我进行了搜索，但没有一个答案真正解释了我所看到的。
我有一个正确编译的文件，并添加了一个新的包含：
#include "libopencm3/stm32/usart.h"
再次编译就好了。现在，我添加一个函数：
void usart_setup(void)
{
/* Setup USART6 parameters. */
usart_set_baudrate(USART6, 38400);
usart_set_databits(USART6, 8);
usart_set_stopbits(USART6, USART_STOPBITS_1);
usart_set_mode(USART6, USART_MODE_TX);
usart_set_parity(USART6, USART_PARITY_NONE);
usart_set_flow_control(USART6, USART_FLOWCONTROL_NONE);
/* Finally enable the USART. */
usart_enable(USART6);
}
现在我得到：
/home/troy/projects/131114troy/tests/gpio1/trunk/gpio.c:137: undefined reference to `usart_set_baudrate'
/home/troy/projects/131114troy/tests/gpio1/trunk/gpio.c:138: undefined reference to `usart_set_databits'
/home/troy/projects/131114troy/tests/gpio1/trunk/gpio.c:139: undefined reference to `usart_set_stopbits'
/home/troy/projects/131114troy/tests/gpio1/trunk/gpio.c:140: undefined reference to `usart_set_mode'
/home/troy/projects/131114troy/tests/gpio1/trunk/gpio.c:141: undefined reference to `usart_set_parity'
/home/troy/projects/131114troy/tests/gpio1/trunk/gpio.c:142: undefined reference to `usart_set_flow_control'
/home/troy/projects/131114troy/tests/gpio1/trunk/gpio.c:145: undefined reference to `usart_enable'
这是 usart.h 文件：
/*
* This file is part of the libopencm3 project.
*
* Copyright (C) 2009 Uwe Hermann <uwe@hermann-uwe.de>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef LIBOPENCM3_USART_H
#define LIBOPENCM3_USART_H
#include <libopencm3/stm32/memorymap.h>
#include <libopencm3/cm3/common.h>
/* --- Convenience macros -------------------------------------------------- */
#define USART1 USART1_BASE
#define USART2 USART2_BASE
#define USART3 USART3_BASE
#define UART4 UART4_BASE
#define UART5 UART5_BASE
#define USART6 USART6_BASE
/* --- USART registers ----------------------------------------------------- */
/* Status register (USARTx_SR) */
#define USART_SR(usart_base) MMIO32(usart_base + 0x00)
#define USART1_SR USART_SR(USART1_BASE)
#define USART2_SR USART_SR(USART2_BASE)
#define USART3_SR USART_SR(USART3_BASE)
#define UART4_SR USART_SR(UART4_BASE)
#define UART5_SR USART_SR(UART5_BASE)
#define USART6_SR USART_SR(USART6_BASE)
/* Data register (USARTx_DR) */
#define USART_DR(usart_base) MMIO32(usart_base + 0x04)
#define USART1_DR USART_DR(USART1_BASE)
#define USART2_DR USART_DR(USART2_BASE)
#define USART3_DR USART_DR(USART3_BASE)
#define UART4_DR USART_DR(UART4_BASE)
#define UART5_DR USART_DR(UART5_BASE)
#define USART6_DR USART_DR(USART6_BASE)
/* Baud rate register (USARTx_BRR) */
#define USART_BRR(usart_base) MMIO32(usart_base + 0x08)
#define USART1_BRR USART_BRR(USART1_BASE)
#define USART2_BRR USART_BRR(USART2_BASE)
#define USART3_BRR USART_BRR(USART3_BASE)
#define UART4_BRR USART_BRR(UART4_BASE)
#define UART5_BRR USART_BRR(UART5_BASE)
#define USART6_BRR USART_BRR(USART6_BASE)
/* Control register 1 (USARTx_CR1) */
#define USART_CR1(usart_base) MMIO32(usart_base + 0x0c)
#define USART1_CR1 USART_CR1(USART1_BASE)
#define USART2_CR1 USART_CR1(USART2_BASE)
#define USART3_CR1 USART_CR1(USART3_BASE)
#define UART4_CR1 USART_CR1(UART4_BASE)
#define UART5_CR1 USART_CR1(UART5_BASE)
#define USART6_CR1 USART_CR1(USART6_BASE)
/* Control register 2 (USARTx_CR2) */
#define USART_CR2(usart_base) MMIO32(usart_base + 0x10)
#define USART1_CR2 USART_CR2(USART1_BASE)
#define USART2_CR2 USART_CR2(USART2_BASE)
#define USART3_CR2 USART_CR2(USART3_BASE)
#define UART4_CR2 USART_CR2(UART4_BASE)
#define UART5_CR2 USART_CR2(UART5_BASE)
#define USART6_CR2 USART_CR2(USART6_BASE)
/* Control register 3 (USARTx_CR3) */
#define USART_CR3(usart_base) MMIO32(usart_base + 0x14)
#define USART1_CR3 USART_CR3(USART1_BASE)
#define USART2_CR3 USART_CR3(USART2_BASE)
#define USART3_CR3 USART_CR3(USART3_BASE)
#define UART4_CR3 USART_CR3(UART4_BASE)
#define UART5_CR3 USART_CR3(UART5_BASE)
#define USART6_CR3 USART_CR3(USART6_BASE)
/* Guard time and prescaler register (USARTx_GTPR) */
#define USART_GTPR(usart_base) MMIO32(usart_base + 0x18)
#define USART1_GTPR USART_GTPR(USART1_BASE)
#define USART2_GTPR USART_GTPR(USART2_BASE)
#define USART3_GTPR USART_GTPR(USART3_BASE)
#define UART4_GTPR USART_GTPR(UART4_BASE)
#define UART5_GTPR USART_GTPR(UART5_BASE)
#define USART6_GTPR USART_GTPR(USART6_BASE)
/* --- USART_SR values ----------------------------------------------------- */
/* CTS: CTS flag */
/* Note: N/A on UART4/5 */
#define USART_SR_CTS (1 << 9)
/* LBD: LIN break detection flag */
#define USART_SR_LBD (1 << 8)
/* TXE: Transmit data buffer empty */
#define USART_SR_TXE (1 << 7)
/* TC: Transmission complete */
#define USART_SR_TC (1 << 6)
/* RXNE: Read data register not empty */
#define USART_SR_RXNE (1 << 5)
/* IDLE: Idle line detected */
#define USART_SR_IDLE (1 << 4)
/* ORE: Overrun error */
#define USART_SR_ORE (1 << 3)
/* NE: Noise error flag */
#define USART_SR_NE (1 << 2)
/* FE: Framing error */
#define USART_SR_FE (1 << 1)
/* PE: Parity error */
#define USART_SR_PE (1 << 0)
/* --- USART_DR values ----------------------------------------------------- */
/* USART_DR[8:0]: DR[8:0]: Data value */
#define USART_DR_MASK 0x1FF
/* --- USART_BRR values ---------------------------------------------------- */
/* DIV_Mantissa[11:0]: mantissa of USARTDIV */
#define USART_BRR_DIV_MANTISSA_MASK (0xFFF << 4)
/* DIV_Fraction[3:0]: fraction of USARTDIV */
#define USART_BRR_DIV_FRACTION_MASK 0xF
/* --- USART_CR1 values ---------------------------------------------------- */
/* UE: USART enable */
#define USART_CR1_UE (1 << 13)
/* M: Word length */
#define USART_CR1_M (1 << 12)
/* WAKE: Wakeup method */
#define USART_CR1_WAKE (1 << 11)
/* PCE: Parity control enable */
#define USART_CR1_PCE (1 << 10)
/* PS: Parity selection */
#define USART_CR1_PS (1 << 9)
/* PEIE: PE interrupt enable */
#define USART_CR1_PEIE (1 << 8)
/* TXEIE: TXE interrupt enable */
#define USART_CR1_TXEIE (1 << 7)
/* TCIE: Transmission complete interrupt enable */
#define USART_CR1_TCIE (1 << 6)
/* RXNEIE: RXNE interrupt enable */
#define USART_CR1_RXNEIE (1 << 5)
/* IDLEIE: IDLE interrupt enable */
#define USART_CR1_IDLEIE (1 << 4)
/* TE: Transmitter enable */
#define USART_CR1_TE (1 << 3)
/* RE: Receiver enable */
#define USART_CR1_RE (1 << 2)
/* RWU: Receiver wakeup */
#define USART_CR1_RWU (1 << 1)
/* SBK: Send break */
#define USART_CR1_SBK (1 << 0)
/* --- USART_CR2 values ---------------------------------------------------- */
/* LINEN: LIN mode enable */
#define USART_CR2_LINEN (1 << 14)
/* STOP[13:12]: STOP bits */
#define USART_CR2_STOPBITS_1 (0x00 << 12) /* 1 stop bit */
#define USART_CR2_STOPBITS_0_5 (0x01 << 12) /* 0.5 stop bits */
#define USART_CR2_STOPBITS_2 (0x02 << 12) /* 2 stop bits */
#define USART_CR2_STOPBITS_1_5 (0x03 << 12) /* 1.5 stop bits */
#define USART_CR2_STOPBITS_MASK (0x03 << 12)
#define USART_CR2_STOPBITS_SHIFT 12
/* CLKEN: Clock enable */
#define USART_CR2_CLKEN (1 << 11)
/* CPOL: Clock polarity */
#define USART_CR2_CPOL (1 << 10)
/* CPHA: Clock phase */
#define USART_CR2_CPHA (1 << 9)
/* LBCL: Last bit clock pulse */
#define USART_CR2_LBCL (1 << 8)
/* LBDIE: LIN break detection interrupt enable */
#define USART_CR2_LBDIE (1 << 6)
/* LBDL: LIN break detection length */
#define USART_CR2_LBDL (1 << 5)
/* ADD[3:0]: Addres of the usart node */
#define USART_CR2_ADD_MASK 0xF
/* --- USART_CR3 values ---------------------------------------------------- */
/* CTSIE: CTS interrupt enable */
/* Note: N/A on UART4 & UART5 */
#define USART_CR3_CTSIE (1 << 10)
/* CTSE: CTS enable */
/* Note: N/A on UART4 & UART5 */
#define USART_CR3_CTSE (1 << 9)
/* RTSE: RTS enable */
/* Note: N/A on UART4 & UART5 */
#define USART_CR3_RTSE (1 << 8)
/* DMAT: DMA enable transmitter */
/* Note: N/A on UART5 */
#define USART_CR3_DMAT (1 << 7)
/* DMAR: DMA enable receiver */
/* Note: N/A on UART5 */
#define USART_CR3_DMAR (1 << 6)
/* SCEN: Smartcard mode enable */
/* Note: N/A on UART4 & UART5 */
#define USART_CR3_SCEN (1 << 5)
/* NACK: Smartcard NACK enable */
/* Note: N/A on UART4 & UART5 */
#define USART_CR3_NACK (1 << 4)
/* HDSEL: Half-duplex selection */
#define USART_CR3_HDSEL (1 << 3)
/* IRLP: IrDA low-power */
#define USART_CR3_IRLP (1 << 2)
/* IREN: IrDA mode enable */
#define USART_CR3_IREN (1 << 1)
/* EIE: Error interrupt enable */
#define USART_CR3_EIE (1 << 0)
/* --- USART_GTPR values --------------------------------------------------- */
/* GT[7:0]: Guard time value */
/* Note: N/A on UART4 & UART5 */
#define USART_GTPR_GT_MASK (0xFF << 8)
/* PSC[7:0]: Prescaler value */
/* Note: N/A on UART4/5 */
#define USART_GTPR_PSC_MASK 0xFF
/* TODO */ /* Note to Uwe: what needs to be done here? */
/* --- Convenience defines ------------------------------------------------- */
/* CR1_PCE / CR1_PS combined values */
#define USART_PARITY_NONE 0x00
#define USART_PARITY_ODD USART_CR1_PS
#define USART_PARITY_EVEN (USART_CR1_PS | USART_CR1_PCE)
#define USART_PARITY_MASK (USART_CR1_PS | USART_CR1_PCE)
/* CR1_TE/CR1_RE combined values */
#define USART_MODE_RX USART_CR1_RE
#define USART_MODE_TX USART_CR1_TE
#define USART_MODE_TX_RX (USART_CR1_RE | USART_CR1_TE)
#define USART_MODE_MASK (USART_CR1_RE | USART_CR1_TE)
#define USART_STOPBITS_1 USART_CR2_STOPBITS_1 /* 1 stop bit */
#define USART_STOPBITS_0_5 USART_CR2_STOPBITS_0_5 /* 0.5 stop bits */
#define USART_STOPBITS_2 USART_CR2_STOPBITS_2 /* 2 stop bits */
#define USART_STOPBITS_1_5 USART_CR2_STOPBITS_1_5 /* 1.5 stop bits */
/* CR3_CTSE/CR3_RTSE combined values */
#define USART_FLOWCONTROL_NONE 0x00
#define USART_FLOWCONTROL_RTS USART_CR3_RTSE
#define USART_FLOWCONTROL_CTS USART_CR3_CTSE
#define USART_FLOWCONTROL_RTS_CTS (USART_CR3_RTSE | USART_CR3_CTSE)
#define USART_FLOWCONTROL_MASK (USART_CR3_RTSE | USART_CR3_CTSE)
/* --- Function prototypes ------------------------------------------------- */
void usart_set_baudrate(u32 usart, u32 baud);
void usart_set_databits(u32 usart, u32 bits);
void usart_set_stopbits(u32 usart, u32 stopbits);
void usart_set_parity(u32 usart, u32 parity);
void usart_set_mode(u32 usart, u32 mode);
void usart_set_flow_control(u32 usart, u32 flowcontrol);
void usart_enable(u32 usart);
void usart_disable(u32 usart);
void usart_send(u32 usart, u16 data);
u16 usart_recv(u32 usart);
void usart_wait_send_ready(u32 usart);
void usart_wait_recv_ready(u32 usart);
void usart_send_blocking(u32 usart, u16 data);
u16 usart_recv_blocking(u32 usart);
void usart_enable_rx_dma(u32 usart);
void usart_disable_rx_dma(u32 usart);
void usart_enable_tx_dma(u32 usart);
void usart_disable_tx_dma(u32 usart);
#endif
如果我注释掉该行void usart_set_baudrate(u32 usart, u32 baud);，我会收到额外的警告：
gpio.c:137:5: warning: implicit declaration of function 'usart_set_baudrate'
所以它似乎至少在某种程度上正在发挥作用。C++ 有点新，所以不太确定我还能尝试什么。任何指针？
生成文件：
# Name of the .c file with 'main' as well as output file name
NAME = gpio
# Linker file
LDFILE =stm32_flash.ld
# Current directory
CURDIR=.
SRCS = $(NAME).c startup_stm32f4xx.s syscalls.c
###################################################
# Check for valid float argument
# NOTE that you have to run make clean after
# changing these as hardfloat and softfloat are not
# binary compatible
ifneq ($(FLOAT_TYPE), hard)
ifneq ($(FLOAT_TYPE), soft)
override FLOAT_TYPE = soft
endif
endif
###################################################
# Prefix the name for the particular toolchain
PREFIX = arm-none-eabi-
TOOLDIR =~/CodeSourcery/Sourcery_G++_Lite/bin
CC =$(TOOLDIR)/$(PREFIX)gcc
LD =$(TOOLDIR)/$(PREFIX)ld
OBJCOPY =$(TOOLDIR)/$(PREFIX)objcopy
SIZE =$(TOOLDIR)/$(PREFIX)size
OBJDUMP =$(TOOLDIR)/$(PREFIX)objdump
CFLAGS = -std=gnu99 -g -Os -Wall
CFLAGS += -mlittle-endian -mthumb -mthumb-interwork -nostartfiles -mcpu=cortex-m4
ifeq ($(FLOAT_TYPE), hard)
CFLAGS += -fsingle-precision-constant -Wdouble-promotion
CFLAGS += -mfpu=fpv4-sp-d16 -mfloat-abi=hard
else
CFLAGS += -msoft-float
endif
###################################################
# Directory path--includes for .h and .c files common to all routines
LIBCOMMONALL = $(CURDIR)/../../../common_all/trunk
# Navigation to libraries specific to the f4 and discoveryf4
LIBF4D = $(CURDIR)/../../../sw_discoveryf4/trunk
# Routes to USB
LIBUSB = $(LIBF4D)/STM32F4_USB_CDC
# Includes--ST USB
CFLAGS += -I$(LIBUSB)/inc
CFLAGS += -I$(LIBUSB)/inc/StdPeriph/inc
CFLAGS += -I$(LIBUSB)/lib/StdPeriph/inc
CFLAGS += -I$(LIBUSB)/lib/USB_OTG/inc
CFLAGS += -I$(LIBUSB)/inc/USB_Device/Core/inc
CFLAGS += -I$(LIBUSB)/inc/USB_Device/Class/cdc/inc
CFLAGS += -I$(LIBUSB)/lib/Core/stm32
CFLAGS += -I$(LIBUSB)/lib/Core/cmsis
CFLAGS += -I$(LIBUSB)/lib/USB_Device/Class/cdc/inc
CFLAGS += -I$(LIBUSB)/lib/USB_Device/Core/inc/
# Includes--our stuff
CFLAGS += -I$(LIBCOMMONALL)
CFLAGS += -I$(LIBF4D)/lib/libdiscoveryf4
CFLAGS += -I$(LIBF4D)/lib/libmiscstm32f4
CFLAGS += -I$(LIBF4D)/lib/libusartstm32f4
CFLAGS += -I$(LIBF4D)/lib
# Library paths--ST USB
LIBPATHS = -L$(LIBUSB)
LIBPATHS += -L$(LIBUSB)/lib/StdPeriph
LIBPATHS += -L$(LIBUSB)/lib/USB_Device/Core
LIBPATHS += -L$(LIBUSB)/lib/USB_Device/Class/cdc
LIBPATHS += -L$(LIBUSB)/lib/USB_OTG
# Library paths--our stuff
LIBPATHS += -L$(LIBF4D)/lib/libdiscoveryf4
LIBPATHS += -L$(LIBF4D)/lib/libmiscstm32f4
LIBPATHS += -L$(LIBCOMMONALL)/stm32
# Libraries to link
# USB
LIBS = -lm -lusbf4 -lstdperiph -lusbdevcdc -lusbcore -lusbdevcore -lusbf4 -lstdperiph
# our stuff
LIBS += -ldiscoveryf4 -lmiscstm32f4
LDFLAGS = -T$(LDFILE)
OBJS = $(SRCS:.c=.o)
###################################################
.PHONY: proj
all: proj
$(SIZE) $(NAME).elf
proj: $(NAME).elf
$(NAME).elf: $(SRCS)
$(CC) $(CFLAGS) $^ -o $@ $(LIBPATHS) $(LIBS) $(LDFLAGS)
$(OBJCOPY) -O ihex $(NAME).elf $(NAME).hex
$(OBJCOPY) -O binary $(NAME).elf $(NAME).bin
$(OBJDUMP) -S $(NAME).elf > $(NAME).list
clean:
rm -f *.o
rm -f $(NAME).elf
rm -f $(NAME).hex
rm -f $(NAME).bin
# $(MAKE) clean -C lib # Remove this line if you don't want to clean the libs as well
flash: images
@printf " FLASHING $(NAME)\n"
@# IMPORTANT: Don't use "resume", only "reset" will work correctly!
# Kill running instances of the server
# killall st-util
st-flash write $(NAME).bin 0x08000000
.PHONY: images clean