Update README.

Add license

README.md

@@ -4,6 +4,8 @@ uvm32 is a minimalist, dependency-free virtual machine sandbox designed for micr
 
 On an [STM32L0](https://www.st.com/en/microcontrollers-microprocessors/stm32l0-series.html) (ARM Cortex-M0+) the required footprint is under 4KB flash/1KB RAM.
 
+uvm32 is a RISC-V emulator, wrapped in a management interface and provided with tools to build efficient code to run in it.
+
 ## What is it for?
 
 * As a no-frills alternative to embedded script engines ([Lua](https://www.lua.org/), [Duktape](https://duktape.org/), [MicroPython](https://micropython.org/), etc)
@@ -11,6 +13,25 @@ On an [STM32L0](https://www.st.com/en/microcontrollers-microprocessors/stm32l0-s
 * As a way to allow development in modern systems programming languages where a compiler for the target may not be available ([rust-hello](apps/rust-hello))
 * As a way to [write once, run anywhere](https://en.wikipedia.org/wiki/Write_once,_run_anywhere) and avoid maintaining multiple software variants
 
+## How does it compare to the alternatives?
+
+Many scripting languages and virtual machines are available for embedding in small systems and they all make tradeoffs in different dimensions.
+
+uvm32 aims for:
+
+* Small footprint (suitable for embedded devices, games and apps)
+* Support well-known programming languages for VM code (with high quality dev tools)
+* Ease of integration into existing software
+* Flexibility of paradigm (event driven, polling, multi-processor)
+* Robustness against misbehaving VM code
+
+uvm32 does not aim for:
+
+* Frictionless [FFI](https://en.wikipedia.org/wiki/Foreign_function_interface) (no direct function calls between host and VM code)
+* Maximum possible efficiency
+* The simplest scripting experience for VM code (a develop-compile-run cycle is expected)
+* "Batteries included" libraries to do stdio, networking, etc
+
 ## Features
 
 * Bytecode example apps written in C, Zig, Rust and assembly
@@ -29,7 +50,7 @@ uvm32 is a tiny virtual machine, all of the code is in [uvm32](uvm32).
 
 A minimal example of a host to run code in is at [host-mini](hosts/host-mini).
 
-Everything else is a more advanced host, or a sample application which could be run.
+Everything else is a more advanced host example, or a sample application which could be run in a host.
 
 ## Example
 
@@ -66,10 +87,10 @@ int main(int argc, char *argv[]) {
             case UVM32_EVT_SYSCALL:    // vm has paused to handle UVM32_SYSCALL
                 switch(evt.data.syscall.code) {
                     case UVM32_SYSCALL_PUTC:
-                        printf("%c", uvm32_getval(&vmst, &evt, ARG0));
+                        printf("%c", uvm32_arg_getval(&vmst, &evt, ARG0));
                     break;
                     case UVM32_SYSCALL_PRINTLN: {
-                        const char *str = uvm32_getcstr(&vmst, &evt, ARG0);
+                        const char *str = uvm32_arg_getcstr(&vmst, &evt, ARG0);
                         printf("%s\n", str);
                     } break;
                     case UVM32_SYSCALL_YIELD:
@@ -120,6 +141,8 @@ int main(int argc, char *argv[]) {
 
 ## Quickstart (docker)
 
+The code in [uvm32](uvm32) to build a VM host is very portable and requires only a C compiler. However, many of the examples provided show how to build target code with different languages and tools. A Dockerfile is provided to set up the required environment.
+
     make dockerbuild
     make dockershell
 

uvm32/uvm32.c

@@ -1,3 +1,29 @@
+/*!
+https://github.com/ringtailsoftware/uvm32
+
+MIT License
+
+Copyright (c) 2025 Toby Jaffey <toby@ringtailsoftware.co.uk>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
 #define MINIRV32_IMPLEMENTATION
 #include "uvm32.h"
 

uvm32/uvm32.h

@@ -1,6 +1,3 @@
-#ifndef UVM32_H
-#define UVM32_H 1
-
 /*!
 https://github.com/ringtailsoftware/uvm32
 
@@ -27,6 +24,9 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
+#ifndef UVM32_H
+#define UVM32_H 1
+
 /*! To use uvm32 in an environment without standard library headers, define CUSTOM_STDLIB_H to the name of header providing the equivalent types to stdint.h and stdbool.h */
 #ifndef CUSTOM_STDLIB_H
 #include <stdint.h>