I am sure u used delay in your code.
Nope, I dont use delays when sending or receiving the hex string.
I have flags in the android app, when a byte(hex representation) is sent out, android will only send the next byte when the Arduino responses with the same hex string. this is to ensure there are no data loss. about 1 out of 50 messages sent by android over BLE will somehow be lost. by lost, i mean android debug shows it is sent out, but arduino does not receive anything.
For example if you want to send a 1 word string that has 1000 character, you cannot send all of the data and record it to sd card. What you do is , send data 20 character at a time by adding 2 character at the beginning and ending of that 20 character. Call this a batch. There will be 50 batch you have to send. Do this in for loop at android side and wait for a signal from arduino.
yeah, the serial buffer will be full and start discarding.
currently, my Android app sends 1 byte(2 hex character) at a time.
Once Arduino receives it, writes to sd card, and reply Android with the same 2 hex character to indicate it has received it.
perhaps i should increase the message sent to 30characters(half of serial buffer).
is it really necessary to wrap each 'batch'?
you need to increase baud rate if you are doing the transfer at 9600.
I am using 115200 for my Teensy++ 2.0 board. believe that is the max the BLE module(hm-10, grove BLE) can handle reliably
void writeToFileHex(){
byte recoverByte;
char s0,s1;
sd.remove("hexdump.bmp"); //remove existing file first
myFile = sd.open("hexdump.bmp", FILE_WRITE);
Serial.println("\nReceiving HexDump, terminates with '|': ");
HWSERIAL.print("q");Serial.println("\nSent q to Android."); //tell Android to send first byte
if (myFile) {
Serial.print("Writing HexDump to hexdump.bmp...");
Serial.println("\nReceived HexDump: ");
while( s0 != '|' && s1 != '|' ){
if(HWSERIAL.available() >= 2) {
s0=HWSERIAL.read();
s1=HWSERIAL.read();
if(s0 == '|' || s1 == '|'){
HWSERIAL.print("t");
Serial.print("| received. Sent t. break.");
break;
}
HWSERIAL.print(s0);HWSERIAL.print(s1); //send same hex chars back to android
Serial.print(s0);Serial.print(s1);
//convert the received hex char back to byte
recoverByte = (convertFromHex(s0) << 4) | (convertFromHex(s1));
myFile.write(recoverByte);
}
//the following is for when message sent by android is lost, tells android to resent previous message
if(HWSERIAL.available()==0){
Timer = millis();
while(HWSERIAL.available() == 0){
//HWSERIAL.print("w");Serial.print("w");//tell Android to send next byte
//Serial.println("s");
//if no response from android by 4 milliseconds, send another message.
if( millis() - Timer > 250){
if(s0 == '|' || s1 == '|'){
Serial.print("millis | break.");
break;
}
HWSERIAL.print("s");Serial.println("\nno response, sent s");//tell Android to send next byte
Serial.print(s0);Serial.print(s1);
Timer = millis();
}
}
}else{
Timer = 0;
}
}//while( s0 != '|' && s1 != '|' )
// close the file:
myFile.close();
Serial.println("\ndone.");
}
else {
// if the file didn't open, print an error:
Serial.println("error opening hexdump.bmp");
}
}