offroad

Bare metal ZPU "Hello world"

Recommended Posts

Hi,

 

here is an example project (download) that shows how to

  • create a ZPU on a Papilio Pro board
  • compile a C program (gcc)
  • insert the bit stream
  • simple IO (no wishbone bus)
  • integrate the ZPU into Verilog (rewriting the top-level file in VHDL would be trivial.

Anything that's not essential is removed.

For those who haven't yet met one: The ZPU is a tiny microcontroller with a GCC development environment.

 

Most of the code is borrowed from here.

My contribution is to remove stuff to the point where it barely works - it's still complicated enough. zpu_config.vhd was largely rewritten.

There is one clock input, one LED output, and that's all.

 

Cygwin is required to compile C code. The ZPU compiler binaries are included.

 

Step 1: Check that the pre-built binary works

  • Start Papilio loader;
  • select "uploadme.bit" as "Target .bit file".
  • "Write to: FPGA" is fastest

On completion, the LED should blink slowly

 

Step 2: Compile your own binary

  • Edit c-code/main2.c (there are 3 blink variants to choose from, edit #if... /#elif)
  • Run build.sh. You may have to edit it once and set correct paths
  • If successful, the new binary is copied to the bitstream
  • repeat Step 1 and the LED should blink differently.

Step 3: Rebuild the project (Xilinx ISE 14.7 web edition)

  • For example, in src/zpu_config.vhd, change
    constant maxAddrBitIncIO    : integer := 15;
    to 16.
  • Now the C code won't control the LED anymore, until it is changed from
    volatile unsigned int* io = (unsigned int*)0x00008000;
    to
    volatile unsigned int* io = (unsigned int*)0x00010000;

Share this post


Link to post
Share on other sites

offroad, thank you for putting this example project together.

 

I just wanted to make sure that you have seen Alvaro Lopes' ZPUino? Its a ZPU derivative for the Papilio that is also based on ZPU.

 

Jack.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now