Printf() size, questions?

#pragma maxargs (20) will set the number of bytes used by variable arg. functions such as printf to 20. The default for the small model is 15, for the large 40. See page 34 of the latest C51 v6.02 C51.pdf manual.

Mapping printf to any device is simple. First, write your own putchar(). One that can print to either UART based upon some file static var. This will automatically replace the library version. Then, write a device switcher function that controls the file static var. that putchar uses to determine which UART to use. Printf will use what ever function has the name putchar.

- Mark

#pragma maxargs (20) will set the number of bytes used by variable arg. functions such as printf to 20. The default for the small model is 15, for the large 40. See page 34 of the latest C51 v6.02 C51.pdf manual.

Mapping printf to any device is simple. First, write your own putchar(). One that can print to either UART based upon some file static var. This will automatically replace the library version. Then, write a device switcher function that controls the file static var. that putchar uses to determine which UART to use. Printf will use what ever function has the name putchar.

- Mark

Thanks Mark. But also, how much space will the function take? I've
heard people say that printf() may take up to 2K of code space. Meaning
that if printf() is used in the embedded application, then 2K of code
space will be eaten up. If thats the case then I'll have to come up
with my own transmission mechanism.

Oh goodness yes, printf is fat. Just build a small file with only main() and no printf call and note the size of the code in the .m51. Then make a call to printf in this file, build and check the .m51 file again. This will tell you the size of printf for a given model.

For protocols I'd skip printf. I always use some variant of:

STX | message class | class subtype | body | checksum

void sendPacket(Major maj, Minor min, char *pBody, U8 bodyLen)
{
    U8 idx;
    U8 checksum;

    putchar(STX);
    checksum  = STX;
    checksum += putEscapedChar(maj);
    checksum += putEscapedChar(min);
    checksum += putEscapedChar(bodyLen);
    checksum += putEscapedChar(~bodyLen);

    for (idx = 0; idx < bodyLen; ++idx)
    {
        checksum += putEscapedChar(*pBody++);
    }
    
    putEscapedChar(checksum);
}

would please tell me more about the folloing function:
putEscapedChar(checksum)

I'd write my own putchar() like this:

char putchar(char outChar)
{
    TI   = 0;
    SBUF = outChar;
    while (!TI);
    return outChar;
}

void putFiltByte(U8 outByte)
{
    if (STX == outByte || DLE == outByte)
    {
        // Escape this data char.
        putchar(DLE);

        // Ensure this data char. is never an STX or DLE.
        outByte += ' ';
    }

    putchar(outByte);
}

So I just have to have a putchar() somewhere in my code and this will
automatically override the putchar() that printf() uses? And if I decide
not to use printf() can I override the interrupts for UART transmit
and receive the same way? Also, I need to prove my code works
using the uVision2 simulator because we won't have a prototype for
some time.

Again, I'm using the uVision2 eval simulator. When I try to see code size
it doesn't appear to include the size of printf(). In fact it just tells
me the starting location of my functions but not the sizes. Is there
a way to list the code and data sizes of objects? Also, even at the
end of the .m51 file, the total code size does not seem to include the
size of the printf() function. Is this because of the simulator?

I just compiled and linked the HELLO example project. The following excerpt from the MAP file (*.m51) lists the starting location and sizes of the modules inthe program.

LINK MAP OF MODULE:  Hello (HELLO)


            TYPE    BASE      LENGTH    RELOCATION   SEGMENT NAME
            -----------------------------------------------------

            * * * * * * *   D A T A   M E M O R Y   * * * * * * *
            REG     0000H     0008H     ABSOLUTE     "REG BANK 0"
            DATA    0008H     0014H     UNIT         _DATA_GROUP_
                    001CH     0004H                  *** GAP ***
            BIT     0020H.0   0001H.1   UNIT         _BIT_GROUP_
                    0021H.1   0000H.7                *** GAP ***
            IDATA   0022H     0001H     UNIT         ?STACK

            * * * * * * *   C O D E   M E M O R Y   * * * * * * *
            CODE    0000H     0003H     ABSOLUTE     
            CODE    0003H     035CH     UNIT         ?PR?PRINTF?PRINTF
            CODE    035FH     008EH     UNIT         ?C?LIB_CODE
            CODE    03EDH     0027H     UNIT         ?PR?PUTCHAR?PUTCHAR
            CODE    0414H     001BH     UNIT         ?PR?MAIN?HELLO
            CODE    042FH     000DH     UNIT         ?CO?HELLO
            CODE    043CH     000CH     UNIT         ?C_C51STARTUP

So I just have to have a putchar() somewhere in my code and this will
automatically override the putchar() that printf() uses?

Yes, of course. Same for getchar().

And if I decide not to use printf() can I override the interrupts for UART transmit and receive the same way?

You can use interrupts with or without printf() being used. It's up to how you implement putchar and getchar. Either way, you are not overriding the interrupts. In a uC you are in complete control. Interrupts are not used by the default putchar/getchar supplied by Keil.

Also, I need to prove my code works using the uVision2 simulator because we won't have a prototype for some time.

I can't help you there. I always use an In-Circuit Emulator on a simple board with a RS-232 driver.

- Mark

Again, I'm using the uVision2 eval simulator. When I try to see code size
it doesn't appear to include the size of printf(). In fact it just tells
me the starting location of my functions but not the sizes. Is there
a way to list the code and data sizes of objects? Also, even at the
end of the .m51 file, the total code size does not seem to include the
size of the printf() function. Is this because of the simulator?

Just look in the .m51 file for a simple foo.c file compiled and linked, don't use your big project for this. Build the file without using printf, check the total size. Then add one call to printf, check the size again. The simulator has nothing to do with the linker output file (.m51).

- Mark

CODE    0003H     035CH     UNIT         ?PR?PRINTF?PRINTF