GBT SCA overview Slide 1-5

Work status Slide 6-10

Shuaib Ahmad Khan

The GBT Front-End System

The SCA top level diagram

Primary e-Link

Secondary e-Link

Dual Redundant e-link ports connections

Redundant schemes failure on the optical links(only one of the e-ports is active at any moment)

Both the e- ports communicate with the N/w controller via Atlantic interface N/W Controller connects further with all the interface channels via a common Wishbone bus.

The communication architecture used by the SCA is based on two protocol layers 1. The e link transport protocol ‑2. The SCA channel command protocol. The dual network architecture is necessary to support applications where long cables/fibers are used between the control room of the experiment and the embedded SCA and to support the relatively slow buses.

GBT SCA TX

RX

GBTx ASIC

E-link HDLC protocol@40 MHz DDR = 80 Mbps

(ISO/IEC 13239:2002)

HDLC : High Level data Link control

Elink is full duplex , Non deterministic link latency

HDLC OverviewBroadly HDLC features are as follows:• Reliable protocol

– selective repeat or go-back-N• Full-duplex communication

– receive and transmit at the same time• Bit-oriented protocol

– use bits to stuff flags occurring in data . i.e, it does NOT recognize or interpret byte value• Flow control

– adjust window size based on receiver capability• Uses physical layer clocking and synchronization to send and receive frames

• Defines three types of stations– Primary– Secondary– Combined

• Defines three types of data transfer mode– Normal Response mode– Asynchronous Response mode– Asynchronous Balanced mode

• Three types of frames– Unnumbered– information– Supervisory

HDLC data packet

• When no information Idle packet transmitted by the master interface and discarded at the receiver (idle packet is single bit long) SOF Address Field Control Field DATA FCS• Bit Stuffing Technique to implement a frame delimiter character “111111” (six 1’s)(Protocol ensures that this combination is not found anywhere else in the data bit stream)• Bits with in the frame are transmitted from LSB to MSB • SOF/EOF = binary 01111110• GBT-SCA Address packet destination address is 0x00 (default)• Control Field 1 byte Length and has the frame seq no. of the currently trans and lastly received frame. Packets no. from (0 – 7), max 8 unique no. packets in the link• Receiver : checks every received packet no. against the last one received SREJ command in case packets are missing Control Field is also used to convey three supervisory level commands1. Connect 2. RESET 3. TEST ( Slave generates Ack command in response, then only the next command) • Payload Multiple of 16 bits • FCS

HDLC Package from the upper

layer

HDLC package in a 8 bit wide FIFO (01111110 + payload + 01111110 + 11111111)

upper layer sets the pkt length (bytes)Upper layer sets the go bit

Serialize the content from

FIFO

Set the busybit during

transmission

If HDLC line is idle

serial output set to high

Wait for the first HDLC flag

(01111110)

Move data to RX FIFO

length count = Length count +1

If (01111110)Length count fixed

SCA Controller Tx state machine SCA Controller Rx state machine

If serial line is idle/high

packet received indication

Packet arrived flag set