TM4C1294NCPDT: Add external flash

Hi Deepak,

  You can connect external serial flash through SPI interface. You can also use EPI module to interface with external memories like SDRAM, SRAM and flash and run code from external memory.  Please also refer to this TI reference design that will provide some guidance. https://www.ti.com/reference-designs/index.html#search?keyword=tm4c129

External Peripheral Interface (EPI)
The External Peripheral Interface is a high-speed parallel bus for external peripherals or memory.
It has several modes of operation to interface gluelessly to many types of external devices. The
External Peripheral Interface is similar to a standard microprocessor address/data bus, except that
it must typically be connected to just one type of external device. Enhanced capabilities include
μDMA support, clocking control and support for external FIFO buffers.
The EPI has the following features:
■ 8/16/32-bit dedicated parallel bus for external peripherals and memory
■ Memory interface supports contiguous memory access independent of data bus width, thus
enabling code execution directly from SDRAM, SRAM and Flash memory
■ Blocking and non-blocking reads
■ Separates processor from timing details through use of an internal write FIFO
■ Efficient transfers using Micro Direct Memory Access Controller (μDMA)
– Separate channels for read and write
– Read channel request asserted by programmable levels on the internal Non-Blocking Read
FIFO (NBRFIFO)
– Write channel request asserted by empty on the internal Write FIFO (WFIFO)