Add Linux loader

[shenki]

This privdes just enough firmware to load Linux. The loader is linked to
run from the aliased BRAM address.

It can load a raw kernel (vmlinux.bin) or a wrapper that embeds the
device tree (dtbImage.microwatt).

The printf comes from https://github.com/mpredfearn/simple-printf

1. Build Linux for microwatt
   objcopy -O binary microwatt/vmlinux vmlinux.bin

2. Build a dtb

3. Set MW_DEBUG to point to a copy of mw_debug and type make load to
   load the loader into BRAM.

4. Press 'RESET'

5. Follow the instructions:

   Microwatt Loader (Jun 2 2020 21:31:16)

   Load binaries into SDRAM and select option to start:

   vmlinux.bin and dtb:
   mw_debug -b jtag stop load vmlinux.bin load microwatt.dtb 1000000 start
   press 'l' to start'

   dtbImage.microwatt:
   mw_debug -b jtag stop load dtbImage.microwatt 500000 start
   press 'w' to start'

If you want to test other software, such as MicroPython, you can also
load it to the start of SDRAM and the loader will jump to it with 'l'.

Signed-off-by: Joel Stanley joel@jms.id.au

[ozbenh]

There's a printf along with the small libc in litedram/gen-src/sdram_init. This is similar to the one I put in simple_random. Let's not add yet another one :)

I'm thinking moving a bunch of that stuff to a sw/ directory, we shall see..

[paulusmack]

Joel, were you going to update this? I thought you were going to lose the printf and just use explicit print_string and print_hex calls (to reduce the object code size), and also remove the row of dots being printed.

[shenki]

We can now load Linux directly from flash on the Arty now that Ben's flash controller is implemented.

I can update this so it can be used from the flash if we think that would be useful?

[ozbenh]

On Sun, 2020-06-14 at 20:55 -0700, Joel Stanley wrote: We can now load Linux directly from flash on the Arty now that Ben's flash controller is implemented. I can update this so it can be used from the flash if we think that would be useful?

Ideally we want a loader that can generate the right device-tree for the board based on the board type and syscon setup bits. It can then load a secondary payload from flash, ethernet or serial... In fact, it could also provide a little OPAL blob :-) We'll probably want that for XICS unless we add native ICS support to Linux. Cheers, Ben.