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O365

Capacitor Parallel/Series (電容串並聯)

一個基本的電容 (忽略所有邊緣效應下), 相當於兩塊板子, 中間夾著一塊絕緣體. 其電容值與兩塊板子的面積成正比, 與絕緣材料的厚度成反比

面積越大, 容值越大 絕緣越厚, 容值越小

當兩個電容並聯(Parallel), 相當於得到更大的面積, 因此電容值就會上升;

    +--|(--+
----+      +---
    +--|(--+

    等效大面積電容

    |(
----|(---
    |(

而兩個電容串聯(Series), 相當於得到一塊更厚的絕緣材料, 因此電容值就會下降.

----|(---|(----

    等效厚絕緣

----|     (---

總結比較

特性 Parallel Series
總容量 增加 C_all = C_1 + C_2 + ... + C_n 減少 1/C_all = 1/C_1 + 1/C_2 + ... + 1/C_n
耐壓值 等於最低的那個電容 增加 (各電容耐壓之和)
電壓 (ideally) V_all = V_1 = V_2 = V_n V_all = V_1 + V_2 + ... + V_n
電荷量 Q_all = Q_1 + Q_2 + ... + Q_n Q_all = Q_1 = Q_2 = Q_n
常見用途 增加濾波容量、降低ESR 提高耐壓、調整電容值

ps. ESR (等效串聯內阻), 因現實中電容並非理想的條件, 因此電容的等效為 電容內串聯一個電阻, 此電阻稱為 ESR

Reference

Kernel NFS

  • Create tap0 device on Hos-OS

    $ sudo ip tuntap add dev tap0 mode tap
$ sudo ip link set dev tap0 up
$ sudo ip address add dev tap0 192.168.1.1/16   # set tap ip-address
$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 000
    link/ether 08:00:27:12:4d:ae brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global dynamic noprefixroute enp0s3
       valid_lft 69272sec preferred_lft 69272sec
    inet6 fd17:625c:f037:2:2eb4:5406:23c4:5c74/64 scope global temporary dynamic
       valid_lft 86001sec preferred_lft 14001sec
    inet6 fd17:625c:f037:2:18ae:2c0b:75e6:7fc3/64 scope global dynamic mngtmpaddr noprefixroute
       valid_lft 86001sec preferred_lft 14001sec
    inet6 fe80::9709:3d8d:24ac:28e2/64 scope link noprefixroute
       valid_lft forever preferred_lft forever
3: enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 000
    link/ether 08:00:27:30:c4:a9 brd ff:ff:ff:ff:ff:ff
    inet 192.168.56.101/24 brd 192.168.56.255 scope global dynamic noprefixroute enp0s8
       valid_lft 571sec preferred_lft 571sec
    inet6 fe80::7220:5560:ed27:bec8/64 scope link noprefixroute
       valid_lft forever preferred_lft forever
4: tap0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qle 1000
    link/ether f6:5e:c5:fe:1a:4a brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.1/16 scope global tap0
       valid_lft forever preferred_lft forever

  • Kernel configuration

    > Device Drivers > Remoteproc drivers
    <*> Support for Remote Processor subsystem
> Device Drivers > Rpmsg drivers
    <*> RPMSG device interface
    <*> Virtio RPMSG bus driver

    > Device Drivers > Network device support
    --- Network device support
    [*]   Network core driver support
    < >     Bonding driver support
    < >     Dummy net driver support
    < >     EQL (serial line load balancing) support
    < >     Ethernet team driver support  ----
    < >     MAC-VLAN support
    < >     Virtual eXtensible Local Area Network (VXLAN)
    < >     Generic Network Virtualization Encapsulation
    < >     GPRS Tunneling Protocol datapath (GTP-U)
    < >     IEEE 802.1AE MAC-level encryption (MACsec)
    < >     Network console logging support
    <*>     Universal TUN/TAP device driver support

> Device Drivers > Network device support > Ethernet driver support
    [*]   SMC (SMSC)/Western Digital devices
    <*>     SMC 91C9x/91C1xxx support
    < >     SMSC LAN911[5678] support
    <*>     SMSC LAN911x/LAN921x families embedded ethernet support

    > File systems > Network File Systems
    --- Network File Systems
    <*>   NFS client support
    <*>     NFS client support for NFS version 2
    <*>     NFS client support for NFS version 3
    [ ]       NFS client support for the NFSv3 ACL protocol extension
    <*>     NFS client support for NFS version 4
    [*]     Provide swap over NFS support
    [*]   NFS client support for NFSv4.1
    [*]     NFS client support for NFSv4.2
    (kernel.org) NFSv4.1 Implementation ID Domain
    [*]     NFSv4.1 client support for migration
    [*]   Root file system on NFS
    [ ]   Use the legacy NFS DNS resolver

    > Kernel hacking > Compile-time checks and compiler options
    [*] Compile the kernel with debug info
    [ ]   Reduce debugging information
    [ ]   Produce split debuginfo in .dwo files
    [*]   Generate dwarf4 debuginfo
    [*]   Provide GDB scripts for kernel debugging
    [*] Enable __must_check logic
    (1024) Warn for stack frames larger than (needs gcc 4.4)
    [ ] Strip assembler-generated symbols during link
    [*] Generate readable assembler code
    [ ] Enable unused/obsolete exported symbols

  • Qemu start on Host-OS

    $ qemu-system-arm -M vexpress-a9 \
   -smp 2 \
   -m 128M \
   -kernel arch/arm/boot/zImage \
   -append "rdinit=/linuxrc console=ttyAMA0 loglevel=8" \
   -dtb arch/arm/boot/dts/vexpress-v2p-ca9.dtb \
   -initrd initramfs.cpio.gz \
   -net nic -net tap,ifname=tap0,script=no,downscript=no \
   -nographic

  • Network status of Guest-OS

    / # ifconfig
eth0      Link encap:Ethernet  HWaddr 52:54:00:12:34:56
          inet addr:192.168.1.3  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:22

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

/ # ping 192.168.1.1
    PING 192.168.1.1 (192.168.1.1): 56 data bytes
    64 bytes from 192.168.1.1: seq=0 ttl=64 time=71.960 ms
    64 bytes from 192.168.1.1: seq=1 ttl=64 time=1.855 ms
    64 bytes from 192.168.1.1: seq=2 ttl=64 time=1.152 ms
    ...
/ #

  • Mount NFS on Guest-OS

    / # mount -t nfs -o nolock 192.168.1.1:/home/nfs /mnt/rwfs

  • kernel boot log

    use ethernet driver smsc911x

    ...
smsc911x 4e000000.ethernet eth0: SMSC911x/921x identified at 0x8c910000, IRQ: 22

    Booting Linux on physical CPU 0x0
Linux version 4.19.319 (lub20wl@lub20wl-virtualbox) (gcc version 7.5.0 (Linaro GCC 7.5-2019.12)) 7 SMP Sun Jan 25 11:20:51 CST 2026
CPU: ARMv7 Processor [410fc090] revision 0 (ARMv7), cr=10c5387d
CPU: PIPT / VIPT nonaliasing data cache, VIPT nonaliasing instruction cache
OF: fdt: Machine model: V2P-CA9
Memory policy: Data cache writealloc
On node 0 totalpages: 32768
  Normal zone: 256 pages used for memmap
  Normal zone: 0 pages reserved
  Normal zone: 32768 pages, LIFO batch:7
percpu: Embedded 16 pages/cpu s32908 r8192 d24436 u65536
pcpu-alloc: s32908 r8192 d24436 u65536 alloc=16*4096
pcpu-alloc: [0] 0 [0] 1 [0] 2 [0] 3
Built 1 zonelists, mobility grouping on.  Total pages: 32512
Kernel command line: rdinit=/linuxrc console=ttyAMA0 loglevel=8
log_buf_len individual max cpu contribution: 4096 bytes
log_buf_len total cpu_extra contributions: 12288 bytes
log_buf_len min size: 16384 bytes
log_buf_len: 32768 bytes
early log buf free: 15164(92%)
Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
Memory: 114504K/131072K available (6144K kernel code, 473K rwdata, 1292K rodata, 1024K init, 146Kbss, 16568K reserved, 0K cma-reserved)
Virtual kernel memory layout:
    vector  : 0xffff0000 - 0xffff1000   (   4 kB)
    fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)
    vmalloc : 0x88800000 - 0xff800000   (1904 MB)
    lowmem  : 0x80000000 - 0x88000000   ( 128 MB)
    modules : 0x7f000000 - 0x80000000   (  16 MB)
      .text : 0x(ptrval) - 0x(ptrval)   (7136 kB)
      .init : 0x(ptrval) - 0x(ptrval)   (1024 kB)
      .data : 0x(ptrval) - 0x(ptrval)   ( 474 kB)
       .bss : 0x(ptrval) - 0x(ptrval)   ( 147 kB)
SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
rcu: Hierarchical RCU implementation.
rcu:    RCU event tracing is enabled.
rcu:    RCU restricting CPUs from NR_CPUS=8 to nr_cpu_ids=4.
rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=4
NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16
L2C: platform modifies aux control register: 0x02020000 -> 0x02420000
L2C: DT/platform modifies aux control register: 0x02020000 -> 0x02420000
L2C-310 enabling early BRESP for Cortex-A9
L2C-310 full line of zeros enabled for Cortex-A9
L2C-310 dynamic clock gating disabled, standby mode disabled
L2C-310 cache controller enabled, 8 ways, 128 kB
L2C-310: CACHE_ID 0x410000c8, AUX_CTRL 0x46420001
sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 89478484971ns
clocksource: arm,sp804: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275 ns
smp_twd: clock not found -2
Console: colour dummy device 80x30
Calibrating local timer... 103.46MHz.
Calibrating delay loop... 652.08 BogoMIPS (lpj=3260416)
CPU: Testing write buffer coherency: ok
CPU0: Spectre v2: using BPIALL workaround
pid_max: default: 32768 minimum: 301
Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
Setting up static identity map for 0x60100000 - 0x60100060
rcu: Hierarchical SRCU implementation.
smp: Bringing up secondary CPUs ...
CPU1: thread -1, cpu 1, socket 0, mpidr 80000001
CPU1: Spectre v2: using BPIALL workaround
CPU2: failed to boot: -38
CPU3: failed to boot: -38
smp: Brought up 1 node, 2 CPUs
SMP: Total of 2 processors activated (1337.75 BogoMIPS).
CPU: All CPU(s) started in SVC mode.
devtmpfs: initialized
clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
futex hash table entries: 1024 (order: 4, 65536 bytes)
NET: Registered protocol family 16
DMA: preallocated 256 KiB pool for atomic coherent allocations
cpuidle: using governor ladder
hw-breakpoint: debug architecture 0x4 unsupported.
Serial: AMBA PL011 UART driver
10009000.uart: ttyAMA0 at MMIO 0x10009000 (irq = 29, base_baud = 0) is a PL011 rev1
console [ttyAMA0] enabled
1000a000.uart: ttyAMA1 at MMIO 0x1000a000 (irq = 30, base_baud = 0) is a PL011 rev1
1000b000.uart: ttyAMA2 at MMIO 0x1000b000 (irq = 31, base_baud = 0) is a PL011 rev1
1000c000.uart: ttyAMA3 at MMIO 0x1000c000 (irq = 32, base_baud = 0) is a PL011 rev1
OF: amba_device_add() failed (-19) for /smb@4000000/motherboard/iofpga@7,00000000/wdt@f000
OF: amba_device_add() failed (-19) for /memory-controller@100e0000
OF: amba_device_add() failed (-19) for /memory-controller@100e1000
OF: amba_device_add() failed (-19) for /watchdog@100e5000
irq: type mismatch, failed to map hwirq-75 for interrupt-controller@1e001000!
SCSI subsystem initialized
usbcore: registered new interface driver usbfs
usbcore: registered new interface driver hub
usbcore: registered new device driver usb
clocksource: Switched to clocksource arm,sp804
NET: Registered protocol family 2
IP idents hash table entries: 2048 (order: 2, 16384 bytes)
tcp_listen_portaddr_hash hash table entries: 512 (order: 0, 6144 bytes)
TCP established hash table entries: 1024 (order: 0, 4096 bytes)
TCP bind hash table entries: 1024 (order: 1, 8192 bytes)
TCP: Hash tables configured (established 1024 bind 1024)
UDP hash table entries: 256 (order: 1, 8192 bytes)
UDP-Lite hash table entries: 256 (order: 1, 8192 bytes)
NET: Registered protocol family 1
RPC: Registered named UNIX socket transport module.
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
RPC: Registered tcp NFSv4.1 backchannel transport module.
Unpacking initramfs...
Freeing initrd memory: 5196K
hw perfevents: enabled with armv7_cortex_a9 PMU driver, 7 counters available
workingset: timestamp_bits=30 max_order=15 bucket_order=0
squashfs: version 4.0 (2009/01/31) Phillip Lougher
NFS: Registering the id_resolver key type
Key type id_resolver registered
Key type id_legacy registered
nfs4filelayout_init: NFSv4 File Layout Driver Registering...
nfs4flexfilelayout_init: NFSv4 Flexfile Layout Driver Registering...
jffs2: version 2.2. (NAND) © 2001-2006 Red Hat, Inc.
9p: Installing v9fs 9p2000 file system support
io scheduler noop registered (default)
io scheduler mq-deadline registered
io scheduler kyber registered
40000000.flash: Found 2 x16 devices at 0x0 in 32-bit bank. Manufacturer ID 0x000000 Chip ID 0x00000
Intel/Sharp Extended Query Table at 0x0031
Using buffer write method
erase region 0: offset=0x0,size=0x40000,blocks=256
40000000.flash: Found 2 x16 devices at 0x0 in 32-bit bank. Manufacturer ID 0x000000 Chip ID 0x00000
Intel/Sharp Extended Query Table at 0x0031
Using buffer write method
erase region 0: offset=0x0,size=0x40000,blocks=256
Concatenating MTD devices:
(0): "40000000.flash"
(1): "40000000.flash"
into device "40000000.flash"
tun: Universal TUN/TAP device driver, 1.6
smsc911x 4e000000.ethernet: Linked as a consumer to regulator.1
smsc911x 4e000000.ethernet eth0: MAC Address: 52:54:00:12:34:56
usbcore: registered new interface driver usbhid
usbhid: USB HID core driver
oprofile: using arm/armv7-ca9
NET: Registered protocol family 17
9pnet: Installing 9P2000 support
Key type dns_resolver registered
Registering SWP/SWPB emulation handler
input: AT Raw Set 2 keyboard as /devices/platform/smb@4000000/smb@4000000:motherboard/smb@4000000motherboard:iofpga@7,00000000/10006000.kmi/serio0/input/input0
Freeing unused kernel memory: 1024K
Run /linuxrc as init process
Starting /etc/rc.d/init.d/S01filesystems
Mounting filesystems
Starting /etc/rc.d/init.d/S02network
Network up
Generic PHY 4e000000.ethernet-ffffffff:01: attached PHY driver [Generic PHY] (mii_bus:phy_addr=4e00000.ethernet-ffffffff:01, irq=POLL)
smsc911x 4e000000.ethernet eth0: SMSC911x/921x identified at 0x8c910000, IRQ: 22
Starting /etc/rc.d/init.d/S03hostname

Please press Enter to activate this console.
/ #