GRSPW datasheet(7/48 Pages) ACTEL

7 / 48 page

GRSPW / GRSPW-FT

December 2008, Version 1.0.2

GAISLER

the signal and character levels of the SpaceWire standard is handled in the transmitter. External LVDS

drivers are needed for the data and strobe signals.

A transmission FSM reads N-Chars for transmission from the transmitter FIFO. It is given packet

lengths from the DMA interface and appends EOPs/EEPs and RMAP CRC values if requested. When

it is finished with a packet the DMA interface is notified and a new packet length value is given.

2.3.3

Receiver

The receiver detects connections from other nodes and receives characters as a bit stream on the data

and strobe signals. It is also located in a separate clock domain which runs on a clock generated from

the received data and strobe signals. More information on the clock-generation can be found in sec-

tion 2.8.1.

The receiver is activated as soon as the link interface leaves the error reset state. Then after a NULL is

received it can start receiving any characters. It detects parity, escape and credit errors which causes

the link interface to enter the error reset state. Disconnections are handled in the link interface part in

the system clock domain because no receiver clock is available when disconnected.

Received Characters are flagged to the host domain and the data is presented in parallel form. The

interface to the host domain is shown in figure 7. L-Chars are the handled automatically by the host

domain link interface part while all N-Chars are stored in the receiver FIFO for further handling. If

two or more consecutive EOPs/EEPs are received all but the first are discarded.

There are no signals going directly from the transmitter clock domain to the receiver clock domain

and vice versa. All the synchronization is done to the system clock.

Transmitter Clock Domain

Host Clock Domain

Transmitter

Send Time-code

Send FCT

Send NChar

Time-code[7:0]

NChar[8:0]

Figure 6. Schematic of the link interface transmitter.

Receiver Clock Domain

Host Clock Domain

Receiver

Got Time-code

Got FCT

Got NChar

Time-code[7:0]

NChar[7:0]

Figure 7. Schematic of the link interface receiver.

Got EEP

Got EOP

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