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4–4 Chapter 4: Functional Description

Receiver

Asynchronous Serial Interface (ASI) MegaCore Function User Guide January 2014 Altera Corporation

Synchronization State Machine

Two consecutive comma characters without any disparity or code error enables word

synchronization. Four consecutive disparity or code errors enables loss of

synchronization and so disable the word synchronization flag. The word

synchronization flag gates the rate matching FIFO write request. Figure 4–3 shows the

synchronization state machine.

Packet Synchronization

The packet synchronization block looks for the presence of valid TS packets. Valid

packets have either 188 bytes or 204 bytes between synchronization bytes. The

synchronization byte takes the value

0x47

The block first looks for the synchronization byte that indicates the start of the packet,

which is indicated by

rx_ts_status[1]

. The block then counts valid bytes in the

incoming stream. If a synchronization byte is seen 188 or 204 bytes after the first sync

byte is seen, lock is indicated on

rx_ts_[5:4]

and end of packet is indicated on

rx_ts_status[2]

. If no synchronization byte is seen at either 188 or 204 bytes, the

packet is deemed to have an error and

rx_ts_status[3]

is asserted. The block then

again starts the search for synchronization bytes.

Figure 4–3. Synchronization State Machine

SYNC_REQ 1

SYNC_REQ 2

IN_SYNC 1

! CODE_ERROR

CODE_ERROR

! CODE_ERRORCODE_ERROR

CODE_ERROR

! CODE_ERROR and

KCODE_FOUND

! CODE_ERROR and

KCODE_FOUND

! CODE_ERROR

IN_SYNC 2

IN_SYNC 3

IN_SYNC 4

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