Altera HyperTransport MegaCore Function Bedienungsanleitung PDF herunterladen (Seite 49)

Chapter 3: Specifications 3–23

HyperTransport MegaCore Function Specification

Preliminary

Table 3–7. Tx Command/Data Buffer Interface Signals (Part 1 of 2)

Signal Name Direction Description

Dat_i[63:0] Input Data bus. This 64-bit input bus carries the data input to the command/data buffer. Data is

loaded in little endian format (least significant byte is loaded first on Dat_i[7:0]).

Mty_i[2:0] Input Data byte empty. This bus indicates which bytes are invalid on Dat_i[63:0]. Because

HT packets are DWORD aligned, there are only two valid encodings used by the

HyperTransport MegaCore function. The following Mty_i signal values are acceptable:

Mty_i = ‘000’, all bytes on Dat_i[63:0] are valid.

Mty_i = ‘100’, Dat_i[63:32] are invalid.

Invalid bytes can only be on the last word of a packet. It is illegal to have a non-zero value

for the Mty_i signals for words other than the last word of the packet, even for 32-bit

commands that have data, such as a read response. In this case, when Sop_i is asserted,

Dat_i[63:32] is implicitly invalid. The first data bytes are placed on the Dat_i bus

the cycle after the Sop_i.

If the 32-bit command does not have data, the Mty_i signals should be set to ‘100’ and

Eop_i and Sop_i should be asserted.

Sop_i Input Start of packet. This signal must be high at the start of the packet. Start of packet is always

loaded with least significant bytes loaded first. The first 64-bit word of a packet must

always be the command. If the command is only 32 bits, it must be loaded on

Dat[31:0] and the buffer ignores Dat_i[63:32].

Eop_i Input End of packet. This signal indicates the end of packet. Eop_i must be high at the end of

the packet. When this signal is high, the Mty_i signals can indicate that Dat_i[63:32]

are invalid.

WrRjct_o Output Write reject. This signal indicates that the local-side application’s attempted write into the

buffer has been rejected due to an error. The following errors cause the WrRjct_o signal

to be asserted:

■ A write is attempted while Dav_o is low.

■ A write of the first word of a packet (command) was performed without Sop_i

asserted.

■ A write is attempted that has more than 9 valid cycles. The maximum transfer is the HT

command packet followed by a 64 byte HT data packet.

If any of the above errors are detected, the write is rejected; the internal address counters

and buffer status registers are reset to indicate that there were no writes after the last

successful packet. Packets that were written into the buffer before the packet with the error

are not affected and are transmitted to the link as usual.

The WrRjct_o signal is intended for use as a debugging signal for simulation and early

prototypes.

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Altera HyperTransport MegaCore Function Bedienungsanleitung Seite 49