avr: automatically generate interrupt vectors

.gitignore

@@ -2,6 +2,7 @@ build
 docs/_build
 src/device/avr/*.go
 src/device/avr/*.ld
+src/device/avr/*.s
 src/device/nrf/*.go
 src/device/nrf/*.s
 src/device/stm32/*.go

targets/arduino.json

@@ -1,8 +1,8 @@
 {
 	"llvm-target": "avr-atmel-none",
-	"build-tags": ["arduino", "atmega328p", "atmega", "avr8", "avr", "js", "wasm"],
+	"build-tags": ["arduino", "atmega328p", "atmega", "avr5", "avr", "js", "wasm"],
 	"linker": "avr-gcc",
-	"pre-link-args": ["-nostartfiles", "-T", "targets/avr.ld", "-Wl,--gc-sections", "targets/avr.S"],
+	"pre-link-args": ["-nostartfiles", "-mmcu=avr5", "-T", "targets/avr.ld", "-Wl,--gc-sections", "targets/avr.S", "src/device/avr/atmega328p.s"],
 	"objcopy": "avr-objcopy",
 	"flash": "avrdude -c arduino -p atmega328p -P {port} -U flash:w:{hex}"
 }

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

targets/avr.ld

@@ -12,8 +12,8 @@ SECTIONS
 {
     .text :
     {
-        KEEP(*(.isr))
-        KEEP(*(.reset))
+        KEEP(*(.vectors))
+        KEEP(*(.text.__vector_RESET))
         KEEP(*(.text.main)) /* main must follow the reset handler */
         *(.text.*)
         *(.rodata)

tools/gen-device-avr.py

@@ -201,6 +201,42 @@ const (
                         out.write('\n')
         out.write(')\n')
 
+def writeAsm(outdir, device):
+    # The interrupt vector, which is hard to write directly in Go.
+    out = open(outdir + '/' + device.metadata['nameLower'] + '.s', 'w')
+    out.write('''\
+; Automatically generated file. DO NOT EDIT.
+; Generated by gen-device-avr.py from {file}, see {descriptorSource}
+
+; Avoid the need for repeated .weak and .set instructions.
+.macro IRQ handler
+    .weak  \\handler
+    .set   \\handler, __vector_default
+.endm
+
+; The interrupt vector of this device. Must be placed at address 0 by the linker.
+.section .vectors
+.global  __vectors
+'''.format(**device.metadata))
+    num = 0
+    for intr in device.interrupts:
+        if intr['index'] < num:
+            # Some devices have duplicate interrupts, probably for historical
+            # reasons.
+            continue
+        while intr['index'] > num:
+            out.write('    jmp __vector_default\n')
+            num += 1
+        num += 1
+        out.write('    jmp __vector_{name}\n'.format(**intr))
+
+    out.write('''
+    ; Define default implementations for interrupts, redirecting to
+    ; __vector_default when not implemented.
+''')
+    for intr in device.interrupts:
+        out.write('    IRQ __vector_{name}\n'.format(**intr))
+
 def writeLD(outdir, device):
     # Variables for the linker script.
     out = open(outdir + '/' + device.metadata['nameLower'] + '.ld', 'w')
@@ -220,6 +256,7 @@ def generate(indir, outdir):
         print(filepath)
         device = readATDF(filepath)
         writeGo(outdir, device)
+        writeAsm(outdir, device)
         writeLD(outdir, device)