HOW to MAKE PWM wave in RZ/A2M

Hello I am developing based on FREERTOS using RZ/A2M.

I need PWM function for magnetic buzzer and lcd BACKLIGHT unit.

so I am proceeding according to the procedure of GPT driver guide document.

In Document suggest 3 step.

1. setting in smart configurator.

2. open driver 

3. contol command : CTL_GPT_PWM_SAW_START_CHANNEL

But PWM waveform not generate.

below my code: 

s_gpt_handle = open(DEVICE_INDENTIFIER "gpt_pwm_saw4", O_RDWR);
gpt_err=control(s_gpt_handle, CTL_GPT_PWM_SAW_START_CHANNEL, NULL); 

how can I get solution

help me.