yamon无法进入交互模式

[无忧老猪]

sigma开发板smp8654，上电后，启动到yamon时，串口提示如下：
我想进入交互模式，可我按什么键，都进入不了yamon交互模式。

**********************************
* YAMON ROM Monitor
* Revision 02.13-SIGMADESIGNS-24-R2.13-24
**********************************
Memory: code: 0x86000000-0x86060000, 0x85200000-0x85204000
reserved data: 0x86200000-0x86300000, 0x86700000-0x87000000
PCI memory: 0x86300000-0x86700000



Version Mismatch !!Nand Flash version [ S I G M 1.0.3 ] and Nand driver version [ S I G M 1.0.6 ] on CS 0!!

!! No NAND hardware found on CS 1 !!


Environment variable 'start' exists. After 5 seconds
it will be interpreted as a YAMON command and executed.
Press Ctrl-C (or do BREAK) to bypass this.

the real size used in this operation is 10516480
ROMFS found at 0xa7000000, Volume name = MIPSLINUX_XLOAD
a7000040 : Name = ., Type = dir, Size = 00000000, Next = 00000040
a7000060 : Name = .., Type = hard link, Size = 00000000, Next = 00000060
a7000090 : Name = vmlinux_xload.zbf, Type = file, Size = 00a06e94, Next = 00000000
Checking zboot signature.. it's a zboot file, signature OK.
ZBOOT_ATTR_PHY_LOAD OFF
g_load_addr=0xc0000000,g_base_addr=0xc30000b0,count=0x00a06e74
Waiting for XLOAD completion.
XLOAD done. status = 0x6 .. OK.
ZBOOT_ATTR_GZIP ON
Decompressing to 0x84000000 ..
Output length: 0x00c208fb(12716283)
Decompressing decrypted data from 0xa70004c4 to 0x84000000 OK
Linux version 2.6.22.19root@cap9-desktop) (gcc version 4.3.2 (Sourcery G++ Lite 4.3-51) ) #10 PREEMPT Mon Oct 3 23:46:51 CST 2011
Physical map 0xc0000000 to 0x04000000, max remap/kernel size: 0x0c000000/0x18000000.
Configured for SMP865x/867x, detected SMP8655 (revision ES5).
Detected CPU/System/DSP Frequencies: 499.50/333.00/333.00MHz
SMP86xx Enabled Devices under Linux/XENV 0xcfd0bcbc = 0x001b3efc
PCIHost Ethernet Ethernet1 IR FIP I2CM I2CS USB PCIDev1 PCIDev2 PCIDev3 PCIDev4 SATA SCARD SCARD1
CPU revision is: 0001937c
FPU revision is: 01739300

[woshi_ziyu]

Environment variable 'start' exists. After 5 seconds
it will be interpreted as a YAMON command and executed.
Press Ctrl-C (or do BREAK) to bypass this.

[无忧老猪]

Environment variable 'start' exists. After 5 seconds
it will be interpreted as a YAMON command and executed.
Press Ctrl-C (or do BREAK) to bypass this.

就是在这个出现后,我按什么键,都不起作用.Ctrl + C, break,都试过了的.没有任何反应,他继续往下跑.