DFPlayer Mini MP3 Module Controlling Using AVR UART Codevision Sample: http://blog.allii.ir/2016/01/dfplayer-mini-mp3-module-control-avr-uart/

dfplayer_mini_avr.c

/************************************************************************************
  Run DFPlayer Mini Module With Atmega8
  DFPlayer Mini: http://blog.allii.ir/go/dfplayer-mini-main-wiki/
  For: http://blog.allii.ir/2016/01/dfplayer-mini-mp3-module-control-avr-uart/
  By: Alireza Dabiri Nejad | http://blog.allii.ir 
  
  Program:                : Codevision
  Chip type               : ATmega8
  AVR Core Clock frequency: 8/001000 MHz
*************************************************************************************/

/* MCU Define */
#include <mega8.h>
/* Include I/o Functions */
#include <stdio.h>
#include <stdlib.h>

int default_buffer[10] = {0x7E , 0xFF , 0x06 , 0x00 , 0x00 , 0x00 , 0x00 , 0xEF}; // Default Buffer
int buffer_data[10] = {0x7E , 0xFF , 0x06 , 0x00 , 0x00 , 0x00 , 0x00 , 0xEF}; // Sending Buffer

// Send Buffer to UART TX Pin
void send_buffer(void) {
    int i;
    for( i=0; i< 10; i++){
        putchar(buffer_data[i]);
        buffer_data[i] = default_buffer[i];
    } 
}

// Set Volume And Send it's Serial Command
void set_volume( int volume ) {
    buffer_data[3] = 0x06;
    buffer_data[6] = volume;
    send_buffer();     
}

// Set a Track (1-3000) to Play
void play_track(int track_id) {
  buffer_data[3] = 0x03;
  if(track_id < 256) {
    buffer_data[6] = track_id;
  } else {
    buffer_data[5] = track_id / 256;
    buffer_data[6] = track_id - 256 * buffer_data[6];
  }
    send_buffer();
}

// Set a Folder (1-255) and Track (1-255) to Play
void play_track(int folder_id, int track_id) {
  buffer_data[3] = 0x0F;
  buffer_data[5] = folder_id;
  buffer_data[6] = track_id;
  send_buffer();
}

// Set a Track to Play Continuous
void play_current_track_continuous(void) {
    buffer_data[3] = 0x08;
    buffer_data[6] = current_track_number;
    send_buffer();
}

// Pause Current Playing Track
void pause_current_track() {
    buffer_data[3] = 0x0E;
    send_buffer(); 
}

void main(void)
{
  // USART initialization
  // Communication Parameters: 8 Data, 1 Stop, No Parity
  // USART Receiver: Off
  // USART Transmitter: On
  // USART Mode: Asynchronous
  // USART Baud Rate: 9600
  UCSRA=0x00;
  UCSRB=0x08;
  UCSRC=0x86;
  UBRRH=0x00;
  UBRRL=0x33;
  
  while(1) {
    
  }
}

dfplayer_mini_avr.txt

$S Ver. Number Command Feedback Param_MSB Param_LSB Check_MSB Check_LSB $O // UART Send Command Format
7E FF 06 09 00 00 02 FF F0 EF // Set microSD Command With Checksum
Checksum = ~(Ver.+Number+Command+Feedback+Param_MSB+Param_LSB) + 1 // Checksum Calculation Formula