stm32使用ringbuffer实现串口通信

应用背景代码可以实现STM32战舰板子上的串口通信，因为只是实验用，所以主程序里是板子上两个串口互相通信，实际应用可以修改。关键技术环形缓冲，环形队列，使用指针，当指针指向缓冲区尾部后自动调回头部，实现环形缓冲

新建文件夹
CORE
core_cm3.crf
core_cm3.d
core_cm3.o
loopusart.axf
loopusart.c
loopusart.crf
loopusart.d
loopusart.h
loopusart.hex
loopusart.htm
loopusart.lnp
loopusart.map
loopusart.o
loopusart.plg
loopusart.sct
loopusart.tra
loopusart.uvgui.Administrator
loopusart.uvgui_Administrator.bak
loopusart.uvopt
loopusart.uvproj
loopusart_Target 1.dep
loopusart_uvopt.bak
loopusart_uvproj.bak
misc.crf
misc.d
misc.o
startup_stm32f10x_hd.d
startup_stm32f10x_hd.lst
startup_stm32f10x_hd.o
startup_stm32f10x_hd.s
stm32f10x_adc.crf
stm32f10x_adc.d
stm32f10x_adc.__i
stm32f10x_bkp.crf
stm32f10x_bkp.d
stm32f10x_bkp.__i
stm32f10x_can.crf
stm32f10x_can.d
stm32f10x_can.__i
stm32f10x_cec.crf
stm32f10x_cec.d
stm32f10x_cec.__i
stm32f10x_crc.crf
stm32f10x_crc.d
stm32f10x_crc.__i
stm32f10x_dac.crf
stm32f10x_dac.d
stm32f10x_dac.__i
stm32f10x_dbgmcu.crf
stm32f10x_dbgmcu.d
stm32f10x_dbgmcu.__i
stm32f10x_dma.crf
stm32f10x_dma.d
stm32f10x_dma.__i
stm32f10x_exti.crf
stm32f10x_exti.d
stm32f10x_exti.__i
stm32f10x_flash.crf
stm32f10x_flash.d
stm32f10x_flash.__i
stm32f10x_fsmc.crf
stm32f10x_fsmc.d
stm32f10x_fsmc.__i
STM32F10x_FWLib
stm32f10x_gpio.crf
stm32f10x_gpio.d
stm32f10x_gpio.o
stm32f10x_i2c.crf
stm32f10x_i2c.d
stm32f10x_i2c.__i
stm32f10x_iwdg.crf
stm32f10x_iwdg.d
stm32f10x_iwdg.__i
stm32f10x_pwr.crf
stm32f10x_pwr.d
stm32f10x_pwr.__i
stm32f10x_rcc.crf
stm32f10x_rcc.d
stm32f10x_rcc.o
stm32f10x_rtc.crf
stm32f10x_rtc.d
stm32f10x_rtc.__i
stm32f10x_sdio.crf
stm32f10x_sdio.d
stm32f10x_sdio.__i
stm32f10x_spi.crf
stm32f10x_spi.d
stm32f10x_spi.__i
stm32f10x_tim.crf
stm32f10x_tim.d
stm32f10x_tim.__i
stm32f10x_usart.crf
stm32f10x_usart.d
stm32f10x_usart.o
stm32f10x_wwdg.crf
stm32f10x_wwdg.d
stm32f10x_wwdg.__i
sys.c
sys.crf
sys.d
sys.h
sys.__i
test.c
test.crf
test.d
test.o
test.__i