i am hoping to let my arduino wait for an x amount of time, and if x time is up, the mcu will send a message.
or, if the message were to arrive anytime during x time, the mcu will send the message.
is there some method i can use? delay is not going to work here..
Use millis().
Pseudo code:
timestamp = now
Repeat
{
if message received or (millis - timestamp)>interval
{
send message
}
}
timestamp = now
Repeat
{
if message received or (millis - timestamp)>interval
{
send message
}
}
Yes, like that. I would add a "break;" after sending the message so the Repeat loop doesn't continue forever. 
also have to clear the "message received" flag, and have a way to reset the timestamp.
My android app is going to send a stream of bytes, 2 byte at a time.
The arduino is to receive them 2 byte at a time, and reply "w" when it receives them, telling android to send then next 2.
The problem i got it that sometimes, the stream pauses due to android not receiving a "w", as "w" might be sent during the times the Android might be processing the next byte, and flags in there were reset, ignoring the "w" received.
So I want to let the arduino, whenever the serial buffer is 0, to
1)send a "w"
2)send a "w" again, after 1millisecond, if no response is received.
Is this the right way to do it?
unsigned long Timer;
unsigned long inteval = 1;
while( s0 != '|' || s1 != '|' ){//terminates if '|' is received
if(s0 == '|' || s1 == '|')break;
else if(HWSERIAL.available() == 0){
HWSERIAL.print("w");//tell Android to send next byte
Timer = millis();
if(HWSERIAL.available() == 0 && millis() - Timer > 1){
HWSERIAL.print("w");//tell Android to send next byte
}
}
else if(HWSERIAL.available() >= 2) {
s0=HWSERIAL.read();
s1=HWSERIAL.read();
<some IO operations>
while( s0 != '|' || s1 != '|' ){//terminates if '|' is received
This will only stop the loop when you receive "||", not a single "|" as the comment suggests. So one of the two is wrong and needs to be corrected.
if(HWSERIAL.available() == 0 && millis() - Timer > 1){
You should also seriously look into why the message gets lost, as that shouldn't happen to begin with. I bet that device of yours will have some kind of serial buffer.
wvmarle:
while( s0 != '|' || s1 != '|' ){//terminates if '|' is receivedThis will only stop the loop when you receive "||", not a single "|" as the comment suggests. So one of the two is wrong and needs to be corrected.
while( s0 != '|' || s1 != '|' ){//terminates if '|' is received
doesnt this mean the loop will run when s0 or s1 are not equal to '|'.
meaning, if either s0 or s1 is equals to '|' , it will stop?
if(HWSERIAL.available() == 0 && millis() - Timer > 1){You should also seriously look into why the message gets lost, as that shouldn't happen to begin with. I bet that device of yours will have some kind of serial buffer.
the "w" sent to android might've gotten lost while the flags are being set.
Android app: on thread 1: receives "w" sets its flag to true
on thread 2: processes and sends 2bytes to Arduino, set flag to false
Arduino: receives the 2 bytes, replies with "w", wait for next 2 bytes.
on multiple occasions, the stream stops completely. and i cant make the arduino keep sending "w" without some sort of control. the Android app will crash due to too many internal broadcasts(broadcast is sent whenever incoming message).
tzijie:
while( s0 != '|' || s1 != '|' ){//terminates if '|' is receiveddoesnt this mean the loop will run when s0 or s1 are not equal to '|'.
meaning, if either s0 or s1 is equals to '|' , it will stop?
No - if either s1 or s1 is not equal to '|' the loop runs, it will only stop when both s0 and s1 equal '|'.
If you want it to stop when either equals '|' you have to use the logical and operator - then the loop runs if both are not equal to '|':
while( s0 != '|' && s1 != '|' ){ // terminates when a '|' is received in either s0 or s1
Be aware that now you will lose the information in s0 when s1 equals '|'.