ioreg macro breaks with "wo" field.

[dpc]

Attemtping to use wo in the following case:

      ioregs!(WDOG = {                                                                      
          0x0 => reg16 stctrlh                                                              
          {                                                                                 
              0 => en,                                                                      
              4 => allowupdate                                                              
          },                                                                                

          0xc => reg16 refresh {                                                            
              0..15 => refresh                                                              
              /* breaks the macro too                              
               {                                                                            
                  0xa602 => Seq1,                                                           
                  0xb480 => Seq2,                                                           
               }*/,                                                                         
          },                                                                                

          0xe => reg16 unlock {                                                             
              0..15 => unlock: wo, /* the issue is about this */                                                         
              /*breaks the macro too                          
              {                                                                             
                  0xc520 => Seq1,                                                           
                  0xd928 => Seq2,                                                           
              }*/,                                                                          
          },                                                                                

      }) 

results in:

[futex:zinc]$ make
rake PLATFORM=k20 build_all
rustc --opt-level 2 -Z no-landing-pads --cfg mcu_k20 --cfg arch_cortex_m4 --target thumbv7em-linux-eabi -Ctarget-cpu=cortex-m4 -C relocation_model=static  -Z lto  --emit obj  -L /home/dpc/lab/rust/zinc/build  -o /home/dpc/lab/rust/zinc/build/intermediate/blink_k20/app_blink_k20.o  /home/dpc/lab/rust/zinc/apps/app_blink_k20.rs 
<quote expansion>:1:1: 1:18 error: use of undeclared type name `WDOG_unlock_Get`
<quote expansion>:1 name_290,ctxt_0
                    ^~~~~~~~~~~~~~~~~
/home/dpc/lab/rust/zinc/apps/app_blink_k20.rs:1:1: 147:1 note: in expansion of ioregs!
/home/dpc/lab/rust/zinc/apps/app_blink_k20.rs:37:5: 62:7 note: expansion site
<quote expansion>:1:1: 62:7 error: failed to resolve. Use of undeclared module `WDOG_unlock_Get`
<quote expansion>:1 name_290,ctxt_0
error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'index out of bounds: the len is 1 but the index is 1', /home/dpc/opt/src/rust/src/libsyntax/lib.rs:1

[dpc]

I guess the problem is that the field is the only field in the whole register.

Also, I find it a problem, that I can't mark whole register as a "wo". I'm working on a case in which watchdog needs two quick consecutive writes, and ioreg macro is generating sequence of read+write, for both accesses which breaks. I'd like to be sure that for register that are wo as a whole, no write code is generated.

It would be nice if whole register could be treated as a one big bit-field.

Pinging @bgamari, because it seems he could help me. :)

[bharrisau]

No, the problem is that there is a get() method here (https://github.com/hackndev/zinc/blob/master/ioreg/builder/accessors.rs#L37) that returns the struct defined here (https://github.com/hackndev/zinc/blob/master/ioreg/builder/getter.rs#L45).

But the first part is always run, and the second isn't run when everything is wo. The following code should be added to accessors.rs

if fields.iter().any(|f| f.access != node::WriteOnly) {
  let item = build_get_fn(self.cx, path, reg);
  self.builder.push_item(item);
}

I won't have time to do this up as a PR - @dpc do you think you could give it a go?

[bharrisau]

And a test for this case would be good too.

[dpc]

Syntax is passing with the above fix. I need to get rid of unnecessary read, but I'll work on this on #140.

[bgamari]

@dpc I think bb46d6e in #141 should fix the unnecessary read.