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RE: [avr-gcc-list] ATmega 2561 - compiler generates eicall

From: Stu Bell
Subject: RE: [avr-gcc-list] ATmega 2561 - compiler generates eicall
Date: Wed, 4 Jun 2008 08:24:40 -0600

By the addresses it appears that you are using an ATmega2560 or 2561.
You are trying to use function pointers for upper flash (beyond the 128
Kbyte/64 Kword boundary).

The current GCC compiler does not know how to do this.  Function
pointers are kept as 2 byte entities.  While static (non-pointer)
function calls are dealt with using a neat device called a "trampoline"
(essentially a table of eijmps that the local function can call),
function pointers do not use this device.

I have the same problem and have resolved it by assigning all of my
pointer targets *and callers* into a separate linker section that is
forced into the lower part of flash.  I have the following macro:

   #define COMMAND_HANDLER   __attribute__ ((section (".fptr_target")))

Which I append to each function target prototype, for example:

CmdError CmdInitTrack( CmdPacket* pCmdPkt ) COMMAND_HANDLER;

Then, I created a custom linker script from avr6.x to place this section
in low flash:

. . .
  /* Internal text space or external memory.  */
  .text :
. . . 
    KEEP (*(.init8))
    *(.init9)  /* Call main().  */
    KEEP (*(.init9))
    /* Interrupt Service Routine code needs to be in the lower 128K
program */
    /* Any code that is the target of a function pointer must also 
       reside in lower memory */
    /* An RTOS task should also be in low mmeory. */
    /* Main code starts here - this code can oveflow into the upper 128K
program */
    . = ALIGN(2);
    . = ALIGN(2);
    *(.fini9)  /* _exit() starts here.  */
. . . 

As you may notice, there are also two other custom sections, .isr and
.task.  All ISRs go into the .isr section for the same reason as the
function pointer targets -- the vector table will default jump only to
the low part of flash.  I accomplished this by having the following

    #define ISR_SECTION __attribute__ ((section (".isr")))

And making all of my ISR declarations...


(Note the lack of a comma between ISR_BLOCK and ISR_SECTION -- not sure
why that must be, but it did not compile if a comma was there.)

The .task section is for RTOS task functions.  Since the tasks are
created at run time by pssing a function pointer to the task creation
mechanism, they fall under the same rules as the function pointers.

Using these techniques I have been able to get my code running under
WinAVR 20080521.  Hopefully, you can to.

Best of luck!

Best regards, 

Stu Bell 
DataPlay (DPHI, Inc.) 

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of
Dusan Ferbas
Sent: Tuesday, June 03, 2008 5:36 PM
To: address@hidden
Subject: [avr-gcc-list] ATmega 2561 - compiler generates eicall


I am using WinAVR-20071221, because none of the most recent toolchains
produces a runnable code for our application.

Our bootloader starts at 0x3f800 (2kB).
In its code, we are using function[id](...) construction.
This is compiled with eicall instruction, but no EIND register is set.
Is there a way, how to tell the compiler, that code is linked in upper
half of flash ?
In bootloader code we can live with EIND=1 at its init.

But when we have a call from our application, neither EIND is set, even
address is not divided by 2 (WinAVR bug #1959227).
Probably some far attribute should be applied ?
When compiled for ATmega128 (with 0x1f806), it works ...

typedef void boot_loader_init(unsigned  char *);
#define boot_loader_data_init           ((boot_loader_init *)0x3F806)


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