get rid of any stdlib code, declare main as naked and do avr initialization...

get rid of any stdlib code, declare main as naked and do avr initialization (stack, etc.) on our own.

Makefile

@@ -4,18 +4,12 @@ STRIP=avr-strip
 
 CPPFLAGS += -mmcu=atmega8 -DF_CPU=8000000UL 
 CFLAGS += -std=gnu99 -Os -g -Wall -W
-LDFLAGS += $(CFLAGS)
-
-#
-# in order to get rid of .bss and .data initialization code,
-# don't link in stdlibs but just crts8515 (for stack initialization)
-#
-LDFLAGS += -nostdlib `avr-gcc -print-file-name=crts8515.o`
+LDFLAGS += $(CFLAGS) -nostdlib
 
 all: funkloader.hex
 
-funkloader: funkloader.o rfm12_trans.o rfm12_wait_read.o exit.o \
-	funkloader_tx_reply.o
+funkloader: funkloader.o rfm12_trans.o rfm12_wait_read.o \
+	funkloader_tx_reply.o memconfig.o
 	$(CC) -o $@ $(LDFLAGS) $^
 
 clean:

funkloader.c

@@ -29,6 +29,7 @@
 #include "pinconfig.h"
 
 #define noinline __attribute__((noinline))
+#define naked    __attribute__((naked))
 
 extern unsigned short rfm12_trans (unsigned short);
 extern unsigned char  rfm12_wait_read (void);
@@ -159,7 +160,8 @@ crc_check (void)
   return crc_chk;
 }
 
-int
+
+naked int
 main (void)
 {
   spi_init ();
@@ -188,4 +190,13 @@ main (void)
       funkloader_tx_reply ();
       rfm12_trans(0x8208);	/* TX off */
     }
+  
+
+  /* jump into application now */
+
+  GICR = _BV(IVCE);	        /* prepare ivec change */
+  GICR = 0x00;                  /* change ivec */
+  
+  void (*jump_to_application)(void) = 0;
+  jump_to_application();
 }

exit.S → memconfig.c

@@ -19,22 +19,23 @@
 #define  __SFR_OFFSET 0
 #include <avr/io.h>
 
-#include "pinconfig.h"
 
-	.file	"exit.S"
-	.text
-	
-.global exit
-	.type	exit, @function
-exit:
+void __attribute__ ((naked, section(".init3"))) init_avr (void);
 
-	;; change interrupt vector to application
-	ldi	r24, (1 << IVCE)
-	out	GICR, r24
+void 
+init_avr (void)
+{
+  /* clear zero-register */
+  __asm volatile ("eor r1, r1 \n\t");
 
-	ldi	r30, 0
-	out	GICR, r30
+  /* clear sreg */
+  __asm volatile ("out __SREG__, r1 \n\t");
 
-	;; jump to application
-	ldi	r31, 0		; Z = 0x0000!
-	icall
+  /* initialize stack pointer */
+  __asm volatile ("ldi r28, lo8(%0) \n\t"
+		  "ldi r29, hi8(%0) \n\t"
+		  "out __SP_H__, r29     \n\t"
+		  "out __SP_L__, r28     \n\t"
+		  :
+		  : "i" (RAMEND));
+}