URL:
<http://savannah.nongnu.org/bugs/?34423>
Summary: util/crc16.h: with -Os option inline functions are
called causing registers value loss
Project: AVR C Runtime Library
Submitted by: karol_grzybowski
Submitted on: Wed 28 Sep 2011 08:33:29 PM GMT
Category: Header
Severity: 3 - Normal
Priority: 5 - Normal
Item Group: libc code
Status: None
Percent Complete: 0%
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Release: 1.7.1
Fixed Release: None
_______________________________________________________
Details:
gcc 4.5.1, AVR_8_bit_GNU_Toolchain_3.2.3_315
gcc options: -funsigned-char -funsigned-bitfields -Os -fpack-struct
-fshort-enums -Wall -c -std=gnu99 -mmcu=atmega16
function:
static __inline__ uint8_t
_crc_ibutton_update(uint8_t __crc, uint8_t __data)
{
uint8_t __i, __pattern;
__asm__ __volatile__ (
" eor %0, %4" "\n\t"
" ldi %1, 8" "\n\t"
" ldi %2, 0x8C" "\n\t"
"1: lsr %0" "\n\t"
" brcc 2f" "\n\t"
" eor %0, %2" "\n\t"
"2: dec %1" "\n\t"
" brne 1b" "\n\t"
: "=r" (__crc), "=d" (__i), "=d" (__pattern)
: "0" (__crc), "r" (__data));
return __crc;
}
should be always inlined. In my code reading DS18B20 temperature:
// LSB of temp
data = ds_read_byte();
temp = (int16_t)data;
crc = _crc_ibutton_update(0, data);
// MSB of temp
data = ds_read_byte();
temp |= (int16_t)(data) << 8;
crc = _crc_ibutton_update(crc, data);
doesn't and that's why the MSB of temp is lost:
0e 94 44 00 call 0x88 ; 0x88 <_crc_ibutton_update>
Adding fallowing line to header seems to be the simplest solution of this
issue:
static __inline__ uint8_t _crc_ibutton_update(uint8_t __crc, uint8_t __data)
__attribute__((always_inline));
Probably the same problem may occur with others inline Assembly.
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