rbsexton / gatesim_m0

Gate-level simulation of the Cortex-M0. Requires publicly available verilog from ARM.

Simulating the Cortex-M0 with Verilator

Prerequisites

• ARM Cortex-M0 Designstart files. This project was originally built with AT510-MN-80001-r2p0-00rel0. The default project from ARM includes a few peripherals and loads image.hex into memory at address 0x0.
• image.hex file with your binary for execution. One byte per line, in hex:

80
7a
00
89
00

hexdump -v -e '1/0 "" 1/1 "%02x" 1/0 "\n"' binary.bin 

Running the simuation.

• cd to sim and run make
• From the top level directory, run ./sim/obj_dir/Vcmsdk_mcu. The simulator will ingest the image.hex file and run. It will produce a cmsdk_mcu.vcd file that you can inspect with gtkWave. The distribution includes a basic MPE Forth image.

The ./sim directory contains a makefile to verilate the project into c++ and run it. Setting up and running verilator is way beyond the scope of this document.

Verilator notes

Verilator appears to flatten the design. It doesn't give you easy ways to look at internal signals. The approved way to do that is with functions in verilog.

Memory Map

The default memory map is defined in ./AT510-MN-80001-r2p0-00rel0/systems/cortex_m0_mcu/verilog/cmsdk_mcu_addr_decode.v

• 0x4000:000 APB defined by cmsdk_apb_slave_mux
  • timer 0
  • timer 1
  • dual timer 0
  • :3000 // CommFIFO
  • // uart 0
  • // uart 1
  • // uart 2
  • // not used
  • // watchdog
  • // not used
  • // not used
  • (INCLUDE_APB_TEST_SLAVE), // test slave for validation purpose
  • (APB_EXT_PORT12_ENABLE),
  • (APB_EXT_PORT13_ENABLE),
  • (APB_EXT_PORT14_ENABLE),
  • (APB_EXT_PORT15_ENABLE)
• 0x4001:0000 GPIO0
• 0x4001:1000 GPIO1
• 0x4001:F000 System Control
• 0xF000:0000 System ROM

UART FIFO interface

Encoding/Decoding of UART bits consumes compute and simulation time that isn't necessary. The cosimulation implements the following interface for communication with the host environment.

Base address: 0x4800:0000

  Offsets:
  0x000 Write to host (8-bit)
  0x004 Write to host free bytes 

  0x010 Read from host (8-bit)
  0x014 Read from host available byte count

Revision History

• 2021 Feb 13 First Draft

The default project has a .hex file that you can use as a sample.