RE: [avr-gcc-list] eicall on ATmega2561

[Stu Bell]

This is not a complete answer to your problem, but it's mostly there.

 

Following is the code I use to call my DownloadFirmware entry point in the bootloader:

 

  /*  We don't care about a result because we'll be reloaded and never
   *  come back to this point.
   *
   *  We have to assemble this instruction because we're using an ATmega2560,
   *  and have to address the high memory in flash.  That means the address
   *  of AppDownloadFirmware MUST be 0x1F400 (0x3E800, byte addressed).
   */
//  AppDownloadFirmware();
    asm volatile ( "ldi  r24, 0x01   \n\t"
                   "out  0x3C, r24   \n\t"
                   "ldi  r30, 0x00   \n\t"
                   "ldi  r31, 0xf4   \n\t"
                   ".word 0x9519 ;eicall \n\t"
                 );

The reason I say this is "incomplete" is that I know the call to AppDownloadFirmware() in the bootloader will not return.  Instead, the firmware will be overwritten and the CPU reset.  That means I don't care about clobbered registers.  Also, the jump location is hardwired.

 

You can take this to the next step by making this an inline function, passing in the function address, and protecting the registers you clobber so the processor can return (if you want).

 

Also, when I wrote this, the inline assembler did not grok the EICALL instruction so I had to hand-assemble it.  You may be able to just use the instruction now.

 

I hope this helps!

 

Best regards,

Stu Bell
DataPlay (DPHI, Inc.)

 

---

From: address@hidden [mailto:address@hidden On Behalf Of Dusan Ferbas
Sent: Monday, August 04, 2008 8:37 AM
To: address@hidden
Subject: [avr-gcc-list] eicall on ATmega2561

Hi,

we are trying to call a bootloader function from 
application. According to data, different function is used there (eeprom, flash, 
SPI flash).
We have a problem, because it does not work. I consulted with 
Andy Hutchinson a while ago, we investigated little more, but something more is 
needed :-).
In other words it looks like EIND seeding does not 
work.

Are we missing to setup something ?

Is there a way, how to 
say to a GCC compiler, that asm part modifies specific regs ?
For AVR, they 
are used to pass arguments.
Or is it a better way to create an inline 
function ?

...
it did not work leaving all work to compiler 
(WinAVR-20080610 used)
-----------------------------------------
  
unsigned char eind_local = EIND;
  EIND = 0x3F800 >> (16 + 1); 
//highest LoadAddr bits  (for Atmega2561 == 1, because it is a word 
address)
  BootInfoHeader->fn[id](address, p_data, size);
  
EIND = eind_local;

to be sure, what is happening (EIND seeding and 
restore left in C)
---------------------------------------
unsigned short 
call_address = (unsigned short)BootInfoHeader->fn[id];
asm volatile 
(
    "movw r30,%3" "\n\t"   //indirect 
call
    "push r20" "\n\t"      
//preserve regs, used for args
    "push r21" 
"\n\t"
    "push r22" "\n\t"
    "push r23" 
"\n\t"
    "movw r20,%0" "\n\t"   //load 
args
    "movw r22,%1" "\n\t"
    "movw 
r24,%2" "\n\t" 
    "eicall" "\n\t"
    "pop 
r23" "\n\t"       //restore 
regs
    "pop r22" "\n\t"
    "pop r21" 
"\n\t"
    "pop r20"
    
::
    "r" (size),
    "r" 
(p_data),
    "r" (address),
    "r" 
(call_address)
    );

the only way, how it works (push 
return address, push call address and make a "ret" to it, EIND is not 
needed)
-------------------------------------
unsigned char low_address = 
call_address & 0xFF;
unsigned char high_address = (call_address >> 
8 ) & 0xFF;

unsigned char low_pc = 
0x38;

    

        

//computed from .lst and 
.map
unsigned char high_pc = 0xFA;

asm volatile (
  "push r20" 
"\n\t"
  "push r21" "\n\t"
  "push r22" "\n\t"
  "push 
r23" "\n\t"
  "push %5" "\n\t"
  "push %6" "\n\t"
  "ldi 
r20,lo8(1)" "\n\t"
  "push r20" "\n\t"
  "push %3" 
"\n\t"
  "push %4" "\n\t"
  "push r20" "\n\t"
  "movw 
r20,%0" "\n\t"
  "movw r22,%1" "\n\t"
  "movw r24,%2" "\n\t" 
  "ret" "\n\t"
  "pop r23" "\n\t" 
  "pop r22" 
"\n\t"
  "pop r21" "\n\t"
  "pop r20"
  ::
  "r" 
(size),
  "r" (p_data),
  "r" (address),
  "r" 
(low_address),
  "r" (high_address),
  "r" (low_pc),
  
"r" (high_pc)
  );

Dusan Ferbas
www.etech.cz