by bit 15 of the fractional ramp voltage part.

WRITE 09

This command starts or stops one or more signal generators at once.

Offset	Length	Meaning
04	01	VDD generator command
05	01	TP2 generator command
06	01	TP3 generator command
07	01	TP4 generator command
08	01	TP5 generator command
09	01	TP6 generator command
0a	01	TP7 generator command
0b	01	TP8 generator command
0c	01	TP9 generator command
0d	01	TP10 generator command
0e	01	TP12 generator command
0f	01	TP13 generator command
10	01	TP14 generator command
11	01	TP15 generator command
12	01	TP16 generator command
13	01	TP17 generator command
14	01	TP18 generator command
15	01	TP19 generator command
16	01	TP20 generator command

Generator command:

Value	Meaning
00	Pause
01	Start
02	Stop
03	NOP

READ 13

Response to WRITE 02 and WRITE 07.

The exact placement of the bitstream is not yet documented.

READ 1a

Response to WRITE 03; bitstream acknowledgement, no more data required.

WRITE 21

This command turns the STATUS LED on and off.

Offset	Length	Meaning
04	01	STATUS LED enabled

READ 21

Response to WRITE 21; STATUS LED change acknowledgement.

WRITE 25

This command chooses the part that the board will interface with.

Offset	Length	Meaning
04	04	Part ID

Part IDs:

Value	Meaning
11000000	Unknown
14000000	Unknown
62000000	SLG46620V
72000000	Unknown
62000000	Unknown

READ 25

Response to WRITE 25; part change acknowledgement.

WRITE 42

This command measures the oscillator frequency.

Offset	Length	Meaning
04	01	Unknown; observed as 00

READ 42

Response to WRITE 42; measured oscillator frequency.

Offset	Length	Meaning
04	02	Unknown; observed as 0000
06	02	Oscillator frequency

WRITE 49

This command trims the oscillator.

Offset	Length	Meaning
04	01	Unknown; observed as 00
05	01	Trim value
06	06	Unknown; observed as 05040a110201

READ 49

Response to WRITE 49; oscillator trimming acknowledgement.

Offset	Length	Meaning
04	02	Unknown; observed as 0000
06	06	Unknown; observed as 05040a110201

Command sequences

Trimming

In a loop, searching by changing the trim value between ff to 00:

1. WRITE 49
2. READ 49
3. WRITE 42
4. READ 42

Downloading

1. WRITE 03 SEQA=01 SEQB=04
2. READ 07
3. WRITE 03 SEQA=02 SEQB=03
4. READ 07
5. WRITE 03 SEQA=03 SEQB=02
6. READ 07
7. WRITE 03 SEQA=04 SEQB=01
8. READ 07
9. WRITE 03 SEQA=05 SEQB=00
10. READ 1a

Uploading

1. WRITE 02
2. READ 13 SEQB=04
3. WRITE 07
4. READ 13 SEQB=04
5. WRITE 07
6. READ 13 SEQB=04
7. WRITE 07
8. READ 13 SEQB=04
9. WRITE 07
10. READ 13 SEQB=04