move to xargo and nightly

Author: pftbest

Cargo.toml

@@ -10,5 +10,4 @@ volatile-register = "0.1.2"
 debug = true
 
 [profile.release]
-debug = true
 lto = true

Makefile

@@ -1,7 +1,8 @@
-TARGET = target/msp430g2553/release/msp
+DEVICE = msp430g2553
+TARGET = target/$(DEVICE)/release/msp
 
 all:
-	RUSTFLAGS="--sysroot sysroot" cargo build --release --target=msp430g2553
+	xargo build --release --target $(DEVICE)
 	msp430-elf-objdump -Cd $(TARGET) > $(TARGET).lst
 	msp430-elf-size $(TARGET)
 

README.md

@@ -4,16 +4,60 @@
 
 ## Compiling
 
-Unfortunately, it is not possible to build this project without patches
-form [#38286](https://github.com/rust-lang/rust/pull/38286) and [#38240](https://github.com/rust-lang/rust/pull/38240), so we need to wait until they land in nightly.
+This project can be compiled using nightly rust and [xargo](https://github.com/japaric/xargo).
+
+Tested using version `1.15.0-nightly (8f02c429a 2016-12-15)`.
+
+Steps:
+* First, install msp430-elf-gcc compiler, and make sure it is in your $PATH.
+ You can get it from [here](http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/MSPGCC/latest/index_FDS.html). 
+* Install nightly rust
+
+  `$ rustup default nightly`
+* Install xargo
+
+  `$ cargo install xargo`
+* Build the project using
+
+  `$ make`
+
+* or you can build it using xargo directly (if you don't like `make`)
+
+  `$ xargo build --release --target msp430g2553`
+
+* Flash the firmware using `mspdebug`
+
+  `$ make prog`
 
 ## How it works
 
-* First issue you may run into is incompatibility between MSP430 and MSP430X. When `rustc` compiles code it does not pass `-mmcu` flag to the gcc, so gcc choses default ISA. For `msp430-elf-gcc` it is MSP430X, and it is not what you want for `msp430g2553` MCU. To work around this, you should create a *shim* compiler like [`msp-gcc.sh`](https://github.com/pftbest/rust_on_msp/blob/master/msp-gcc.sh) that will pass the necessary flags to gcc.
+* One of the issues you may run into is incompatibility between MSP430 and
+  MSP430X. When `rustc` compiles code it does not pass `-mmcu` flag to the gcc,
+  so gcc choses default ISA. For `msp430-elf-gcc` it is MSP430X, and it is not 
+  what you want for `msp430g2553` MCU. To work around this, you should create 
+  a *shim* compiler like [`msp-gcc.sh`](https://github.com/pftbest/rust_on_msp/blob/master/msp-gcc.sh)
+  that will pass the necessary flags to gcc.
+
+* This project is does not use default startup code from gcc, so a reset handler should be defined like this:
+  ```rust
+  #[no_mangle]
+  #[link_section = "__interrupt_vector_reset"]
+  pub static RESET_VECTOR: unsafe extern "C" fn() -> ! = main;
+  ```
+  RESET_VECTOR is just a function pointer that gets placed inside a special section called
+  `__interrupt_vector_reset` and is pointing to `main` function, so it will be called on reset.
+  Other interrupts may be defined the same way for example `__interrupt_vector_timer0_a0`, but it
+  is not possible to use interrupts yet (other than reset), because rust doesn't have a special 
+  calling convention for MSP430 interrupts.
 
-* Second issue is that rust compiler will pass the `-nodefaultlibs` flag to gcc by default, and for some reason (unknown to me) gcc will fail to emit startup code with this flag present. To fix this you should set `"no-default-libraries": false` option in json file for your target.
+## Proting to other boards and MCUs
 
-* Third issue, well it is not an issue, just an inconvenience. I was using a custom rust compiler with patches mentioned above, and found out that `xargo` does not support custom compilers. So I had two options: either add `libcore` crate sources as a dependency in my `Cargo.toml`, or to compile `libcore` separately and put its binary into `sysroot`. I chose the latter case, because it allows me to use other crates like `volatile-register` without changing their source code.
+To run this code on the other boards and MCUs, you need to change it in few places:
+* Get a linker script for your MCU from msp430-elf-gcc include directory, and place it
+  inside `ldscripts` folder.
+* Rename `msp430g2553.json` and modify it to point to the right liker script from step 1
+* Modify `msp-gcc.sh` so it would pass the right mcu name to the gcc.
+* Modify `DEVICE` variable inside a Makefile.
 
 ## Board
 

msp430g2553.ld renamed to ldscripts/msp430g2553.ld

@@ -5,12 +5,16 @@
   "features": "-ext",
   "llvm-target": "msp430",
   "max-atomic-width": 0,
-  "no-default-libraries": false,
   "no-integrated-as": true,
   "os": "none",
   "panic-strategy": "abort",
   "relocation-model": "static",
   "target-endian": "little",
   "target-pointer-width": "16",
-  "linker": "./msp-gcc.sh"
+  "linker": "./msp-gcc.sh",
+  "post-link-args": [
+    "-Lldscripts",
+    "-Tmsp430g2553.ld",
+    "-nostartfiles"
+  ]
 }

msp430g2553_symbols.ld renamed to ldscripts/msp430g2553_symbols.ld

@@ -12,6 +12,20 @@ extern "C" {
     static mut P1OUT: RW<u8>;
 }
 
+#[no_mangle]
+#[link_section = "__interrupt_vector_reset"]
+pub static RESET_VECTOR: unsafe extern "C" fn() -> ! = main;
+
+pub unsafe extern "C" fn main() -> ! {
+    WDTCTL.write(0x5A00 + 0x80);
+    P1DIR.write(0b0100_0001);
+    P1OUT.write(0x01);
+    loop {
+        P1OUT.modify(|x| !x);
+        delay(40000);
+    }
+}
+
 #[allow(unused_variables)]
 #[allow(unused_assignments)]
 fn delay(mut n: u16) {
@@ -23,19 +37,7 @@ fn delay(mut n: u16) {
 }
 
 #[no_mangle]
-pub extern "C" fn main() {
-    unsafe {
-        WDTCTL.write(0x5A00 + 0x80);
-        P1DIR.write(0b0100_0001);
-        P1OUT.write(0x01);
-    }
-    loop {
-        unsafe {
-            P1OUT.modify(|x| {!x});
-        }
-        delay(40000);
-    }
-}
-
 #[lang = "panic_fmt"]
-extern "C" fn panic_fmt() {}
+pub extern "C" fn panic_fmt() -> ! {
+    loop {}
+}