outputting a character on the console from within hlasm (370)

Question

For fun I'm implementing brainfuck compilers translating bf to e.g. x86 assembly. Currently I'm working on bf to mainframe assembly. Dialect is "HLASM" and mainframe is one of IBM with a 370.

Sofar most of it works only emitting a character to the console of the operator fails: I only get spaces and it looks like an implicit linefeed is added (which I don't want).

Can anyone find my mistake?

* get a character to display
         LLGC  R6,0(R7)
* get a pointer to the buffer which will contain the char to displa
         LA    R5,BUFFER
* store character in buffer
         STC   R6,0(R5)
* get a pointer to the memory area describing the data to display
         LA    R1,MSGAREA
* invoke display char
         SVC   35

MSGAREA  EQU   *
         DC    AL2(5)
         DC    XL2'00'
BUFFER   DC    C'!'

Answer 1

I would suggest writing to the SYSOUT DD to give you the flexibility to run either in batch (allocating SYSOUT in your JCL) or interactively (allocating SYSOUT to the terminal session which I believe is the default in TSO).

[entry logic, initialization and so forth]
         OPEN  (SYSOUT,OUTPUT)
         
         PUT   SYSOUT,RECORD
         
         CLOSE SYSOUT
[exit logic]         
         
RECORD   DC    CL80' '   
SYSOUT   DCB   DDNAME=SYSOUT,                                          X
               DSORG=PS,                                               X
               MACRF=PM,                                               X
               RECFM=FB,                                               X
               LRECL=80

You might want to also look at the TPUT, TGET, and TPG macros for terminal I/O if you're okay with tying your program to running in TSO exclusively. Terminal I/O is kind of odd in a 3270 environment if you're used to streaming I/O as in Unix.

DCB is documented here. OPEN is documented here. PUT is documented here. CLOSE is documented here.