ADSP-21479 fails to boot from spi flash

Hi all,
I design a board with ADSP-21479 LQFP100 (silicon 0.2). Three M25P16 flash chips are connected to the DSP using default SRU2 routing, with SPI_FLG0-2 as chip select signals, respectively. The one with SPI_FLG 0 is used as booting device. It fails to boot.
I can use the flash programmer for 21479 EZ-Board to identify the boot flash device, program and verify without problem. The loader is "spi flash", hex format.
When Viewed with oscilloscope when the board powers up, I can see the SPI_CLK and a continously low SPI_FLG0 since the first SPI_CLK pulse. Only one high pulse after SPL_FLG0 pulled low on MOSI is observed, and the MISO signal remains high all the time.
I attached the waveforms from the oscilloscope. I would be appreciate if anyone here can figure out my problem. Thanks!