Re: Bug in simulavr 1.1.0 for devices with little RAM?

[Georg-Johann Lay]

Am 24.03.24 um 12:23 schrieb Georg-Johann Lay:
> I am using SimulAVR 1.1.0 to run the AVR-LibC test suite and am
> hitting the following problem where it seems that the simulator
> is behaving different than the hardware:
>
> Take the C test case eeprom-5.c:

...here is a simpler test case.  It stores 24 to R24 where R26
holds the 8-bit address.  As ATtiny2313 has no RAM addresses
beyond 0xdf, this should actually work, irrespective of the
content of R27:

void test0 (void)
{
  __asm goto ("clr  r24"       "\n\t"
              "ldi  XL,  24"   "\n\t"
              "ldi  XH,  0xaa" "\n\t" // Garbage, should not matter.
              // Store 24 to R24
              "st   X,   XL"    "\n\t"
              "cpse r24, XL"    "\n\t"
              "%~jmp %x0"
              ::: "24", "26" : fail);
  return;

 fail:
  __builtin_exit (__LINE__);
}

int main (void)
{
  test0 ();
  return 0;
}

Johann


> #include <stdlib.h>
> #include <avr/eeprom.h>
>
> #define ADDR ((void*) 10)
>
> void test0 (void)
> {
>    eeprom_write_word (ADDR, 0x1234);
>
>    //__asm ("clr r27");
>    if (eeprom_read_word (ADDR) != 0x1234)
>        exit (__LINE__);
> }
>
> int main (void)
> {
>    test0 ();
>    return 0;
> }
>
> This writes 0x1234 to EEPROM and then reads it back again.
> Compile with (the Compiler and LibC versions don't matter;
> you can use avr-gcc v5.4 or v14 makes no difference):
>
> $ avr-gcc -mmcu=attiny2313 -Os eeprom-5.c -o eeprom-5.elf
>
> $ simulavr -d attiny2313 -T __stop_program -f eeprom-5.elf -C 
> core_avr_dump.core -m 60000000000
>
> WARNING: file /home/john/xgnu/source/simulavr/libsim/rwmem.cpp: line 
> 235: Invalid write access to IO[0xaa18]=0x34, PC=0x7a
> WARNING: file /home/john/xgnu/source/simulavr/libsim/rwmem.cpp: line 
> 235: Invalid write access to IO[0xaa19]=0x12, PC=0x7a
> Run finished.  Terminated at 6822750 ns (simulated) and
> 27292 cpu cycles
>
> The test case fails because the returned value from eeprom_read_word
> does not equal 0x1234.
>
> The eeprom_read_word implementation only sets the low byte (R26) of
> the RAM address (which points to the register file).  The high address
> is not set because ATtiny2313's RAM ends before 0x100 (RAM extends from
> 0x60 to 0xe0).  As far as I understand, the hardware of such devices
> just ignores the high byte of addresses when it reads/writes RAM.
>
> The test case above works when there is a "clr r27" prior to the
> eeprom_read_word call, but the current AVR-LibC implementation of
> assumes there is no need to set the hi8 part of the RAM address.
>
> Is this a bug in SimulAVR ?
> Or AVR-LibC making wrong assumptions on how the hardware behaves?
>
>
> Johann