Baud
Rate
Control
(Clock)
AHB
Bus
Interface
With
DMA
Wide
Parallel
Interface
Host Bus
SDRAM
General
Parallel
GPIO
AHB
EPI 43:0
NBRFIFO
8 x32 bits
WFIFO
4 x32 bits
EPI Block Diagram
1229
SPRUHE8E – October 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
External Peripheral Interface (EPI)
–
1 to 32 bits, FIFOed with speed control
–
Useful for custom peripherals or for digital data acquisition and actuator controls
17.2 EPI Block Diagram
provides a block diagram of the EPI module.
Figure 17-1. EPI Block Diagram
17.3 Functional Description
The EPI controller provides a glueless, programmable interface to a variety of common external
peripherals such as SDRAM x16, Host Bus x8 and x16 devices, RAM, NOR Flash memory, CPLDs and
FPGAs. In addition, the EPI controller provides custom GPIO that can use a FIFO with speed control by
using either the internal write FIFO (WFIFO) or the non-blocking read FIFO (NBRFIFO). The WFIFO can
hold four words of data that are written to the external interface at the rate controlled by the EPI Main
Baud Rate (EPIBAUD) registers. The NBRFIFO can hold eight words of data and samples at the rate
controlled by the EPIBAUD register. The EPI controller provides predictable operation and thus has an
advantage over regular GPIO which has more variable timing due to on-chip bus arbitration and delays
across bus bridges. Blocking reads stall the CPU until the transaction completes. Non-blocking reads are
performed in the background and allow the processor to continue operation. In addition, write data can
also be stored in the WFIFO to allow multiple writes with no stalls.
NOTE:
Both the WTAV bit field in the EPIWFIFOCNT register and the WBUSY bit in the EPISTAT
register must be polled to determine if there is a current write transaction from the WFIFO. If
both of these bits are clear, then a new bus access may begin.