avr: automatically generate interrupt vectors

targets/avr.S

@@ -1,14 +1,11 @@
-.section .isr
-isr:
-    rjmp reset
-
-.org 0x18 ; WDT
-    rjmp wdt
+; This file provides common code across AVRs that cannot be implemented directly
+; in Go.
+; The reset vector is device-specific and is generated by tools/gen-device-avr.py.
 
 ; Startup code
-.section .reset
-.org 26
-reset:
+.section .text.__vector_RESET
+.global  __vector_RESET
+__vector_RESET:
     clr  r1          ; r1 is expected to be 0 by the C calling convention
 
     ; Set up the stack pointer.
@@ -41,10 +38,21 @@ init_data_end:
     ; need to jump.
 
 
+; This is the default handler for interrupts, if triggered but not defined.
+; Sleep inside so that an accidentally triggered interrupt won't drain the
+; battery of a battery-powered device.
+.section .text.__vector_default
+.global  __vector_default
+__vector_default:
+    sleep
+    rjmp __vector_default
+
+
 ; The only thing this WDT handler really does is disable itself, to get out of
 ; sleep mode.
-.section .text.wdt
-wdt:
+.section .text.__vector_WDT
+.global  __vector_WDT
+__vector_WDT:
     push r16
 
     clr  r16