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4–62 Chapter 4: Functional Description

Logical Layer Interfaces

RapidIO II MegaCore Function August 2014 Altera Corporation

User Guide

The initial 12 bytes of the NREAD request packet contain header information.

Table 4–37 lists the header fields and their values in this example.

NREAD Response Transaction

In the first clock cycle of the NREAD response on the Avalon-ST pass-through

interface, as shown in Figure 4–23, user logic asserts

gen_rx_hd_ready

and

gen_rx_pd_ready

, and the IP core asserts

gen_rx_hd_valid

and

gen_rx_pd_valid

indicating it is providing valid data on

gen_rx_hd_data

and

gen_rx_pd_data

respectively. The assertion of both the ready signal and the valid signal on each of the

header and payload-data Avalon-ST interfaces makes the current cycle an Avalon-ST

ready cycle for both header and data.

The IP core asserts

gen_rx_pd_startofpacket

to indicate the current cycle is the first

valid data cycle of the packet. In this clock cycle, the IP core also makes the header

and the first 128 bits of payload data available on

gen_rx_hd_data

and

gen_rx_pd_data

, respectively. The 32-byte payload requires two clock cycles. In the

second clock cycle of data transfer, the IP core asserts

gen_rx_pd_endofpacket

indicate this is the final clock cycle of data transfer, and specifies in

gen_rx_pd_empty

that in the current clock cycle, all of the bytes of

gen_rx_pd_data

are valid. Following

the clock cycles in which valid data is available on

gen_rx_pd_data

, the IP core

deasserts

gen_rx_pd_valid

Table 4–37. NREAD Request Transmit Example: RapidIO Header Fields on the gen_tx_data Bus

Field

gen_tx_data

Bits

Value Comment

ackID

[127:122] 6'h00

Value is a don’t care, because it is overwritten by the Physical

layer

ackID

value before the packet is transmitted on the

RapidIO link.

[121] 0 The RapidIO II IP core supports only VC0.

CRF

[120] 0

prio[1:0]

[119:118] 2'b01

tt[1:0]

[117:116] 2'b01 The value of 1 indicates 16-bit device IDs.

ftype[3:0]

[115:112] 4'b0010 The value of 2 indicates a Request Class packet.

destinationId[15:0]

[111:96] 16'hDDDD

sourceId[15:0]

[95:80] 16'hAAAA

ttype[3:0]

[79:76] 4'b0100 The value of 4 indicates an

NREAD

transaction.

size[3:0]

[75:72] 4'b1100

The

size

and

wdptr

values encode the maximum size of the

payload field. In this example, they decode to a value of 32

bytes. For details, refer to Table 4-3 in Part 1: Input/Output

Logical Specification of the RapidIO Interconnect Specification,

Revision 2.2.

transactionID[7:0]

[71:64] 8'hBB

address[28:0]

[63:35]

{28’h7654321,

1’b0}

wdptr

[34] 0 Refer to the comment for

size

xamsbs[1:0]

[33:32] 2’b00

1 2 ... 99 100 101 102 103 104 105 106 107 108 109 ... 217 218

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