Bare metal ZPU "Hello world"

[offroad]

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;

[Jack Gassett]

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.

[offroad]

Thanks for the hint! I had a quick look, looks good, well documented.

I guess I'd use it for any "real" project.