README.md

pipistrello-TOSlink

TOSLink fibre data capture for Pipistrello (Xilinx SPARTAN 6)

What is this?

This project contains the Verilog and Visual Studio source files to allow a Saanlima Pipistrello board (containing a Xilinx SPARTAN 6 FPGA) to be used, in conjunction with a TOSLink receiver module, to capture data directly from a TOSLink fibre-optic input. Data is buffered in the onboard LPDDR memory on the Pipistrello and can be read back by a PC attached using a USB cable.

Here's a photo showing the setup running with some debug output on an oscilloscope:

How does it work?

The board is configured with its FTDI chip in USB Async FIFO mode, and with the TOSLink receiver module connected to pin 13 of the Wing A connector. The FPGA is configured to read commands from the FTDI chip. Supported commands are as follows:

0 - CMD_NOP

Offset	Size (bits)	Value
0	32	0 - CMD_NOP

Does nothing

1 - CMD_READ

Offset	Size (bits)	Value
0	32	1 - CMD_READ
4	32	address
8	32	count

Reads count 32-bit words from the onboard LPDDR memory, starting at address.

2 - CMD_WRITE

Offset	Size (bits)	Value
0	32	2 - CMD_WRITE
4	32	address
8	32	count
12	32 * count	Data to write

Writes count 32-bit words to the onboard LPDDR memory, starting at address.

3 - CMD_CAPTURE

Offset	Size (bits)	Value
0	32	3 - CMD_CAPTURE
4	32	count

Starts capturing data from the TOSLink input, writing it to memory starting at address 0 in the LPDDR memory. Capture will stop when count frames have been captured from the TOSLink input.

4 - CMD_STATUS

Offset	Size (bits)	Value
0	32	4 - CMD_STATUS

Requests status information from the FPGA. This returns a status packet, as follows:

Offset	Size (bits)	Value
0	32	flags
4	32	frames_remaining

The flags field is as follows:

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
																														done	sync

where sync indicates that the FPGA has acheived data synchronisation on the TOSLink input and done indicates that capture has completed.

The frames_remaining field is the number of frames left to capture from the TOSLink input.

5 - CMD_CHSTATUS

Offset	Size (bits)	Value
0	32	5 - CMD_CHSTATUS

Retrieve channel status data captured by the FPGA. This is a convenience, in that you could extract it in software from the captured data, but it's somewhat easier to do in the hardware than it is to do later in software.

(The channel status data is information sent along with the sample data in the TOSLink bit stream; there are 192 bits per block, one bit per frame, so this command response with 24 octets of data.)

Windows Software

The "toslink" folder contains the sources for a command line program that lets you easily send commands to the FPGA and displays the responses where appropriate.

You will need the FTDI SDK installed to build the code. Very likely you will need to edit the project's "VC++ Directories" settings to add the path to the FTDI SDK. You can download the files you need from

https://www.ftdichip.com/Drivers/D2XX.htm

Once it's built, you can run the program to get a list of the FTDI devices connected over USB. If you then re-run the program, passing either the description or serial number as an argument, the program will connect to that FTDI device and is ready to send commands. It's probably best only to connect to a Pipistrello board that has been programmed using the Verilog code from this project (otherwise who knows what will happen?!)

Once connected, you'll see a command prompt:

>

Available commands are:

exit

Terminate the program.

quit

Terminate the program.

purge

purge
purge rx
purge tx
purge all

Tell the FTDI library to purge any buffered data. Optionally you can specify rx, tx or (the default) all to control purging in individual directions.

This is mainly useful when debugging.

read

read <address> <count>

Read count words from address address and display them as a hex dump. You can specify address and count in hexadecimal if you wish by prefixing them with 0x.

save

save <address> <count> <filename>

Read count words from address address and save them to disk in filename as raw binary data.

capture

capture <count>

Start capturing frames from the TOSLink interface. count specifies the maximum number of frames to capture; after that many have been read, capture will cease.

status

status

Display current FPGA status, for instance

Synchronized, Running, 38 frames left

If synchronization with the incoming TOSLink signal is lost, LOS will be displayed instead of Synchronized. If capture is not currently in progress, Done will appear rather than Running.

chstatus

chstatus

Display the captured channel status data, in hexadecimal format.