Altera HyperTransport MegaCore Function - Manual (Page 43)

Chapter 3: Specifications 3–17
HyperTransport MegaCore Function Specification
© November 2009 Altera Corporation HyperTransport MegaCore Function User Guide
Preliminary
Rx Command/Data Buffer Interfaces
Each HT virtual channel has one Rx command/data interface. These interfaces are
slave source Atlantic interfaces, allowing streaming packets in an easy-to-use
interface.
Rx Command/Data Buffer Interface Signals
Table 3–5 describes the Rx buffer interface signals. Each of these signals has one of the
following three types:
■ Rx response interface (HT MegaCore function signal names prefixed with RxR)
■ Rx posted interface (HT MegaCore function signal names prefixed with RxP)
■ Rx non-posted interface (HT MegaCore function signal names prefixed with
RxNp)
Because each channel uses similar interface signals, they are only described once. Any
channels that have specific differences are noted in
Table 3–5 .
Table 3–5. Rx Command/Data Buffer Interface Signals (Part 1 of 2)
Signal Name Direction Description
Dat_o[63:0] Output Data bus. This 64-bit bus contains the actual HT command/data information received
from the HT link. This bus has the following constraints:
■ Data received from the link is organized in Atlantic packets.
■ Data is transferred in a little endian format (first byte is in Dat_o[7:0] ).
■ The Atlantic packet on the Rx interface contains a command phase followed by zero,
one, or more data phases.
■ During the command phase, Sop_o is asserted to indicate the start of packet. That is,
Sop indicates the start of an Atlantic packet and indicates that Dat_o[63:0]
contains the HT command.
■ The data presented on Dat_o[63:0] is presented with the bytes in the order they
are received from the HT link. Therefore, the first byte received from the HT link in a
command packet is provided on
Dat_o[7:0] .
■ If the command has no associated data, such as a non-posted read request or
TgtDone response packet, Sop_o and Eop_o are asserted at the same time.
■ You can decode the command bits to determine whether there is data associated with
the command (and how much) while
Sop_o is asserted.
Mty_o[2:0] Output Data byte empty. This bus indicates which bytes are invalid on Dat_o[63:0] . Because
HT packets are DWORD aligned, only two valid encodings are used by the
HyperTransport MegaCore function. The following
Mty_o signal values are possible:
■ Mty_o = '000' , all bytes on Dat_o[63:0] are valid.
■ Mty_o = '100' , Dat_o[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_o 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_o is
asserted, Dat_o[63:32] is implicitly invalid. The first data bytes are placed on the
Dat_o bus the cycle after Sop_i . If the 32-bit command does not have data, the
Mty_o signals are set to '100', and Eop_o and Sop_o are asserted.