LFSC datasheet(41/237 Pages) LATTICE

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2-37

Architecture

Lattice Semiconductor

LatticeSC/M Family Data Sheet

Figure 2-31. LatticeSC System Bus Interfaces

Several interfaces exist between the System Bus and other FPGA elements. The MPI interface acts as a bridge

between the external microprocessor bus and System Bus. The MPI may work in an independent clock domain

from the System Bus if the System Bus clock is not sourced from the external microprocessor clock. Pipelined

operation allows high-speed memory interface to the EBR and peripheral access without the requirement for addi-

tional cycles on the bus. Burst transfers allow optimal use of the memory interface by giving advance information of

the nature of the transfers.

Details for the majority of the peripherals can be found in the associated technical documentation, see details at

the end of this data sheet. Additional details of the MPI are provided below.

Microprocessor Interface (MPI)

The LatticeSC family devices have a dedicated synchronous MPI function block. The MPI is programmable to oper-

ate with PowerPC/PowerQUICC MPC860/MPC8260 series microprocessors. The MPI implements an 8-, 16-, or

32-bit interface with 1-bit, 2-bit, or 4-bit parity to the host processor (PowerPC) that can be used for conﬁguration

and read-back of the FPGA as well as for user-deﬁned data processing and general monitoring of FPGA functions.

The control portion of the MPI is available following power-up of the FPGA if the mode pins specify MPI mode, even

if the FPGA is not yet conﬁgured. The width of the data port is selectable among 8-, 16-, or 32-bit and the parity bus

can be 1-, 2-, or 4-bit. In conﬁguration mode the data and parity bus width are related to the state of the M[0:3]

mode pins. For post-conﬁguration use, the MPI must be included in the conﬁguration bit stream by using an MPI

library element in your design from the ispLEVER primitive library, or by setting the bit of the MPI conﬁguration con-

trol register prior to the start of conﬁguration. The user can also enable and disable the parity bus through the con-

ﬁguration bit stream. These pads can be used as general I/O when they are not needed for MPI use.

The MPI block also provides the capability to interface directly to the FPGA fabric with a databus after conﬁgura-

tion.The bus protocol is still handled by the MPI block but the direct FPGA access allows high-speed block data

transfers such as DMA transactions. Figure 2-32 shows one of the ways a PowerPC is connected to MPI.

DFA

(Direct Access

from MPI)

SMI

(PLL, DLL,

USER LOGIC)

STATUS and

CONFIG

(SYS REG)

CONFIG

(MASTER)

System Bus

USI

(SLAVE)

UMI

(MASTER)

EBR INIT

(WRITE)

MPI

(MASTER)

PCS (LEFT, RIGHT

and INTER-QUAD)

(SLAVE)

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