【场景】
实际用户案例，C3750X stack，从 12.x 升级到 15.x，升级时间 30-45分钟，升级过程中 console 可能出现类似乱码。
升级完成后，再次重启设备，只需要10分钟左右就可以完全启动。
一般情况下，升级IOS15分钟左右就可以完成；客户认为30-45分钟的时长不科学。。。
【原因】
小版本升级（ex. 12.1 to 12.3）只是升级IOS；
大版本升级(ex. 12.x to 15.x)
可能会同时升级IOS+Microcode，所以需要更长时间。
The official explanation for this issue:
With new IOS version you will see microcode getting updated which will take 30-45 minutes when switch booted first time but switch will take normal time to boot afterwards. Actually, The switches have a small MCU(MicroController Unit) to offload processing of some of the hardware interfaces like POE , Fan, power supply etc. (the actual details vary by SKU).
Programming front end microcode should only happen once when upgrading to a higher version with newer microcode.
Just recommend we arrange a 1 hour main window when plan to upgrade 3750X IOS image.推荐的 C3750X升级IOS 操作窗口时间： 不小于1小时。
【升级过程console输出实例】
SW1#reload
Proceed with reload? [confirm]
*Mar 1 00:05:29.227: %SYS-5-RELOAD: Reload requested by console. Reload reason: Reload command
Using driver version 1 for media type 2
Base ethernet MAC Address: 00:07:7d:de:5d:80
Xmodem file system is available.
The password-recovery mechanism is enabled.
Initializing Flash...
mifs[2]: 10 files, 1 directories
mifs[2]: Total bytes : 2097152
mifs[2]: Bytes used : 612352
mifs[2]: Bytes available : 1484800
mifs[2]: mifs fsck took 2 seconds.
mifs[3]: 0 files, 1 directories
mifs[3]: Total bytes : 4194304
mifs[3]: Bytes used : 1024
mifs[3]: Bytes available : 4193280
mifs[3]: mifs fsck took 3 seconds.
mifs[4]: 5 files, 1 directories
mifs[4]: Total bytes : 524288
mifs[4]: Bytes used : 9216
mifs[4]: Bytes available : 515072
mifs[4]: mifs fsck took 1 seconds.
mifs[5]: 5 files, 1 directories
mifs[5]: Total bytes : 524288
mifs[5]: Bytes used : 9216
mifs[5]: Bytes available : 515072
mifs[5]: mifs fsck took 1 seconds.
mifs[6]: 438 files, 8 directories
mifs[6]: Total bytes : 57671680
mifs[6]: Bytes used : 23827968
mifs[6]: Bytes available : 33843712
mifs[6]: mifs fsck took 48 seconds.
...done Initializing Flash.
done.
Loading "c3750e-ipbasek9-mz.150-2.SE9.bin"...c3750e-ipbasek9-mz.150-2.SE9.bin: no such device
Error loading "c3750e-ipbasek9-mz.150-2.SE9.bin"
Interrupt within 5 seconds to abort boot process.
Loading "flash:/c3750e-ipbasek9-mz.150-2.SE9.bin"...@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
File "flash:/c3750e-ipbasek9-mz.150-2.SE9.bin" uncompressed and installed, entry point: 0x3000
executing...
Restricted Rights Legend
Use, duplication, or disclosure by the Government is
subject to restrictions as set forth in subparagraph
(c) of the Commercial Computer Software - Restricted
Rights clause at FAR sec. 52.227-19 and subparagraph
(c) (1) (ii) of the Rights in Technical Data and Computer
Software clause at DFARS sec. 252.227-7013.
cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134-1706
Cisco IOS Software, C3750E Software (C3750E-IPBASEK9-M), Version 15.0(2)SE9, RELEASE SOFTWARE (fc1)
Technical Support:
http://www.cisco.com/techsupportCopyright (c) 1986-2015 by Cisco Systems, Inc.
Compiled Tue 01-Dec-15 06:27 by prod_rel_team
HULC:Collect Entropy thread starting on box...
Initializing flashfs...
Using driver version 3 for media type 1
mifs[4]: 0 files, 1 directories
mifs[4]: Total bytes : 6838272
mifs[4]: Bytes used : 1024
mifs[4]: Bytes available : 6837248
mifs[4]: mifs fsck took 1 seconds.
mifs[4]: Initialization complete.
Using driver version 3 for media type 2
mifs[7]: 10 files, 1 directories
mifs[7]: Total bytes : 2097152
mifs[7]: Bytes used : 612352
mifs[7]: Bytes available : 1484800
mifs[7]: mifs fsck took 0 seconds.
mifs[7]: Initialization complete.
mifs[8]: 0 files, 1 directories
mifs[8]: Total bytes : 4194304
mifs[8]: Bytes used : 1024
mifs[8]: Bytes available : 4193280
mifs[8]: mifs fsck took 0 seconds.
mifs[8]: Initialization complete.
mifs[9]: 5 files, 1 directories
mifs[9]: Total bytes : 524288
mifs[9]: Bytes used : 9216
mifs[9]: Bytes available : 515072
mifs[9]: mifs fsck took 1 seconds.
mifs[9]: Initialization complete.
mifs[10]: 5 files, 1 directories
mifs[10]: Total bytes : 524288
mifs[10]: Bytes used : 9216
mifs[10]: Bytes available : 515072
mifs[10]: mifs fsck took 0 seconds.
mifs[10]: Initialization complete.
mifs[11]: 438 files, 8 directories
mifs[11]: Total bytes : 57671680
mifs[11]: Bytes used : 23827968
mifs[11]: Bytes available : 33843712
mifs[11]: mifs fsck took 1 seconds.
mifs[11]: Initialization complete.
...done Initializing flashfs.
Checking for Bootloader upgrade..
Boot Loader upgrade not required (Stage 2)
FIPS: Flash Key Check : Begin
FIPS: Flash Key Check : End, Not Found, FIPS Mode Not Enabled
POST: CPU MIC register Tests : Begin
POST: CPU MIC register Tests : End, Status Passed
POST: MA BIST : Begin
POST: MA BIST : End, Status Passed
POST: TCAM BIST : Begin
POST: TCAM BIST : End, Status Passed
POST: SF ASIC BIST : Begin
POST: SF ASIC BIST : End, Status Passed
POST: Switch Fabric Memory Tests : Begin
POST: Switch Fabric Memory Tests : End, Status Passed
POST: CPU MIC interface Loopback Tests : Begin
POST: CPU MIC interface Loopback Tests : End, Status Passed
POST: PortASIC RingLoopback Tests : Begin
POST: PortASIC RingLoopback Tests : End, Status Passed
extracting front_end/front_end_ucode_info (309 bytes)
Software version is different so extracting
the whole bundle<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<如果看到这句话，是需要Microcode 升级的，请耐心等待
front_end/ (directory)
extracting front_end/fe_type_4 (78520 bytes)
extracting front_end/fe_type_3 (78520 bytes)
extracting front_end/fe_type_2 (78520 bytes)
extracting front_end/fe_type_5_1 (362114 bytes)
extracting front_end/fe_type_5_2 (25166 bytes)
extracting front_end/fe_type_5_0 (594412 bytes)
extracting front_end/fe_type_5_3 (86370 bytes)
extracting front_end/front_end_ucode_info (309 bytes)
extracting ucode_info (77 bytes)
Front-end Microcode IMG MGR: Installed 4 image(s) in cache:
Front-end Microcode IMG MGR: found microcode images for 4 devices.
Image for front-end 0: flash:/front_end_ucode_cache/ucode.3
Image for front-end 0: flash:/front_end_ucode_cache/ucode.4
Image for front-end 0: flash:/front_end_ucode_cache/ucode.5
Image for front-end 0: flash:/front_end_ucode_cache/ucode.6
Front-end Microcode IMG MGR: Preparing to program device microcode...<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Front-end Microcode IMG MGR: Preparing to program device[0]...594412 bytes.
Front-end Microcode IMG MGR: Programming device 0...rwRrrrrrrwssssssssssssssssssspssssssssssssssssssspssssssssssssssssssspssssssssssssssssssspssss
【结束】
等待30-45分钟，升级完成
show version/ping test 检查设备是否正常，再次重启
