I came across an outdated hello world tutorial for Migen which really confuses me.
In this tutorial, the author describes how CSRs (e.g.
CSRStorage) can be accessed from the host. In the example, CSRs are directly imported from Migen. Since CSRs are not longer available in Migen, I guess that Migen was split into Migen and MiSoC and that CSRs were moved to MiSoC.
What really puzzles me is that the author shows how CSRs can be accessed from the host. I first assumed that the host referred to SoC running on the FPGA but the example is written in Python:
@command('hello', ('v', int16))
def hello(dev, v):
print("Hello returns %02x" % dev.regs.hello_output.rd())
Unless the SoC is running Linux, I think that the host machine refers to the machine connected to the FPGA. How is this possible? What interface does it use between the host and the FPGA?