Puzzled printf

kevin5k · Joined: 08 Jan 2007 Posts: 41

Hi everyone,

I am quite puzzled with my test file popping up errors that stdout is not defined. I am just trying to run a normal printf(). My code for this file is as follows:

RLScott · Joined: 10 Jul 2007 Posts: 465

kevin5k · Joined: 08 Jan 2007 Posts: 41

Guest · Posted: Thu Jun 05, 2008 9:08 pm

Yes, but you need to configure your RS232 port (which pins are used for input/output/baudrate).

Example:

#use rs232 (baud=9600, xmit=pin_B2,rcv=pin_B1)

defines baud rate @ 9600bps, output on B2 and input on B1.

Guest · Posted: Thu Jun 05, 2008 11:17 pm

Wayne_ · Joined: 10 Oct 2007 Posts: 681

LOL

When you say locally what are you refering to ?
Do you have an LCD display attached ?
How do you communicate with your display device (SPI, I2C, Serial, other) ?

If there is nothing connected that is capable of displaying an ASCII string then what is the point of having the printf in there ?

Ttelmah · Guest

Think about it for a moment.

In 'C' (the original K&R implementation), you were writing code that ran _inside_ an 'operating system'. This had basic operations being performed, for 'standard input' (the keyboard), and 'standard output'. There was also the idea that the output, could be redirected by the OS (pipe operations), so there was a 'standard error' output, that bypassed this.

Now, with CCS, you are writing code inside a chip, that has no such operating system. As such, _you_ have to provide the input and output code. CCS offers a 'default' way of doing this, where if a #USE_RS232 line is present, the last one defined, is treated as providing the standard IO. If you want instead to route to something else (you have a local LCD for example), then you have to write the output function for this (the default with the CCS LCD code, is 'lcd_putc'), and tell 'printf', to talk to _this_, rather than the 'stdio'. So:

printf(lcd_putc,"What you want to print");

The key point to understand, is that there is no 'OS' outside your code, to display stuff, or get stuff, and by some method or other, _you_ must provide the functions for this.

Best Wishes