我找到了一段工作正常但我无法理解的内嵌汇编代码(链接):
// busy wait
__asm__ __volatile__ (
"1: sbiw %0,1" "\n\t" // 2 cycles
"brne 1b" : "=w" (us) : "0" (us) // 2 cycles
);
我找到了一些类似这个的gas教程,但是我找不到解释。无论如何,该文件可以通过avr-gcc编译:
/Applications/Arduino.app/Contents/Resources/Java/hardware/tools/avr/bin/avr-gcc -c -g -Os -Wall -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L -MMD -DUSB_VID=null -DUSB_PID=null -DARDUINO=105 -I/Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/cores/arduino -I/Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/variants/standard /Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/cores/arduino/wiring.c -o /var/folders/64/fwfkm1k51zbd4_c5lwpsbljh0000gn/T/build5450310618632673119.tmp/wiring.c.o
那么GCC内联汇编中的“=w”是什么意思?