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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.
These built-in functions map to the respective machine
instruction, i.e. nop, sei, cli, sleep,
wdr, swap, fmul, fmuls
resp. fmulsu. The three fmul* built-ins are implemented
as library call if no hardware multiplier is available.
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.
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 at 0.
If the address does not point to flash memory, return -1.
Insert bits from bits into val and return the resulting value. The nibbles of map determine how the insertion is performed: Let X be the n-th nibble of map
0xf,
then the n-th bit of val is returned unaltered.
0xe,
then the n-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);
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);
}
Next: Blackfin Built-in Functions, Previous: ARM ARMv8-M Security Extensions, Up: Target Builtins [Contents][Index]