背景

很多朋友因為了解到樹莓派的強大，所以都很快入手了一個準備把玩，可是通常買回後，發現自己沒有HDMI顯示器，即使有一個顯示器，也通常是VGA介面的，缺個VGA轉HDMI接頭。其實，沒有顯示器也還有辦法可以通過一臺主機(安裝有ssh或串列埠通訊的軟體)的命令列遠端登入到樹莓派，通常有兩種方式：

• 通過網路連線，使用ssh遠端登入(這種方式官網文件裡說的很詳細)
• 通過串列埠遠端登入

我們主要講解通過串列埠登入，因為這方面的資料介紹比較少。實際中又通常有很多人要通過串列埠登入。因為他們更加令人受不了的是，自己居然沒有路由器 -_-#, 即使有，也不會尋找DHCP分配給派的ip地址，也就無法通過puTTY這類軟體遠端登入了。

進入正題

要進行串列埠通訊，首先要有一條USB-TTL轉換線和三根杜邦線，杜邦線用來連線USB串列埠轉換器和樹莓派GPIO的UART針腳（6、8、10號）。連線方式：

首次給樹莓派燒完官方系統後是無法通過串列埠登入的，因為官方預設沒有開啟串列埠用來輸出啟動資訊。

開啟UART串列埠除錯

只需要在燒完官方系統的TF卡上找到config.txt檔案，然後再最後面新增一句：

enable_uart=1

儲存後，首先開啟自己PC端的串列埠通訊軟體（如puTTY），設定串列埠波特率為115200

[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Initializing cgroup subsys cpuacct
[    0.000000] Linux version 4.4.9-v7+ ([email protected]9333) (gcc version 4.9
 
.3 6
[    0.000000] CPU: ARMv7 Processor [410fd034] revision 4 (ARMv7), cr=10c5383d
[    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instructie
[    0.000000] Machine model: Raspberry Pi 3 Model B Rev 1.2
[    0.000000] cma: Reserved 8 MiB at 0x3a800000
[    0.000000] Memory policy: Data cache writealloc
[    0.000000] [bcm2709_smp_init_cpus] enter (9520->f3003010)
[    0.000000] [bcm2709_smp_init_cpus] ncores=4
[    0.000000] PERCPU: Embedded 13 pages/cpu @b9f63000 s22592 r8192 d22464 u5328
[    0.000000] Built 1 zonelists in Zone order, mobility grouping on.  Total pa0
[    0.000000] Kernel command line: 8250.nr_uarts=1 dma.dmachans=0x7f35 bcm2708t
[    0.000000] PID hash table entries: 4096 (order: 2, 16384 bytes)             
[    0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes) 
[    0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes)   
[    0.000000] Memory: 939088K/966656K available (6340K kernel code, 432K rwdat)
[    0.000000] Virtual kernel memory layout:                                    
[    0.000000]     vector  : 0xffff0000 - 0xffff1000   (   4 kB)                
[    0.000000]     fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)                
[    0.000000]     vmalloc : 0xbb800000 - 0xff800000   (1088 MB)                
[    0.000000]     lowmem  : 0x80000000 - 0xbb000000   ( 944 MB)                
[    0.000000]     modules : 0x7f000000 - 0x80000000   (  16 MB)                
[    0.000000]       .text : 0x80008000 - 0x807e5330   (8053 kB)                
[    0.000000]       .init : 0x807e6000 - 0x8085e000   ( 480 kB)                
[    0.000000]       .data : 0x8085e000 - 0x808ca088   ( 433 kB)                
[    0.000000]        .bss : 0x808cd000 - 0x8098c1ac   ( 765 kB)                
[    0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1       
[    0.000000] Hierarchical RCU implementation.                                 
[    0.000000]  Build-time adjustment of leaf fanout to 32.                     
[    0.000000] NR_IRQS:16 nr_irqs:16 16                                         
[    0.000000] Architected cp15 timer(s) running at 19.20MHz (phys).            
[    0.000000] clocksource: arch_sys_counter: mask: 0xffffffffffffff max_cycless
[    0.000010] sched_clock: 56 bits at 19MHz, resolution 52ns, wraps every 4398s
[    0.000027] Switching to timer-based delay loop, resolution 52ns             
[    0.000293] Console: colour dummy device 80x30                               
[    0.001344] console [tty1] enabled                                           
[    0.001398] Calibrating delay loop (skipped), value calculated using timer f)
[    0.001466] pid_max: default: 32768 minimum: 301                             
[    0.001799] Mount-cache hash table entries: 2048 (order: 1, 8192 bytes)      
[    0.001842] Mountpoint-cache hash table entries: 2048 (order: 1, 8192 bytes) 
[    0.002800] Disabling cpuset control group subsystem                         
[    0.002858] Initializing cgroup subsys io                                    
[    0.002909] Initializing cgroup subsys memory                                
[    0.002972] Initializing cgroup subsys devices                               
[    0.003014] Initializing cgroup subsys freezer                               
[    0.003056] Initializing cgroup subsys net_cls                               
[    0.003128] CPU: Testing write buffer coherency: ok                          
[    0.003216] ftrace: allocating 21193 entries in 63 pages                     
[    0.052352] CPU0: update cpu_capacity 1024                                   
[    0.052416] CPU0: thread -1, cpu 0, socket 0, mpidr 80000000                 
[    0.052449] [bcm2709_smp_prepare_cpus] enter                                 
[    0.052598] Setting up static identity map for 0x8240 - 0x8274               
[    0.054273] [bcm2709_boot_secondary] cpu:1 started (0) 17                    
[    0.054600] [bcm2709_secondary_init] enter cpu:1                             
[    0.054643] CPU1: update cpu_capacity 1024                                   
[    0.054649] CPU1: thread -1, cpu 1, socket 0, mpidr 80000001                 
[    0.055024] [bcm2709_boot_secondary] cpu:2 started (0) 16                    
[    0.055285] [bcm2709_secondary_init] enter cpu:2                             
[    0.055306] CPU2: update cpu_capacity 1024                                   
[    0.055312] CPU2: thread -1, cpu 2, socket 0, mpidr 80000002                 
[    0.055669] [bcm2709_boot_secondary] cpu:3 started (0) 17                    
[    0.055851] [bcm2709_secondary_init] enter cpu:3                             
[    0.055871] CPU3: update cpu_capacity 1024                                   
[    0.055877] CPU3: thread -1, cpu 3, socket 0, mpidr 80000003                 
[    0.055936] Brought up 4 CPUs                                                
[    0.056034] SMP: Total of 4 processors activated (153.60 BogoMIPS).          
[    0.056064] CPU: All CPU(s) started in HYP mode.                             
[    0.056089] CPU: Virtualization extensions available.                        
[    0.056728] devtmpfs: initialized                                            
[    0.066460] VFP support v0.3: implementor 41 architecture 3 part 40 variant 4
[    0.066819] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, ms
[    0.067534] pinctrl core: initialized pinctrl subsystem                      
[    0.068084] NET: Registered protocol family 16                               
[    0.073270] DMA: preallocated 4096 KiB pool for atomic coherent allocations  
[    0.080087] bcm2709: Mini UART enabled                                       
[    0.080146] hw-breakpoint: found 5 (+1 reserved) breakpoint and 4 watchpoint.
[    0.080193] hw-breakpoint: maximum watchpoint size is 8 bytes.               
[    0.080370] Serial: AMBA PL011 UART driver                                   
[    0.080523] uart-pl011 3f201000.uart: could not find pctldev for node /soc/ge
[    0.080725] bcm2835-mbox 3f00b880.mailbox: mailbox enabled                   
[    0.143041] bcm2835-dma 3f007000.dma: DMA legacy API manager at f3007000, dm1
[    0.144709] SCSI subsystem initialized                                       
[    0.144902] usbcore: registered new interface driver usbfs                   
[    0.145012] usbcore: registered new interface driver hub                     
[    0.145130] usbcore: registered new device driver usb                        
[    0.151913] raspberrypi-firmware soc:firmware: Attached to firmware from 2013
[    0.179166] clocksource: Switched to clocksource arch_sys_counter            
[    0.224478] FS-Cache: Loaded                                                 
[    0.224798] CacheFiles: Loaded                                               
[    0.236962] NET: Registered protocol family 2                                
[    0.237837] TCP established hash table entries: 8192 (order: 3, 32768 bytes) 
[    0.237975] TCP bind hash table entries: 8192 (order: 4, 65536 bytes)        
[    0.238186] TCP: Hash tables configured (established 8192 bind 8192)         
[    0.238299] UDP hash table entries: 512 (order: 2, 16384 bytes)              
[    0.238367] UDP-Lite hash table entries: 512 (order: 2, 16384 bytes)         
[    0.238628] NET: Registered protocol family 1                                
[    0.238960] RPC: Registered named UNIX socket transport module.              
[    0.238992] RPC: Registered udp transport module.                            
[    0.239020] RPC: Registered tcp transport module.                            
[    0.239048] RPC: Registered tcp NFSv4.1 backchannel transport module.        
[    0.240107] hw perfevents: enabled with armv7_cortex_a7 PMU driver, 7 countee
[    0.241544] futex hash table entries: 1024 (order: 4, 65536 bytes)           
[    0.254738] VFS: Disk quotas dquot_6.6.0                                     
[    0.255058] VFS: Dquot-cache hash table entries: 1024 (order 0, 4096 bytes)  
[    0.257470] FS-Cache: Netfs 'nfs' registered for caching                     
[    0.258365] NFS: Registering the id_resolver key type                        
[    0.258446] Key type id_resolver registered                                  
[    0.258475] Key type id_legacy registered                                    
[    0.260778] Block layer SCSI generic (bsg) driver version 0.4 loaded (major )
[    0.260944] io scheduler noop registered                                     
[    0.260982] io scheduler deadline registered (default)                       
[    0.261062] io scheduler cfq registered                                      
[    0.263572] BCM2708FB: allocated DMA memory fac00000                         
[    0.263619] BCM2708FB: allocated DMA channel 0 @ f3007000                    
[    0.269285] Console: switching to colour frame buffer device 80x30           
[    0.274366] Serial: 8250/16550 driver, 1 ports, IRQ sharing disabled         
[    0.276956] console [ttyS0] disabled                                         
[    0.278606] 3f215040.uart: ttyS0 at MMIO 0x3f215040 (irq = 59, base_baud = 30
[    1.012510] console [ttyS0] enabled                                          
[    1.865544] bcm2835-rng 3f104000.rng: hwrng registered                       
[    1.872649] vc-cma: Videocore CMA driver                                     
[    1.878337] vc-cma: vc_cma_base      = 0x00000000                            
[    1.884802] vc-cma: vc_cma_size      = 0x00000000 (0 MiB)                    
[    1.891910] vc-cma: vc_cma_initial   = 0x00000000 (0 MiB)                    
[    1.899211] vc-mem: phys_addr:0x00000000 mem_base=0x3dc00000 mem_size:0x3f00)
[    1.925286] brd: module loaded                                               
[    1.938451] loop: module loaded                                              
[    1.944029] vchiq: vchiq_init_state: slot_zero = 0xbac80000, is_master = 0   
[    1.954020] Loading iSCSI transport class v2.0-870.                          
[    1.961191] usbcore: registered new interface driver smsc95xx                
[    1.968619] dwc_otg: version 3.00a 10-AUG-2012 (platform bus)                
[    2.176252] Core Release: 2.80a                                              
[    2.180978] Setting default values for core params                           
[    2.187409] Finished setting default values for core params                  
[    2.395014] Using Buffer DMA mode                                            
[    2.399954] Periodic Transfer Interrupt Enhancement - disabled               
[    2.407498] Multiprocessor Interrupt Enhancement - disabled                  
[    2.414785] OTG VER PARAM: 0, OTG VER FLAG: 0                                
[    2.420818] Dedicated Tx FIFOs mode                                          
[    2.426212] WARN::dwc_otg_hcd_init:1047: FIQ DMA bounce buffers: virt = 0xba4
[    2.439377] FIQ FSM acceleration enabled for :                               
[    2.439377] Non-periodic Split Transactions                                  
[    2.439377] Periodic Split Transactions                                      
[    2.439377] High-Speed Isochronous Endpoints                                 
[    2.439377] Interrupt/Control Split Transaction hack enabled                 
[    2.469909] WARN::hcd_init_fiq:413: FIQ on core 1 at 0x804459c4              
[    2.477566] WARN::hcd_init_fiq:414: FIQ ASM at 0x80445d34 length 36          
[    2.485546] WARN::hcd_init_fiq:439: MPHI regs_base at 0xbb932000             
[    2.493272] dwc_otg 3f980000.usb: DWC OTG Controller                         
[    2.499937] dwc_otg 3f980000.usb: new USB bus registered, assigned bus numbe1
[    2.510586] dwc_otg 3f980000.usb: irq 62, io mem 0x00000000                  
[    2.517903] Init: Port Power? op_state=1                                     
[    2.523494] Init: Power Port (0)                                             
[    2.528515] usb usb1: New USB device found, idVendor=1d6b, idProduct=0002    
[    2.537043] usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber1
[    2.547560] usb usb1: Product: DWC OTG Controller                            
[    2.553963] usb usb1: Manufacturer: Linux 4.4.9-v7+ dwc_otg_hcd              
[    2.561609] usb usb1: SerialNumber: 3f980000.usb                             
[    2.568657] hub 1-0:1.0: USB hub found                                       
[    2.574085] hub 1-0:1.0: 1 port detected                                     
[    2.580519] usbcore: registered new interface driver usb-storage             
[    2.588417] mousedev: PS/2 mouse device common for all mice                  
[    2.596331] bcm2835-cpufreq: min=600000 max=1200000                          
[    2.603109] sdhci: Secure Digital Host Controller Interface driver           
[    2.610979] sdhci: Copyright(c) Pierre Ossman                                
[    2.617277] sdhost: log_buf @ bac13000 (fac13000)                            
[    2.699193] mmc0: sdhost-bcm2835 loaded - DMA enabled (>1)                   
[    2.708607] mmc-bcm2835 3f300000.mmc: mmc_debug:0 mmc_debug2:0               
[    2.716152] mmc-bcm2835 3f300000.mmc: DMA channel allocated                  
[    2.756235] mmc0: host does not support reading read-only switch, assuming we
[    2.759278] sdhci-pltfm: SDHCI platform and OF driver helper                 
[    2.759675] ledtrig-cpu: registered to indicate activity on CPUs             
[    2.759788] hidraw: raw HID events driver (C) Jiri Kosina                    
[    2.759981] usbcore: registered new interface driver usbhid                  
[    2.759983] usbhid: USB HID core driver                                      
[    2.760535] Initializing XFRM netlink socket                                 
[    2.760558] NET: Registered protocol family 17                               
[    2.760674] Key type dns_resolver registered                                 
[    2.761168] Registering SWP/SWPB emulation handler                           
[    2.761941] registered taskstats version 1                                   
[    2.762136] vc-sm: Videocore shared memory driver                            
[    2.762145] [vc_sm_connected_init]: start                                    
[    2.767935] [vc_sm_connected_init]: end - returning 0                        
[    2.769323] 3f201000.uart: ttyAMA0 at MMIO 0x3f201000 (irq = 87, base_baud =2
[    2.769695] of_cfs_init                                                      
[    2.769770] of_cfs_init: OK                                                  
[    2.779276] Indeed it is in host mode hprt0 = 00021501                       
[    2.878496] Waiting for root device /dev/mmcblk0p2...                        
[    2.880327] mmc0: new high speed SDHC card at address 0007                   
[    2.880931] mmcblk0: mmc0:0007 SD32G 29.0 GiB                                
[    2.890352]  mmcblk0: p1 p2                                                  
[    2.905435] EXT4-fs (mmcblk0p2): INFO: recovery required on readonly filesysm
[    2.909269] mmc1: queuing unknown CIS tuple 0x80 (2 bytes)                   
[    2.910816] mmc1: queuing unknown CIS tuple 0x80 (3 bytes)                   
[    2.912361] mmc1: queuing unknown CIS tuple 0x80 (3 bytes)                   
[    2.915156] mmc1: queuing unknown CIS tuple 0x80 (7 bytes)                   
[    2.943856] EXT4-fs (mmcblk0p2): write access will be enabled during recovery
[    2.959202] usb 1-1: new high-speed USB device number 2 using dwc_otg        
[    2.967349] Indeed it is in host mode hprt0 = 00001101                       
[    2.975113] EXT4-fs (mmcblk0p2): recovery complete                           
[    3.008351] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. )
[    3.019558] VFS: Mounted root (ext4 filesystem) readonly on device 179:2.    
[    3.029005] devtmpfs: mounted                                                
[    3.034767] Freeing unused kernel memory: 480K (807e6000 - 8085e000)         
[    3.045289] mmc1: new high speed SDIO card at address 0001                   
[    3.169469] usb 1-1: New USB device found, idVendor=0424, idProduct=9514     
[    3.177952] usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[    3.187663] hub 1-1:1.0: USB hub found                                       
[    3.193275] hub 1-1:1.0: 5 ports detected                                    
[    3.311752] random: systemd urandom read with 55 bits of entropy available   
[    3.324555] systemd[1]: systemd 215 running in system mode. (+PAM +AUDIT +SE)
[    3.341939] systemd[1]: Detected architecture 'arm'.                         
[    3.479253] usb 1-1.1: new high-speed USB device number 3 using dwc_otg      
[    3.479431] NET: Registered protocol family 10                               
[    3.480778] systemd[1]: Inserted module 'ipv6'                               
[    3.484035] systemd[1]: Set hostname to <raspberrypi>.                       
[    3.619538] usb 1-1.1: New USB device found, idVendor=0424, idProduct=ec00   
[    3.628441] usb 1-1.1: New USB device strings: Mfr=0, Product=0, SerialNumbe0
[    3.642514] smsc95xx v1.0.4                                                  
[    3.713078] smsc95xx 1-1.1:1.0 eth0: register 'smsc95xx' at usb-3f980000.usbf
[    3.819225] usb 1-1.5: new full-speed USB device number 4 using dwc_otg      
[    3.937391] systemd[1]: Expecting device dev-ttyS0.device...                 
[    3.947641] systemd[1]: Starting Forward Password Requests to Wall Directory.
[    3.959468] systemd[1]: Started Forward Password Requests to Wall Directory .
[    3.971020] systemd[1]: Starting Remote File Systems (Pre).                  
[    3.981043] systemd[1]: Reached target Remote File Systems (Pre).            
[    3.989317] systemd[1]: Starting Encrypted Volumes.                          
[    3.998473] systemd[1]: Reached target Encrypted Volumes.                    
[    4.006104] systemd[1]: Starting Arbitrary Executable File Formats File Syst.
[    4.021712] systemd[1]: Set up automount Arbitrary Executable File Formats F.
[    4.035350] usb 1-1.5: New USB device found, idVendor=248a, idProduct=8566   
[    4.035407] systemd[1]: Starting Swap.                                       
[    4.050304] usb 1-1.5: New USB device strings: Mfr=1, Product=2, SerialNumbe0
[    4.050314] usb 1-1.5: Product: Wireless Receiver                            
[    4.050320] usb 1-1.5: Manufacturer: Telink                                  
[    4.077599] systemd[1]: Reached target Swap.                                 
[    4.084071] systemd[1]: Expecting device dev-mmcblk0p1.device...             
[    4.094640] systemd[1]: Starting Root Slice.                                 
[    4.103335] systemd[1]: Created slice Root Slice.                            
[    4.110175] systemd[1]: Starting User and Session Slice.                     
[    4.110607] input: Telink Wireless Receiver as /devices/platform/soc/3f980000
[    4.136483] systemd[1]: Created slice User and Session Slice.                
[    4.144354] systemd[1]: Starting /dev/initctl Compatibility Named Pipe.      
[    4.155413] systemd[1]: Listening on /dev/initctl Compatibility Named Pipe.  
[    4.164518] systemd[1]: Starting Delayed Shutdown Socket.                    
[    4.172018] hid-generic 0003:248A:8566.0001: input,hidraw0: USB HID v1.11 Ke0
[    4.190913] systemd[1]: Listening on Delayed Shutdown Socket.                
[    4.198668] systemd[1]: Starting Journal Socket (/dev/log).                  
[    4.208574] systemd[1]: Listening on Journal Socket (/dev/log).              
[    4.216559] systemd[1]: Starting udev Control Socket.                        
[    4.225900] systemd[1]: Listening on udev Control Socket.                    
[    4.233386] systemd[1]: Starting udev Kernel Socket.                         
[    4.242559] systemd[1]: Listening on udev Kernel Socket.                     
[    4.249979] systemd[1]: Starting Journal Socket.                             
[    4.258856] systemd[1]: Listening on Journal Socket.                         
[    4.265988] systemd[1]: Starting System Slice.                               
[    4.274775] systemd[1]: Created slice System Slice.                          
[    4.277133] input: Telink Wireless Receiver as /devices/platform/soc/3f980001
[    4.298107] systemd[1]: Starting File System Check on Root Device...         
[    4.329662] hid-generic 0003:248A:8566.0002: input,hidraw1: USB HID v1.11 Mo1
[    4.359781] systemd[1]: Starting system-systemd\x2dfsck.slice.               
[    4.370389] systemd[1]: Created slice system-systemd\x2dfsck.slice.          
[    4.378809] systemd[1]: Starting system-autologin.slice.                     
[    4.389362] systemd[1]: Created slice system-autologin.slice.                
[    4.397243] systemd[1]: Starting system-serial\x2dgetty.slice.               
[    4.407784] systemd[1]: Created slice system-serial\x2dgetty.slice.          
[    4.416334] systemd[1]: Starting Increase datagram queue length...           
[    4.429429] systemd[1]: Starting Restore / save the current clock...         
[    4.471153] systemd[1]: Starting Load Kernel Modules...                      
[    4.483448] systemd[1]: Starting udev Coldplug all Devices...                
[    4.497008] systemd[1]: Mounted Huge Pages File System.                      
[    4.505295] systemd[1]: Starting Create list of required static device nodes.
[    4.572731] systemd[1]: Started Set Up Additional Binary Formats.            
[    4.581676] systemd[1]: Mounting POSIX Message Queue File System...          
[    4.621927] fuse init (API version 7.23)                                     
[    4.660016] systemd[1]: Mounting Debug File System...                        
[    4.670488] i2c /dev entries driver                                          
[    4.672420] systemd[1]: Starting Slices.                                     
[    4.684393] systemd[1]: Reached target Slices.                               
[    4.697543] systemd[1]: Started Increase datagram queue length.              
[    4.724812] systemd[1]: Started Restore / save the current clock.            
[    4.736083] systemd[1]: Started Load Kernel Modules.                         
[    4.783579] systemd[1]: Started Create list of required static device nodes .
[    4.799779] systemd[1]: Mounted POSIX Message Queue File System.             
[    4.810645] systemd[1]: Mounted Debug File System.                           
[    4.821645] systemd[1]: Time has been changed                                
[    4.831061] systemd[1]: Started udev Coldplug all Devices.                   
[    4.962840] systemd[1]: Starting Create Static Device Nodes in /dev...       
[    5.009803] systemd[1]: Starting Apply Kernel Variables...                   
[    5.021963] systemd[1]: Mounting FUSE Control File System...                 
[    5.034783] systemd[1]: Mounting Configuration File System...                
[    5.047794] systemd[1]: Starting Syslog Socket.                              
[    5.057180] systemd[1]: Listening on Syslog Socket.                          
[    5.064278] systemd[1]: Starting Journal Service...                          
[    5.078057] systemd[1]: Started Journal Service.                             

Raspbian GNU/Linux 8 raspberrypi ttyS0                                          

raspberrypi login: 

大功告成