PRON-Protokoll

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RZL1337 PRON-Wall Protocol Juli 2011

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1 Introduction

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This PRON-Wall Protocol (PWP) is defined to make available a datagram mode of communicating with a series of dot matrix light panels working together to form a display. This protocol assumes that the ethernet protocol [1] is used as the underlying protocol.

This protocol provides a procedure for application programs to send messages to light panels with a minimum of protocol mechanism. The protocol is transaction oriented.

1.1 Terminology

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panel

     A device connected to the network, with a unique MAC address.
     

subpanel

     A logical unit for displaying pictures. All Subpanels belong to a panel.

display

     The set of panels logically connected to the same Ethernet segment.

client

     The system that sends requests to the display (user equipment).

1.2 Hardware setup

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A display has one ethernet interface (RJ45), power supply and two cinch sockets to daisy chain the common interrupt line. Displays are addressed by their MAC address (or via broadcast).

2 Communication

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The following types of frames and packets are used for communication purposes. The communication is structured into two parts: the first part deals with the configuration of the panel devices and client software, the second part is used for the actual image frame transmission and processing. All communication is based on the Ethernet protocol.

2.1 Ethernet Frame

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             0      8     16    24                          63 
             +-----+-----+-----+-----+-----+-----+-----+-----+
             |  T  |  V  |  S  |              R              |
             +-----+-----+-----+-----+-----+-----+-----+-----+

| Payload ...

             +-----+-----+-----+-----...

   T ... Packet type
   V ... Version of the protocol (should be 23 for the first version)
   S ... Subpanel ID
   R ... Reserved

   Ethertype: 0x2342

2.2 Packet Types

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The first bit of the packet type defines whether is a request or reply.

   0xxxxxxx ... request message
   1xxxxxxx ... reply message

There are

   0x00 ... Scan Request
   0x80 ... Scan Reply
   0x01 ... Echo Request
   0x81 ... Echo Reply
   0x02 ... Set Master Request
   0x82 ... Set Master Reply
   0x03 ... Frame
   0x83 ... Frame Acknowledgement

2.2.1 Scan Request Payload

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0 n +---+---+---+---+ | R | +---+---+---+---+

   R ... Reserved

2.2.2 Scan Reply Payload

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0 1 15 16 23 24 31 32 39 +-+-----+-------+-------+-------+-------+ |T| BUFSZ | COLR | COLG | COLB | +-+-----+-------+-------+-------+-------+ | REF | NSUBP | SUBPR | X1 | +-------+-------+-------+-------+-------+ | Y1 | ... +-------+...

   T      ... Type of display (1 = RGB / 0 = Monochromatic)	
   BUFSZ  ... Buffer size in frames of the panel
   COLR   ... Color of panel (Red value)
   COLG   ... Color of panel (Green value)
   COLB   ... Color of panel (Blue value)
   REF    ... Refresh rate of the panel (Hz)
   NSUBP  ... Number of subpanels in this panel
   SUBPR  ... Subpanels per row
   X(1-N) ... Panel Width in pixels
   Y(1-N) ... Panel Height in pixels

There are as many X,Y pairs as indicated in NSUBP. If NSUBP%SUBPR != 0, the last row of subpanels consists of less subpanels than the other rows. "Color of panel" could be used for identification in the client UI.

2.2.3 Echo Request Payload

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   0    8   16  24  32
   +---+---+---+---+---+---+---+---+
   |       R       |       ID      |
   +---+---+---+---+---+---+---+---+

   R  ... Reserved
   ID ... ID of the Echo Request. Should be returned by the other endpoint.

2.2.4 Echo Reply Payload

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   +---+---+---+---+---+---+---+---+
   |       R       |       ID      |
   +---+---+---+---+---+---+---+---+

   R  ... Reserved
   ID ... ID of the Echo Request as sent by the client.

2.2.5 Set Master Request Payload

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   +---+---+---+---+---+---+---+---+---+---+
   |       R       | MAC ADDRESS OF MASTER |
   +---+---+---+---+---+---+---+---+---+---+

2.2.6 Set Master Reply Payload

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   +---+---+---+---+
   |     R     | I |
   +---+---+---+---+

   R ... Reserved
   I ... Feedback. 1 if the selected Panel is now the Master. 0 if not.

3 Master Autodiscovery

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Upon bootup, a device waits at least one interrupt interval plus an additional random backoff timer. If, during that time, no interrupt was recognized on the input line, the device sets up an interrupt by itself and thus serves as the master. Also, it informs the connected client about this decision so that unlikely, but possible collisions (several masters) can be detected and resolved by the client.

4 Image Frames

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Each frame contains a single image with brightness levels. This image can either be a greyscale image or one of the three base colors (R,G,B).

The protocol also supports 3D displays. The two most significant bits are designated for those frames. The most significant bit marks frames that are part of a 3D picture, the second one designates a frame for the left eye when it is not set and for the right eye when set.

4.1 Image Frame

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   0    8   16  24    32
   +---+---+---+---+---+
   | C | TIME  |  SEQ  |
   +---+---+---+---+---+
   |       PIXELS ... 
   ----------...

   C     ... type of frame (see 4.2)
   TIME  ... duration in milliseconds frame will be displayed
   SEQ   ... will be used for retransmissions
   PIXEL ... each pixel is represented by a single byte, containing the
             brightness level of this pixel

4.2 Image Frame Types

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PWP supports monochromatic/greyscale, 3D and RGB frames. 3D can be achieved using the shutter technique with an infrared LED serving as the synchronization clock generator.

   00xxxxxx ... normal frame
   1xxxxxxx ... 3D frame
   10xxxxxx ... 3D frame for left eye
   11xxxxxx ... 3D frame for right eye
   xxxxxx00 ... greyscale frame
   xxxxxx01 ... red frame
   xxxxxx10 ... blue frame
   xxxxxx11 ... green frame

4.3 Sequence number

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A sequence number designates the current full picture.