Arty S7 OpenOCD Support

[cr1901]

This PR does two things:

1. Fixes a typo that prevented the import from nmigen_boards.arty_s7 import * from working properly.
2. Adds support for the openocd programmer for the Arty S7 board.

I kept in mind your comments re: OpenOCD and programmers in general when writing this PR. So perhaps consider it a litmus test to supporting more than one programmer in nmigen :):

I looked at the openocd invocations currently in nmigen-boards. All of them are different, pretty significantly so.

Indeed, all the openocd invocations are different, and this one's no exception. One difference is that I use the upstream board config file since it's available already (I committed it in mid 2018). Another difference is that I support both JTAG programming and flashing via a proxy.

We can just decide on what to do here. For example, we can decide that on every board with multiple ways to program it, toolchain_program takes a programmer="" keyword argument.

I went ahead and used this suggestion as-is.

toolchain_program should be configurable enough, and just enough, to cover the most typical use cases.

In addition, I added a flash keyword argument that lets the user choose between JTAG programming and flashing a bitstream. JTAG programming is noticeably faster, shortening the already long "write, compile, program" feedback loop. Hopefully at some point Vivado's time can be shaved off too :). Therefore I think this is a reasonable keyword argument to add that will cover most use cases. I don't know if vivado's programmer has an equivalent.

[whitequark]

Unfortunately this ignores the flash argument if Vivado is chosen as the programmer. At the very least it must assert, but ideally it should actually implement that.

[cr1901]

cc: @Fatsie Do you have any experience with programming flash via Vivado? It looks like the program_hw_cfgmem command (page 977) can do the trick, but seeing as Vivado is remote for me, I can't really test this.

[Fatsie]

@cr1901 I have minimal experience with Vivado; for the script I just looked up some commands and fiddled until the script did what it should do. You should be able to do the same unless you don't have Vivado installed.

[Fatsie]

Also apologize for being terse; I am busy with total different things ATM and I don't expect to look at this deeper in the near future.

[cr1901]

You should be able to do the same unless you don't have Vivado installed.

I already said I don't have Vivado installed.

Anyways, @whitequark, can I please assert on this for now? I got someone to help test remotely while I coded a TCL script, but I just cannot get flash programming to work with Vivado. This is the closest I came up with:

open_hw_manager
connect_hw_server
open_hw_target
current_hw_device [lindex [get_hw_devices] 0]
set cfgMem [create_hw_cfgmem -hw_device [current_hw_device] s25fl128sxxxxxx0-spi-x1_x2_x4]
set_property PROGRAM.FILES top-norgb.bin $cfgMem
set_property PROGRAM.ADDRESS_RANGE {use_file} $cfgMem
set_property PROGRAM.BLANK_CHECK 1 $cfgMem
set_property PROGRAM.ERASE 1 $cfgMem
set_property PROGRAM.CFG_PROGRAM 1 $cfgMem
set_property PROGRAM.VERIFY 1 $cfgMem
program_hw_cfgmem $cfgMem

which bombs with:

ERROR: [Labtools 27-3347] Flash Programming Unsuccessful: Failure to set flash parameters.
ERROR: [Common 17-39] 'program_hw_cfgmem' failed due to earlier errors.

I have no idea what Vivado is complaining about; this is the correct flash, according to the Digilent manual. My ability to test is limited; I want someone else to add this functionality.

[whitequark]

Anyways, @whitequark, can I please assert on this for now?

Like I said, that's the bare minimum, so you can do that.

[whitequark]

Something like this would be nicer:

Suggested change

	assert not flash
	assert not flash, "Flash programming is not supported with Vivado yet"

[cr1901]

@whitequark I had another day where someone could help remotely; this time, I got Flash programming working with the caveat that the user needs to manually reset/power-cycle the board. This appears to be a limitation of the Vivado TCL API, as noted in a comment.

[whitequark]

Great work, and thanks for getting Vivado flashing done; this will definitely be useful for other boards in the future.