refactor coroutine lowering and tasks

src/runtime/runtime_cortexm.go

@@ -40,29 +40,6 @@ func preinit() {
 	}
 }
 
-// calleeSavedRegs is the list of registers that must be saved and restored when
-// switching between tasks. Also see scheduler_cortexm.S that relies on the
-// exact layout of this struct.
-type calleeSavedRegs struct {
-	r4  uintptr
-	r5  uintptr
-	r6  uintptr
-	r7  uintptr
-	r8  uintptr
-	r9  uintptr
-	r10 uintptr
-	r11 uintptr
-}
-
-// prepareStartTask stores fn and args in some callee-saved registers that can
-// then be used by the startTask function (implemented in assembly) to set up
-// the initial stack pointer and initial argument with the pointer to the object
-// with the goroutine start arguments.
-func (r *calleeSavedRegs) prepareStartTask(fn, args uintptr) {
-	r.r4 = fn
-	r.r5 = args
-}
-
 func abort() {
 	// disable all interrupts
 	arm.DisableInterrupts()