Gcc/10.2.0/gcc/AVR-Built 002din-Functions
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6.60.10 AVR Built-in Functions
For each built-in function for AVR, there is an equally named,
uppercase built-in macro defined. That way users can easily query if
or if not a specific built-in is implemented or not. For example, if
__builtin_avr_nop
is available the macro
__BUILTIN_AVR_NOP
is defined to 1
and undefined otherwise.
void __builtin_avr_nop (void)
void __builtin_avr_sei (void)
void __builtin_avr_cli (void)
void __builtin_avr_sleep (void)
void __builtin_avr_wdr (void)
unsigned char __builtin_avr_swap (unsigned char)
unsigned int __builtin_avr_fmul (unsigned char, unsigned char)
int __builtin_avr_fmuls (char, char)
int __builtin_avr_fmulsu (char, unsigned char)
These built-in functions map to the respective machine instruction, i.e.
nop
,sei
,cli
,sleep
,wdr
,swap
,fmul
,fmuls
resp.fmulsu
. The threefmul*
built-ins are implemented as library call if no hardware multiplier is available.void __builtin_avr_delay_cycles (unsigned long ticks)
Delay execution for
ticks
cycles. Note that this built-in does not take into account the effect of interrupts that might increase delay time.ticks
must be a compile-time integer constant; delays with a variable number of cycles are not supported.char __builtin_avr_flash_segment (const __memx void*)
This built-in takes a byte address to the 24-bit address space
__memx
and returns the number of the flash segment (the 64 KiB chunk) where the address points to. Counting starts at0
. If the address does not point to flash memory, return-1
.uint8_t __builtin_avr_insert_bits (uint32_t map, uint8_t bits, uint8_t val)
Insert bits from
bits
intoval
and return the resulting value. The nibbles ofmap
determine how the insertion is performed: LetX
be then
-th nibble ofmap
- If
X
is0xf
, then then
-th bit ofval
is returned unaltered. - If X is in the range 0…7,
then the
n
-th result bit is set to theX
-th bit ofbits
- If X is in the range 8…
0xe
, then then
-th result bit is undefined.
One typical use case for this built-in is adjusting input and output values to non-contiguous port layouts. Some examples:
// same as val, bits is unused __builtin_avr_insert_bits (0xffffffff, bits, val)
// same as bits, val is unused __builtin_avr_insert_bits (0x76543210, bits, val)
// same as rotating bits by 4 __builtin_avr_insert_bits (0x32107654, bits, 0)
// high nibble of result is the high nibble of val // low nibble of result is the low nibble of bits __builtin_avr_insert_bits (0xffff3210, bits, val)
// reverse the bit order of bits __builtin_avr_insert_bits (0x01234567, bits, 0)
- If
void __builtin_avr_nops (unsigned count)
Insert
count
NOP
instructions. The number of instructions must be a compile-time integer constant.
There are many more AVR-specific built-in functions that are used to
implement the ISO/IEC TR 18037 “Embedded C” fixed-point functions of
section 7.18a.6. You don’t need to use these built-ins directly.
Instead, use the declarations as supplied by the stdfix.h
header
with GNU-C99:
#include <stdfix.h> // Re-interpret the bit representation of unsigned 16-bit // integer uval as Q-format 0.16 value. unsigned fract get_bits (uint_ur_t uval) { return urbits (uval); }
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