Problem in macro value generation

[LBdgWgt]

Hi all,

i am using C30 compiler for dsPIC30 (i think it basically gcc right?)
i have a problem as i tried to make automatic macro value generation for UART baud rate register.

#define XTAL                7500000U
#define PLL_MULTIPLIER      8U
#define CLOCK_POSTSCALER    1U
#define F_OSC               (XTAL * PLL_MULTIPLIER)/CLOCK_POSTSCALER
#define FCY                 F_OSC/4U
#define UART_BAUD           9600U
#define UART1_BRG           (FCY/(16U * UART_BAUD) - 1U)

it should be that the result i want:

UART1BRG = (UINT16) ((7.5M*8/4)/(16*9600)) - 1 = 97 (approximately)

but what as i generate the code, the baud register is always filled with the value of 0x298 (664 decimal)?

thanks for any hints!

 

[LBdgWgt]

found the solution:

#define XTAL                7500000UL
#define PLL_MULTIPLIER      16UL
#define CLOCK_POSTSCALER    1UL
#define F_OSC               ((XTAL * PLL_MULTIPLIER)/CLOCK_POSTSCALER)
#define FCY                 (F_OSC/4UL)
#define UART_BAUD           9600UL
#define UART1_BRG           (UINT16) ((FCY/(16UL * UART_BAUD)) - 1UL)

seems we have to use the brackets and UL for big numbers such as 7500000 in my case

regards,

 

[btbass]

Yes, the C30 compiler is a port of the Gcc compiler.
and a very nice compiler it is too!
Macros have been depreciated and thier use is discouraged, except for simple text sustitutions.
if we expand your macro UART1_BRG we get:

(UINT16) (((((7500000UL * 16UL)/1UL)/4UL)/(16UL * 9600UL)) - 1UL)

Quite easy to miss a braket and end up with the wrong value?