' Sample COM port Interrupt Service Routine
' using MMBasic v5.2 by Geoff Graham
' Doug Pankhurst 2016
' The example below is designed to be an interrupt driven routine
' to handle a serial stream received by the Micromite of fixed length
' at regular or semi regular intervals. In this case, 14 characters every 2 secs.
' As we know "14 characters every 2 sec", when a receive interrupt is triggered,
' we need to ensure that all 14 characters have been received before reading
' the Rx buffer, so we trigger the interrupt after 14 characters received
' For the purposes of the test, put a jumper between COM1 Tx and Rx to
' loop the characters sent back into the receive input.

' If you don't know how many characters and/or how often, it is more complex
' and I will do some code for that later.

' Lets setup and define variables
option explicit
dim Tx_test$ = "Hello World." ' test string to transmit
dim Rx_test$ ' string to hold received data
dim Rx_Flag = 0 ' 1 means data received by Rx interrupt service routine,
' 0 means nother received yet
dim Rx_data_good_Flag = 0 ' Rx data length flag - if 1, Rx data error



' Now we need to set up some code to send a serial stream out the COM1 Tx port
' at 9600 baud every two seconds to test the Rx interrupt code.
settick 2000,Tx_Int ' every seconds, generate an interrupt that will send
' the characters Hello World. out the COM1 port

open "COM1:9600, 30, Rx_Int, 14" as #1 ' set up COM1 as our serial I/O
' Note we are specifying 9600 baud with a 30 character buffer (the default
' is 256), the name of the Rx interrupt service routine and importantly,
' the number of characters in the Rx buffer before the interrupt will be triggered.

' ******
' This will be our main program loop - it can be anything you want but in this
' case it just checks a flag that is set by the receive interrupt service routine
' to see whether any characters have been received
Main: ' just a label
print "Program to demonstrate COM1 receive interrupt service"
do
' anything you like in here - this is where all your actual data processing and
' display output goes
' in here somewhere, you would check the Rx_Flag to check if receive data
' is available to use
' eg.
If Rx_Flag = 1 then
print time$," Data Received: ",Rx_test$
Rx_Flag = 0 ' clear ready for next test
if Rx_data_good_Flag = 0 then
print "Rx data good."
else
print "Receive data error"
' if needed, handle the data error here
endif
endif
' other code as desired
loop

' ***** main program code end

'***** Subroutines *******
'*** the all important Rx interrupt service routine
sub Rx_Int ' the receive interrupt has occured
' at this point we know two things; we have received data and there are 14 characters
' waiting in the Rx buffer, so set the Rx data flag and read the data.
' That is all we need to do in here - get in, set the flag, get the data, get out!
Rx_Flag = 1
Rx_test$ = input$(30,#1) 'we will try to read 30 characters just to ensure
' the buffer is empty. If there are only 14 characters
' then that is how many will be read
' Note that the input buffer is now empty - the data is
' in Rx_test$
Rx_data_good_Flag = 0 ' clear flag ready for test
If len(Rx_test$) <> 14 then
Rx_data_good_Flag = 1 ' check how many characters actually read - if more than 14
' then there is a receive data problem
' - if you wanted, you could include a checksum in the Tx
' data sent and test it here
endif
' the sub routine will return with data in Rx_test$, Rx_Flag set and
' Rx_data_good_Flag clear if data length correct ( a very simple error check)
end sub

'


' Set Tick timer interrupt service routine, called every second
sub Tx_Int
Rx_Flag = 0 ' clear the Rx flag ready for the Rx interrupt to set it later
print #1,Tx_test$ ' just send the test string with CR LF at the end
' - 14 characters in all. Note that these
' characters will go out at MMBasic instruction speed
' to the Tx buffer - about 20uSec at which time the subroutine
' will return but actual transmit
' speed out the COM port will be 14mSec
end sub