MS522低功耗寻卡

方案：单片机处于低功耗模式，ms522处于软掉电模式。单片机用rtc定时（比如每隔1s）唤醒，单片机唤醒后唤醒ms522寻卡。寻到卡则做进一步处理，否则ms522继续进入软掉电模式，单片机进入低功耗模式。

if (1 == flag_rtc_wakeup)
{
    flag_rtc_wakeup = 0;
 
    pcd_soft_powerup();

    if (pcd_fast_detect() == true)
    {
        //todo
    }

    pcd_soft_powerdown();
}

void pcd_soft_powerdown(void)
{
    write_rawrc(commandreg, pcd_nocmdchange | (1 << 4));
}

void pcd_soft_powerup(void)
{
    uint8_t count = 0;

    write_rawrc(commandreg, pcd_nocmdchange & (~(1 << 4)));
    do
    {
        // wait for the powerdown bit in commandreg to be cleared (max 3x10us)
        delay_10us(1);
    } while ((read_rawrc(commandreg) & (1 << 4)) && (++count) < 3);
}

手册相关内容

//快速寻卡函数
bool pcd_fast_detect(void)
{
    uint8_t valid_bits = 7;
    uint8_t command = picc_reqidl;
    uint8_t wait_irq = 0x30; // rxirq and idleirq
    uint8_t n;
    uint16_t i;

    clear_bit_mask(collreg, 0x80); // valuesaftercoll=1 => bits received after collision are cleared.

    // write_rawrc(commandreg, pcd_idle);    // stop any active command.
    write_rawrc(comirqreg, 0x7f);            // clear all seven interrupt request bits
    set_bit_mask(fifolevelreg, 0x80);        // flushbuffer = 1, fifo initialization
    write_rawrc(fifodatareg, command);       // write senddata to the fifo
    write_rawrc(bitframingreg, valid_bits);  // bit adjustments
    write_rawrc(commandreg, pcd_transceive); // execute the command
    set_bit_mask(bitframingreg, 0x80);       // startsend=1, transmission of data starts

    i = 3; //根据时钟频率修改
    while (1)
    {
        n = read_rawrc(comirqreg); // comirqreg[7..0] bits are: set1 txirq rxirq idleirq hialertirq loalertirq errirq timerirq
        if (n & wait_irq)
        { // one of the interrupts that signal success has been set.
            //debug("t\r\n");
            break;
        }
        if (n & 0x01)
        { // timer interrupt - nothing received in time
            //debug("f\r\n");
            return false;
        }
        if (--i == 0)
        { // the emergency break. if all other conditions fail we will eventually terminate on this one. communication with the mfrc522 might be down.
            //debug("i\r\n");
            return false;
        }
    }

    return true;
}

void pcd_reset(void)
{
    rc522_rst_on;
    write_rawrc(commandreg, pcd_resetphase);
    uint8_t count = 0;
    do
    {
        // wait for the powerdown bit in commandreg to be cleared (max 3x40us)
        delay_10us(4);
    } while ((read_rawrc(commandreg) & (1 << 4)) && (++count) < 3);
    // tauto=1; timer starts automatically at the end of the transmission in all communication modes at all speeds.10us
    write_rawrc(tmodereg, 0x80);
    write_rawrc(tprescalerreg, 0x43); // 10μs
    // reload timer with 0x1e = 30, ie 0.3ms before timeout.
    write_rawrc(treloadregh, 0x00);
    write_rawrc(treloadregl, 0x1e);

    write_rawrc(txautoreg, 0x40);
    write_rawrc(modereg, 0x3d); //和mifare卡通讯，crc初始值0x6363

    pcd_antenna_on();
}

参考资料：

ms522手册：https://wenku.baidu.com/view/6f5bcabcbcd126fff6050b77

关于软掉电模式的讨论：

软掉电模式demo：https://github.com/akellai/rfid-music/blob/master/rfid_promini/rfid_promini.ino