Why Arduino fails to receive ACK signal?

import serial from time import sleep import base64 def ACK(): ser.write(0x06) ser.write(0xD) ser.write(0xA) ser = serial.Serial('/dev/ttyACM0', baudrate=9600, timeout=1) if not ser.isOpen(): ser.open() print("OPEN Serial\n") print("READ DATA\n") while 1: ACK() line = ser.readline() if(line == b""): continue; if(line[:1] == b'2'): print("DATA:") print(line) print("####") 

#define LASTBLOCK 1023 #define LASTPAGE 63 #define LASTBYTE 2111 #define PAGE_READ 0x13 #define PAGE_READ_CACHE_SEQUENCIAL 0x03 #define READ_FROM_CACHE 0x3B #define PAGE_READ_CACHE_END 0x3F #define PAGE_SIZE 2111 #define BUFFER_LEN 32 #define ACK 0x06 #define NACK 0x06 unsigned int page_to_read = 1; unsigned int block_to_read = 1; boolean spi_begun = false; uint8_t bytes_index = 1; typedef struct { // Page that is transmitted unsigned int page; // Block that is transmitted unsigned int block; // A mumeric representation of the 32 byte segment that I send. // I cannot send the page altogether, therefore a byte intexing is required uint8_t bytes_index; // Despite my buffer is 32 bytes the usable data may be less uint8_t length; // Data buffer containing the data to be sent via serial byte data[BUFFER_LEN]; } usb_msg; void sendMsg(usb_msg msg){ byte* ptr = (byte*)&msg; Serial.print(0x02); for (size_t i = 0; i < sizeof(usb_msg); i++){ Serial.print(*ptr >>4, HEX); Serial.print(*ptr & 0x0F, HEX); ptr++; } Serial.print(0x03); Serial.println(); } bool clientAck() { uint8_t incomingByte = NULL; digitalWrite(13,HIGH); do { uint8_t incomingByte = Serial.read(); } while(incomingByte!=ACK); digitalWrite(13,LOW); } void setup() { Serial.begin(9600); pinMode(13,OUTPUT); } void loop() { // I need to reset the counts before reading any block if(page_to_read > LASTPAGE){ page_to_read = 1; block_to_read ++; } if(block_to_read > LASTBLOCK){ spi_begun=false; return ; } if(!spi_begun){ spi_begun=true; } clientAck(); // Reading page there's no need for seperate function in order to avoid stack usage for(int bytes_to_read = PAGE_SIZE; bytes_to_read > 0; bytes_to_read-=BUFFER_LEN){ uint8_t bytes_to_send = bytes_to_read < BUFFER_LEN ? bytes_to_read: BUFFER_LEN; usb_msg msg = {page_to_read, block_to_read, bytes_index, bytes_to_send, {1, 1, 1, 1, 1, 1, 1, 1, 1, 1}}; sendMsg(msg); delay(100); bytes_index++; } page_to_read++; delay(100); }