dm365 GIO81 not work.

hi guys:

in uboot ( from DVSDK4.0 ) I want to set FIELD as a GPIO (GIO81), but it doesnot work:

writel((readl(PINMUX1) & (~(3<<18))), PINMUX1);

gpiobank_base =(struct davinci_gpio *)DAVINCI_GPIO_BANK45;

tmp = readl(&gpiobank_base->out_data);

tmp |= (1<<17); //set GIO81=1

writel(tmp, &gpiobank_base->out_data);

printf("pinmux1=0x%08x,out_data=0x%08x\n",readl(PINMUX1),tmp);

I have used other GPIO , like GIO50/51/42, they work!! But GIO81 does not work , I don't know why , The datasheet is wrong about PINMUX1?