问题及现象：
1、从的uboot经tftp下载linux内核镜像：无法下载。现象如下：
##### Boot for TQ3358 Main Menu #####
##### EmbedSky TFTP download mode #####
[1] Download u-boot.bin to Nand Flash
[2] Download MLO to Nand Flash
[3] Download Linux Kernel (zImage.bin) to Nand Flash
[4] Download LOGO Picture (logo.bin) to Nand Flash
[5] Download UBIFS image (root.bin) to Nand Flash
[6] Download YAFFS image (root.bin) to Nand Flash
[7] Download Program to SDRAM and Run it
[8] Boot the system
[9] Format the Nand Flash
[0] Set the boot parameters
[a] Download User Program
[n] Set TFTP parameters(PC IP,TQ3358 IP,Mask IP...)
[p] Test network (TQ3358 Ping PC's IP)
[r] Reboot u-boot
[t] Test kernel Image (zImage)
[q] Return main Menu
Enter your selection: 3
cpsw Waiting for PHY auto negotiation to complete....... done
link up on port 0, speed 10, half duplex
Using cpsw device
TFTP from server 192.168.0.182; our IP address is 192.168.0.241
Filename 'zImage.bin'.
Load address: 0x81000000
Loading: cpsw Waiting for PHY auto negotiation to complete......... TIMEOUT !
link down on port 0
cpsw Waiting for PHY auto negotiation to complete....... done
link up on port 0, speed 10, half duplex
cpsw Waiting for PHY auto negotiation to complete..... done
T cpsw Waiting for PHY auto negotiation to complete......... TIMEOUT !
link down on port 0
cpsw Waiting for PHY auto negotiation to complete..... done
2、内核启动后，通过主机能ping通开发板
ping 192.168.0.238
PING 192.168.0.238 (192.168.0.238) 56(84) bytes of data.
64 bytes from 192.168.0.238: icmp_req=1 ttl=64 time=997 ms
64 bytes from 192.168.0.238: icmp_req=2 ttl=64 time=0.453 ms
64 bytes from 192.168.0.238: icmp_req=3 ttl=64 time=1.96 ms
64 bytes from 192.168.0.238: icmp_req=4 ttl=64 time=0.555 ms
64 bytes from 192.168.0.238: icmp_req=5 ttl=64 time=0.484 ms，
但是内核不停地打印下面的信息：
Please press Enter to activate this console. [ 18.540420] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 18.730939] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 20.730448] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 20.920974] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 22.920389] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 23.110924] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 25.110416] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 25.300951] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 27.300395] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 27.490931] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 29.490379] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 29.680914] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 31.680409] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 31.870945] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 33.870334] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 34.060871] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 36.060402] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 36.250944] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 38.250364] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 38.440904] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 40.440391] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
[ 40.630926] ti81xx_interrupt 1146: VBUS error workaround (delay coming)
