How to jump into bootloader in Ada? - embedded

Question

I am writing embedded code in Ada. I want to jump into bootloader code which is located at address 0x0E00. I am trying to use following code:
with Interfaces; use Interfaces;
with System;
package AVR.bootloader is
procedure Call;
pragma No_Return(Call);
pragma Import (Assembler,Call);
for Call'Address use System'To_Address (16#0E00#);
end AVR.bootloader;
The problem is this does not work.
Edit: I want to do a following C equivalent:
void (*boot)(void)=0x0E00;

Answer 1

I did a small experiment on this Macbook Pro, and your code seems to do what you meant it to; I modified the code to read
with System;
procedure Bootloader is
procedure Call;
pragma No_Return (Call);
pragma Import (Assembler, Call);
for Call'Address use System'To_Address (16#0E00#);
begin
Call;
end Bootloader;
and when I compile with gnatmake -c -u -f -S bootloader.adb the saved assembler is
.text
.globl __ada_bootloader
__ada_bootloader:
LFB1:
pushq %rbp
LCFI0:
movq %rsp, %rbp
LCFI1:
subq $16, %rsp
LCFI2:
movq $3584, -8(%rbp)
movq -8(%rbp), %rax
call *%rax
leave
LCFI3:
ret
[...]
which looks hopeful, though I’m not familiar enough with asm to know.
Running it under gdb I get (after a lot of chatter)
(gdb) run
Starting program: /Users/simon/tmp/bootloader
Reading symbols for shared libraries ++........................ done
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000e00
0x0000000000000e00 in ?? ()
(gdb) bt
#0 0x0000000000000e00 in ?? ()
Cannot access memory at address 0xe00
#1 0x0000000100000d93 in main (argc=1, argv=140734799805048, envp=140734799805064) at /Users/simon/tmp/b~bootloader.adb:121
#2 0x0000000100000bf4 in start ()
which looks even more hopeful.
Perhaps your AVR compiler isn’t code-generating properly?

Answer 2

Since normally a boot-loader runs on reset, the simplest method is to force a processor reset. A boot-loader may reasonably assume that it is running on an uninitialised system in reset state and may perform initialisation that is not valid on an already initialised system, so forcing a reset is the safest method.
Your processor may have a reset instruction or a reset controller that can perform this directly. Failing that it may have a watchdog timer that can generate a reset. Start the watchdog timer with a suitably short time-out and let it run without servicing it.