关于C#：AVR ATmega在主循环之前使用printf时会不断重置

AVR ATmega keeps resetting while using printf before main loop

我正在AVR ATmega328P微控制器上使用avr-libc开发C应用程序。由于我没有ICE调试器，因此我按照这些说明和本教程进行操作，以使stdio.h功能(例如printf)能够将硬件UART用作stdout。

那行得通，我可以在连接到目标板上的PC终端上看到输出，但是奇怪的是：当我在主处理器上只有一个printf时，但是在主循环之前，有什么东西导致处理器复位，而如果我只有printf仅在主循环内或在主循环与循环内之前有效，则它运行良好。像这样：

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#include <stdio.h>

/* stream definitions for UART input/output */
FILE uart_output = FDEV_SETUP_STREAM(uart_drv_send_byte, NULL, _FDEV_SETUP_WRITE);
FILE uart_input = FDEV_SETUP_STREAM(NULL, uart_drv_read_byte, _FDEV_SETUP_READ);

int main() {
/* Definition of stdout and stdin */
stdout = &uart_output;
stdin = &uart_input;

/* Configures Timer1 for generating a compare interrupt each 1ms (1kHz) */
timer_init()

/* UART initialization */
uart_drv_start(UBRRH_VALUE, UBRRL_VALUE, USE_2X, &PORTB, 2);

/* Sets the sleep mode to idle */
set_sleep_mode(SLEEP_MODE_IDLE);

printf("START");

/* main loop */
while(1) {
printf("LOOP");

/* Sleeps so the main loop iterates only on interrupts (avoids busy loop) */
sleep_mode();
}
}

上面的代码产生以下输出：

1	START LOOP LOOP LOOP LOOP LOOP LOOP ... LOOP

这是预期的。如果我们注释printf("START")行，它将产生以下内容：

1	LOOP LOOP LOOP LOOP LOOP LOOP LOOP ... LOOP

也可以问题是，如果我在while循环内没有任何printf，它会像这样：

1	START START START START START START ... START

这清楚地表明处理器正在重新启动，因为预期的输出将只是一个START，而无限循环仅在1kHz定时器中断时才被唤醒。为什么会这样呢？我要强调的是，没有配置看门狗定时器(如果有，则仅打印LOOP的情况也会被新的START中断)。

使用GPIO引脚监控执行

为了了解情况，我围绕主循环中有问题的print("START")和sleep_mode打开和关闭了GPIO引脚：

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int main() {

/* Irrelevant parts suppressed... */

GPIO1_ON;
printf("START");
GPIO1_OFF;

/* Main loop */
while(1) {

/* Sleeps so the main loop iterates only on interrupts (avoids busy loop) */
GPIO2_ON;
sleep_mode();
GPIO2_OFF;
}
}

事实证明，GPIO1保持打开状态持续132μs(printf("START")调用时间)，然后保持关闭状态6.6ms(大约是以9600bit / s的速度传输六个字符的时间)，而GPIO2切换12次(两次中断的次数是6次：准备发送中断和UART空数据寄存器中断)，在GPIO1再次导通之前，睡眠又活动了1.4ms，这表明新的printf("START")-因此在复位之后。我可能必须检查一下UART代码，但是我很确定非中断UART版本也会出现相同的问题，并且这也不能解释为什么在主循环中使用printf可以正常工作，不会发生复位(我希望在任何情况下，如果UART代码出错，都会发生复位)。

(已解决！)：为完整起见，UART初始化和发送代码如下**

这是我为AVR编写一个中断驱动的UART驱动程序的第一次尝试，但是可以在RS-232或RS-485上使用，在发送数据时需要激活TX_ENABLE引脚。事实证明，由于我必须使代码在ATmega328P或ATmega644上都可以使用，因此中断向量具有不同的名称，因此我根据所使用的处理器使用了#define TX_VECTOR来假定正确的名称。在制作和测试驱动程序的过程中，为UDRE数据空中断选择" TX_VECTOR"最终掩盖了我尚未定义USART0_TX_vect的事实(此工作正在进行中，无论如何我可能都不需要两者) ...)

现在，我刚刚为USART0_TX_vect定义了一个空的中断服务例程(ISR)，并且此操作不再复位，显示@PeterGibson正确地设置了它。非常感谢！

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// Interrupt vectors for Atmega328P
#if defined(__AVR_ATmega328P__)
#define RX_VECTOR USART_RX_vect
#define TX_VECTOR USART_UDRE_vect
// Interrupt vectors for Atmega644
#elif defined(__AVR_ATmega644P__)
#define RX_VECTOR USART0_RX_vect
#define TX_VECTOR USART0_UDRE_vect
#endif

ISR(TX_VECTOR)
{
uint8_t byte;

if (!ringbuffer_read_byte(&txrb, &byte)) {

/* If RS-485 is enabled, sets TX_ENABLE high */
if (TX_ENABLE_PORT)
*TX_ENABLE_PORT |= _BV(TX_ENABLE_PIN);
UDR0 = byte;
}
else {
/* No more chars to be read from ringbuffer, disables empty
* data register interrupt */
UCSR0B &= ~_BV(UDRIE0);
}

/* If RS-485 mode is on and the interrupt was called with TXC0 set it
* means transmission is over. TX_ENABLED should be cleared. */
if ((TX_ENABLE_PORT) && (UCSR0A & _BV(TXC0) & _BV(UDR0))) {
*TX_ENABLE_PORT &= ~_BV(TX_ENABLE_PIN);
UCSR0B &= ~_BV(UDRIE0);
}
}

void uart_drv_start(uint8_t ubrrh, uint8_t ubrrl, uint8_t use2x,
volatile uint8_t* rs485_tx_enable_io_port,
uint8_t rs485_tx_enable_io_pin)
{
/* Initializes TX and RX ring buffers */
ringbuffer_init(&txrb, &tx_buffer[0], UART_TX_BUFSIZE);
ringbuffer_init(&rxrb, &rx_buffer[0], UART_RX_BUFSIZE);

/* Disables UART */
UCSR0B = 0x00;

/* Initializes baud rate */
UBRR0H = ubrrh;
UBRR0L = ubrrl;
if (use2x)
UCSR0A |= _BV(U2X0);
else
UCSR0A &= ~_BV(U2X0);

/* Configures async 8N1 operation */
UCSR0C = _BV(UCSZ00) | _BV(UCSZ01);

/* If a port was specified for a pin to be used as a RS-485 driver TX_ENABLE,
* configures the pin as output and enables the TX data register empty
* interrupt so it gets disabled in the end of transmission */
if (rs485_tx_enable_io_port) {
TX_ENABLE_PORT = rs485_tx_enable_io_port;
TX_ENABLE_PIN = rs485_tx_enable_io_pin;
/* Configures the RS-485 driver as an output (on the datasheet the data
* direction register is always on the byte preceding the I/O port addr) */
*(TX_ENABLE_PORT-1) |= _BV(TX_ENABLE_PIN);
/* Clears TX_ENABLE pin (active high) */
*TX_ENABLE_PORT &= ~_BV(TX_ENABLE_PIN);
/* Enables end of transmission interrupt */
UCSR0B = _BV(TXCIE0);
}
/* Enables receptor, transmitter and RX complete interrupts */
UCSR0B |= _BV(RXEN0) | _BV(TXEN0) | _BV(RXCIE0);
}

固定的UART代码(现在工作100％！)

为了帮助对AVR ATmega感兴趣或开发类似的中断驱动UART驱动程序的任何人，此处提供了上面已解决和测试的问题的代码。感谢所有帮助我发现缺少ISR的问题的人！

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// Interrupt vectors for Atmega328P
#if defined(__AVR_ATmega328P__)
#define RX_BYTE_AVAILABLE USART_RX_vect
#define TX_FRAME_ENDED USART_TX_vect
#define TX_DATA_REGISTER_EMPTY USART_UDRE_vect
// Interrupt vectors for Atmega644
#elif defined(__AVR_ATmega644P__)
#define RX_BYTE_AVAILABLE USART0_RX_vect
#define TX_FRAME_ENDED USART0_TX_vect
#define TX_DATA_REGISTER_EMPTY USART0_UDRE_vect
#endif

/* I/O port containing the pin to be used as TX_ENABLE for the RS-485 driver */
static volatile uint8_t* TX_ENABLE_PORT = NULL;

/** Pin from the I/O port to be used as TX_ENABLE for the RS-485 driver */
static volatile uint8_t TX_ENABLE_PIN = 0;

ISR(RX_BYTE_AVAILABLE)
{
// Read the status and RX registers.
uint8_t status = UCSR0A;
// Framing error - treat as EOF.
if (status & _BV(FE0)) {
/* TODO: increment statistics */
}
// Overrun or parity error.
if (status & (_BV(DOR0) | _BV(UPE0))) {
/* TODO: increment statistics */
}
ringbuffer_write_byte(&rxrb, UDR0);
}

ISR(TX_FRAME_ENDED)
{
/* The end of frame interrupt will be enabled only when in RS-485 mode, so
* there is no need to test, just turn off the TX_ENABLE pin */
*TX_ENABLE_PORT &= ~_BV(TX_ENABLE_PIN);
}

ISR(TX_DATA_REGISTER_EMPTY)
{
uint8_t byte;

if (!ringbuffer_read_byte(&txrb, &byte)) {
/* If RS-485 is enabled, sets TX_ENABLE high */
if (TX_ENABLE_PORT)
*TX_ENABLE_PORT |= _BV(TX_ENABLE_PIN);
UDR0 = byte;
}
else {
/* No more chars to be read from ringbuffer, disables empty
* data register interrupt */
UCSR0B &= ~_BV(UDRIE0);
}
}

void uart_drv_start(uint8_t ubrrh, uint8_t ubrrl, uint8_t use2x,
volatile uint8_t* rs485_tx_enable_io_port,
uint8_t rs485_tx_enable_io_pin)
{
/* Initializes TX and RX ring buffers */
ringbuffer_init(&txrb, &tx_buffer[0], UART_TX_BUFSIZE);
ringbuffer_init(&rxrb, &rx_buffer[0], UART_RX_BUFSIZE);

cli();

/* Disables UART */
UCSR0B = 0x00;

/* Initializes baud rate */
UBRR0H = ubrrh;
UBRR0L = ubrrl;
if (use2x)
UCSR0A |= _BV(U2X0);
else
UCSR0A &= ~_BV(U2X0);

/* Configures async 8N1 operation */
UCSR0C = _BV(UCSZ00) | _BV(UCSZ01);

/* If a port was specified for a pin to be used as a RS-485 driver TX_ENABLE,
* configures the pin as output and enables the TX data register empty
* interrupt so it gets disabled in the end of transmission */
if (rs485_tx_enable_io_port) {
TX_ENABLE_PORT = rs485_tx_enable_io_port;
TX_ENABLE_PIN = rs485_tx_enable_io_pin;

/* Configures the RS-485 driver as an output (on the datasheet the data
* direction register is always on the byte preceding the I/O port addr) */
*(TX_ENABLE_PORT-1) |= _BV(TX_ENABLE_PIN);

/* Clears TX_ENABLE pin (active high) */
*TX_ENABLE_PORT &= ~_BV(TX_ENABLE_PIN);

/* Enables end of transmission interrupt */
UCSR0B = _BV(TXCIE0);
}
/* Enables receptor, transmitter and RX complete interrupts */
UCSR0B |= _BV(RXEN0) | _BV(TXEN0) | _BV(RXCIE0);

sei();
}

void uart_drv_send_byte(uint8_t byte, FILE *stream)
{
if (byte == '
') {
uart_drv_send_byte('
', stream);
}
uint8_t sreg = SREG;
cli();

/* Write byte to the ring buffer, blocking while it is full */
while(ringbuffer_write_byte(&txrb, byte)) {
/* Enable interrupts to allow emptying a full buffer */
SREG = sreg;
_NOP();
sreg = SREG;
cli();
}

/* Enables empty data register interrupt */
UCSR0B |= _BV(UDRIE0);
SREG = sreg;
}

uint8_t uart_drv_read_byte(FILE *stream)
{
uint8_t byte;
uint8_t sreg = SREG;
cli();
ringbuffer_read_byte(&rxrb, &byte);
SREG = sreg;
return byte;
}