Example of stdin retargeting

Jonathan,

Here is my example, hope it helpful:

int _read (int fd, char *ptr, int len)
{
  int i;
  for (i=0; i < len; i++)
  {
    char ch = getkey();
        sendchar (ch);
        ptr[i] = ch;
        if (ch == '\r') break;
  }
  return i;
}

Joey,

I implemented my _read() very similar to the example you provided. In my application, I do the following:

char myString[32];
gets(myString);
printf(myString);

At the console, if I enter 'jon' and hit the return string, then _read() returns 3 (i == 3 on exit of this function). Is this correct? It excludes the carriage return character. Should the return value be 4?

Also, I am finding that gets() function call never returns. Somehow _read() is being called repeatedly. Why does this happen?

By the way, here is the toolchain version I'm using, in case that makes a difference:

arm-none-eabi-gcc (GNU Tools for ARM Embedded Processors) 4.7.3 20121207 (release) [ARM/embedded-4_7-branch revision 194305]
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Thanks,
JF

As I stated in my previous response, _read() is called repeatedly. If I return 0, from _read(), the application call to gets() will finally return.

After returning 0 from _read(), subsequent calls to gets() are not successful:
gets() returns immediately (does not filter down to _read()), and the return value from gets() is NULL.

So again, I wonder if there is a working example of _read()? What are the expected return values from the _read() function? How should this function behave for successful retargeting of stdin?

Thanks,
JF

Suggest debug your gets implementation. This doesn't seem to be a tools or
library issue to me.
On Nov 5, 2013 11:51 PM, "Jonathan Farmer" <
<email address hidden>> wrote:

> Question #238665 on GCC ARM Embedded changed:
> https://answers.launchpad.net/gcc-arm-embedded/+question/238665
>
> Jonathan Farmer gave more information on the question:
> As I stated in my previous response, _read() is called repeatedly. If I
> return 0, from _read(), the application call to gets() will finally
> return.
>
> --
> You received this question notification because you are an answer
> contact for GCC ARM Embedded.
>

'gets()' is not my implementation. This function is coming from stdio library, as provided by this toolchain. I have similar problems when using scanf().

So I still don't understand this stdin retargetting. What is needed to successfully implement _read()? How should this interface behave?

gets won't read from UART unless you have you UART operation implemented in _read. So don't call gets. Instead, implement your getkey() with UART IO operations.

I had the same behaviour. The problem was that I implemented _read blocking (waiting for input). When implemented with immediate return, it worked fine.