我正在将ATTINY85 MCU与2线从模式的USI一起使用。使用i2cdetect和i2cset之类的Linux工具，我已经使用RPi4验证了以下内容：

• i2cdetect在0x05地址i2cdetect -y 1上检测到设备
• 设备正确发送了ACK位
• i2cset在写入期间未显示错误迹象：i2cset -y 1 0x05 0x01

我想帮助您弄清楚为什么USIDR没有将0x01返回到我的LED变量，从而打开/关闭LED

#define F_CPU 8000000UL
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>

typedef enum
{
    ADDRESS_MATCH = 0x00,READ_DATA     = 0x01,SEND_ACK      = 0x02,} USI_State_t;

volatile USI_State_t state;
volatile int8_t LED;

int main(void)
{
    PORTB |= (1<<PB0) | (1<<PB2);   //PB0=SDA,PB2 = SCL
    DDRB &= ~(1<<PB0) | ~(1<<PB2);
    DDRB |= (1<<PB4);

    USICR = (1<<USISIF) | (0<<USIOIF) | (1<<USIWM1) | (0<<USIWM0) | (1<<USICS1) | (0<<USICS0) | (0<<USICLK) | (0<<USITC);
    USISR = (1<<USISIF) | (1<<USIOIF) | (1<<USIPF) | (1<<USIDC) | 0x00;

    sei();
    while (1) 
    {
        if (LED != (int8_t)0x00) PORTB |= (1<<PB4);
        else PORTB &= ~(1<<PB4);
    }
}

ISR(USI_START_vect)
{
    DDRB &= ~(1<<PB0);

    while ((PINB & (1<<PB2)) && !(PINB & (1<<PB0)));

    if (!(PINB & (1<<PB0)))
    {
        USICR = (1<<USISIF) | (1<<USIOIF) | (1<<USIWM1) | (1<<USIWM0) | (1<<USICS1) | (0<<USICS0) | (0<<USICLK) | (0<<USITC);
    }
    else USICR = (1<<USISIF) | (0<<USIOIF) | (1<<USIWM1) | (0<<USIWM0) | (1<<USICS1) | (0<<USICS0) | (0<<USICLK) | (0<<USITC);

    state = ADDRESS_MATCH;
    USISR = (1<<USISIF) | (1<<USIOIF) | (1<<USIPF) | (1<<USIDC) | 0x00;
}

ISR(USI_OVF_vect)
{
    switch (state)
    {
        case ADDRESS_MATCH:
            if ((USIDR>>1) != 0x05)
            {
                DDRB &= ~(1<<PB0);
                USICR = (1<<USISIF) | (0<<USIOIF) | (1<<USIWM1) | (0<<USIWM0) | (1<<USICS1) | (0<<USICS0) | (0<<USICLK) | (0<<USITC);
                USISR = (1<<USISIF) | (1<<USIOIF) | (1<<USIPF) | (1<<USIDC) | 0x00;
            }
            else
            {
                state = READ_DATA;
                USIDR = 0x00;
                DDRB |= (1<<PB0);
                USISR = (0<<USISIF) | (1<<USIOIF) | (1<<USIPF) | (1<<USIDC) | 0x0E;
            }
            break;

        case READ_DATA:
            DDRB &= ~(1<<PB0);
            state = SEND_ACK;
            USISR = (0<<USISIF) | (1<<USIOIF) | (1<<USIPF) | (1<<USIDC) | 0x00;
            break;

        case SEND_ACK:
            LED = (int8_t)USIDR;
            USIDR = 0x0;
            DDRB |= (1<<PB0);
            USISR = (0<<USISIF) | (1<<USIOIF) | (1<<USIPF) | (1<<USIDC) | 0x0E;
            break;
    }
}

LED变量设置为switch语句SEND_ACK内部的值。任何帮助将不胜感激！