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 ca bles/fibers are used between the control room of the experiment and the embe dded SCA and to support the relatively slow buses.

GBT SCA TX RX GBTx ASIC E-link HDLC MHz DDR = 80 Mbps (ISO/IEC 13239:2002) HDLC : High Level data Link control Elink is full duplex, Non deterministic link latency

HDLC Overview Broadly 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 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 commands 1.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 ( payload ) upper layer sets the pkt length (bytes) Upper layer sets the go bit Serialize the content from FIFO Set the busy bit during transmission If HDLC line is idle serial output set to high Wait for the first HDLC flag ( ) Move data to RX FIFO length count = Length count +1 If ( ) 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