linux hangs after uncompress kernel image

[lily]

i work on octobusHPPC405EP board . when I try to bring up the kernel i meet the problem that linux hangs after uncompressing image:

U-Boot 1.1.2 (Jun  3 2005 - 12:05:48)

CPU:   IBM PowerPC 405EP Rev. B at 133.333 MHz (PLB=133, OPB=66, EBC=33 MHz)
       IIC Boot EEPROM disabled
       PCI async ext clock used, internal PCI arbiter enabled
       16 kB I-Cache 16 kB D-Cache
OCTOBUS Board: ### No HW ID - assuming OCTOBUS HPPC405
I2C:   ready
DRAM:  32 MB
FLASH:  4 MB

=>iminfo 1000000
## Checking Image at 01000000 ...
   Image Name:   Linux-2.4.21-pre5
   Created:      2005-08-03  17:45:20 UTC
   Image Type:   PowerPC Linux Kernel Image (gzip compressed)
   Data Size:    548345 Bytes = 535.5 kB
   Load Address: 00000000
   Entry Point:  00000000
   Verifying Checksum ... OK
=> bootm 1000000
## Booting image at 01000000 ...
   Image Name:   Linux-2.4.21-pre5
   Created:      2005-08-03  17:45:20 UTC
   Image Type:   PowerPC Linux Kernel Image (gzip compressed)
   Data Size:    548345 Bytes = 535.5 kB
   Load Address: 00000000
   Entry Point:  00000000
   Verifying Checksum ... OK
   Uncompressing Kernel Image ... OK
 
<hang>
what's the problem?? 
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