Altera RapidIO II MegaCore Function - Manual (Page 104)

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 to
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.
VC [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