is unsigned char EXTERN-able? Linking problem...

Hi,

I have a program that calls Assembly from C. The odd behaviour is that one assembly function links fine, while the other gives me UNRESOLVED EXTERNAL SYMBOL and REFERENCE TO UNRESOLVED EXTERNAL (L1 and L2) warnings from the linker. both routines follow the exact same template, with the exception that the one that gives me the warnings passes paramaters. I would assume unsigned char is a valid type to pass to assembly via an extern declaration?!? Code fragments are below:

The C source calling the assembly routines:

#define MPU_READ_ADDR	0
...
void coInitReg();        // C protos
void xint_handler (void);

// these are assembly
extern void c_init(void);
extern unsigned char mpu_read(unsigned char);
...
void coInitReg()
{
    cinit();    // call assembly -> OK
    ...
}

void xint_handler(void)
{
    unsigned char address = MPU_READ_ADDR;
    ...
    mpu_data = mpu_read(address); // call assembly -> L1/L2 WARNING!
    ...
}

this is a fragment of the assembly:

PUBLIC c_init
PUBLIC mpu_read

...
; this one seems OK
UTILS	SEGMENT CODE
	RSEG UTILS
c_init:	mov R0,#13
        ...
        ret

; this one give me the L1 & L2 warnings!
MPU_RD	SEGMENT CODE
	RSEG MPU_RD

mpu_read:
	MOV A,R7	; put passed parameter from R7 in A
        JNZ rddata	; jump
        ...
        MOV R7,P2        ; into R7 for ret, as the compiler asks for
        ret
        ...

Any clues what the differences are that would create the linker warnings?

thanks

Jeff