[U-Boot] LPC3250 NAND settings

I use a board based on LPC3250 which is supported by u-boot 1.3.3.

u-boot, kernel, and rootfs reside in NAND FLASH memory.

I want to improve boot time. u-boot utilizes NAND memory by setting the timing parameters as

SLCNAND->slc_tac = (SLCTAC_WDR(14) | SLCTAC_WWIDTH(9) | SLCTAC_WHOLD(3) | SLCTAC_WSETUP(4) | SLCTAC_RDR(14) | SLCTAC_RWIDTH(9) | SLCTAC_RHOLD(3) | SLCTAC_RSETUP(4));

By changing these settings, at best u-boot approximately takes 6 seconds to finish, then kernel starts.

Is there any method to boot faster from flash? I know u-boot 1.3.3 is now obsolete but I have to use it.

abdullah