Sorry - I meant <enable> assembler interrupt routines from C.
I have a working I2C routine in assembler:-

PUBLIC I2C_ISR
I2C_ISR:
.....
RETI

In the C module I have:-
EXTERN void I2C_ISR(void); // prototype

void I2C_ISR(void) interrupt 7 using 1
{
I2C_ISR();
}

Is this correct? It seems to work