u-boot/board/imgtec/xilfpga

/*
 * Copyright (C) 2016, Imagination Technologies Ltd.
 *
 * Zubair Lutfullah Kakakhel, Zubair.Kakakhel@imgtec.com
 */

MIPSfpga
=======================================

MIPSfpga is an FPGA based development platform by Imagination Technologies
As we are dealing with a MIPS core instantiated on an FPGA, specifications
are fluid and can be varied in RTL.

The example project provided by IMGTEC runs on the Nexys4DDR board by
Digilent powered by the ARTIX-7 FPGA by Xilinx. Relevant details about
the example project and the Nexys4DDR board:

- microAptiv UP core m14Kc
- 50MHz clock speed
- 128Mbyte DDR RAM	at 0x0000_0000
- 8Kbyte RAM		at 0x1000_0000
- axi_intc		at 0x1020_0000
- axi_uart16550		at 0x1040_0000
- axi_gpio		at 0x1060_0000
- axi_i2c		at 0x10A0_0000
- custom_gpio		at 0x10C0_0000
- axi_ethernetlite	at 0x10E0_0000
- 8Kbyte BootRAM	at 0x1FC0_0000
- 16Mbyte QPI		at 0x1D00_0000

Boot protocol:
--------------

The BootRAM is a writeable "RAM" in FPGA at 0x1FC0_0000.
This is for easy reprogrammibility via JTAG.

DDR initialization is already handled by a HW IP block.

When the example project bitstream is loaded, the cpu_reset button
needs to be pressed.

The bootram initializes the cache and axi_uart
Then checks if there is anything non 0xffff_ffff at location 0x1D40_0000

If there is, then that is considered as u-boot. u-boot is copied from
0x1D40_0000 to memory and the bootram jumps into u-boot code.

At this point, the board is ready to load the Linux kernel + buildroot initramfs

This can be done in multiple ways:

1- JTAG load the binary and jump into it.
2- Load kernel stored in the QSPI flash at 0x1D80_0000
3- Load uImage via tftp. Ethernet works in u-boot.
   e.g. env set server ip 192.168.154.45; dhcp uImage; bootm