avrboot/lowlevel.c

//
//  Low-level bootloader routines to replace "assembly.s90"
//  from the original ATMEL Butterfly bootloader code
//  which are not included in avr-libc's boot.h by the 
//  time of writing this.
//
//  3/2004 Martin Thomas, Kaiserslautern, Germany
//

#include "lowlevel.h"

unsigned int read_program_memory(unsigned int adr, unsigned char param)
// to read lockbits give param=0x09, if param!=0 it is written to SPMCSR
// this is a "translation" from the original code to gcc-inline-assembler
{
	unsigned int retval;
	
	asm volatile
	(
		"movw r30, %3\n\t"
		"sbrc %2,0x00\n\t"
		"sts %0, %2\n\t"
		#ifdef LARGE_MEMORY  // If large memory (>64K) ELPM is needed to use RAMPZ
		"elpm\n\t"           // read LSB
		#else
		"lpm\n\t"            // R0 is now the LSB of the return value
		#endif
		"mov %A1,r0\n\t"
		"inc r30\n\t"
		#ifdef LARGE_MEMORY  // If large memory (>64K) ELPM is needed to use RAMPZ        
		"elpm\n\t"           // read MSB
		#else
		"lpm\n\t"            // R0 is now the MSB of the return value
		#endif
		"mov %B1,r0\n\t"  
		: "=m" (SPM_REG),
		  "=r" (retval)
		: "r" ((unsigned char)param),
		  "r" ((unsigned short)adr)
		: "r30", "r31", "r0"
	);
	return retval;
}