compiler: add support for parameters to inline assembly

docs/microcontrollers.rst

@@ -113,8 +113,25 @@ The device-specific packages like ``device/avr`` and ``device/arm`` provide
 
     arm.Asm("wfi")
 
-There is no support yet for inline assembly that takes (register) parameters or
-returns a value.
+You can also pass parameters to the inline assembly::
+
+    var result int32
+    arm.AsmFull(`
+        lsls  {value}, #1
+        str   {value}, {result}
+    `, map[string]interface{}{
+        "value":  42,
+        "result": &result,
+    })
+    println("result:", result)
+
+In general, types are autodetected. That is, integer types are passed as raw
+registers and pointer types are passed as memory locations. This means you can't
+easily do pointer arithmetic. To do that, convert a pointer value to a
+``uintptr``.
+
+Inline assembly support is expected to change in the future and may change in a
+backwards-incompatible manner.
 
 
 Harvard architectures (AVR)