Subj : Need to write putchar for embedded system
To   : comp.lang.c,comp.programming
From : Confused User
Date : Thu Jun 30 2005 10:29 pm

I am working on device that utilizes a Motorola 68HC16 microcontroller. I am
using an old unsupported piece of crap Whitesmith's / Intermetrics / Tasking
compiler. The embedded compiler business was quite insestual for while
wasn't it? I need to write putchar so that printf can function properly.

Anyway, the compiler comes with just a shell of a putchar routine. It
literally returns the character you passed to it and nothing else. That is
not why it's a piece of crap, although they could have at least supplied
something that writes to the serial port.

So, I already have a serial port interrupt routing with circular buffers
(in/out) and a function call (SendData()) that copies a data from a pointer
argument and manages the circular buffer. So, I want to have my putchar
routine call SendData.

I noticed from looking around that putchar returns EOF if unsuccessful. EOF
is defined as -1 in the compiler header file. Therefore, it occurs to me
that putchar can only be used for ASCII data. This is OK, I just need to
make sure I have that right. Because, binary data could include -1 right?
That means I should never use it alone to send binary data. If so, is this
true for the PC? After all, it's counterpart, getchar retrives binary scan
codes from the keyboard unless they have already been converted to ASCII
characters before they get to that level.

I would guess the only time getchar should return EOF is if the transmit
buffer is full. My SendData() function already is set to return a fail code
if the buffer is full. putchar can pass this on to printf (of course I have
to change SendData() to use EOF as a fail code).

As an embedded programmer, I am not real familiar with what normal pass/fail
return codes should be. The high level languages were developed around full
OS systems (Unix etc.) and then seem to have migrated to the embedded world
leaving some us without familiarity of conventions.

Enough rambling.... Just looking for any constructive input.

Elvis

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