구차니의 잡동사니 모음

Timer-based delays

In 2012, ARM contributed a new udelay implementation allowing the system timer built into many ARMv7 CPUs to be used instead of a busy-wait loop.[8] Timer based delays are more robust on systems that use frequency scaling to dynamically adjust the processor's speed at runtime, as loops_per_jiffies values may not necessarily scale linearly. Also, since the timer frequency is known in advance, no calibration is needed at boot time.

One side effect of this change is that the BogoMIPS value will reflect the timer frequency, not the CPU's core frequency. Typically the timer frequency is much lower than the processor's maximum frequency, and some users may be surprised to see an unusually low BogoMIPS value when comparing against systems that use traditional busy-wait loops.

[링크 : http://en.wikipedia.org/wiki/BogoMips] 

ARM: 7452/1: delay: allow timer-based delay implementation to be selected

This patch allows a timer-based delay implementation to be selected by

switching the delay routines over to use get_cycles, which is

implemented in terms of read_current_timer. This further allows us to

skip the loop calibration and have a consistent delay function in the

face of core frequency scaling.

To avoid the pain of dealing with memory-mapped counters, this

implementation uses the co-processor interface to the architected timers

when they are available. The previous loop-based implementation is

kept around for CPUs without the architected timers and we retain both

the maximum delay (2ms) and the corresponding conversion factors for

determining the number of loops required for a given interval. Since the

indirection of the timer routines will only work when called from C,

the sa1100 sleep routines are modified to branch to the loop-based delay

functions directly.

[링크 : https://git.kernel.org/.../linux.git/commit/?id=d0a533b18235d36206b9b422efadb7cee444dfdb] 

$ dmesg

[ 9052.747682] usb 1-1.2: USB disconnect, device number 9

[ 9052.748051] MOSCHIP usb-ethernet driver 1-1.2:1.0 eth1: unregister 'MOSCHIP usb-ethernet driver' usb-bcm2708_usb-1.2, MOSCHIP 7830/7832/7730 usb-NET adapter

[ 9054.028020] usb 1-1.4: USB disconnect, device number 8

[ 9096.507202] usb 1-1.4: new high-speed USB device number 10 using dwc_otg

[ 9096.760443] usb 1-1.4: New USB device found, idVendor=148f, idProduct=2573

[ 9096.760468] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0

[ 9096.760485] usb 1-1.4: Product: 802.11 bg WLAN

[ 9096.760502] usb 1-1.4: Manufacturer: Ralink

[ 9096.887401] usb 1-1.4: reset high-speed USB device number 10 using dwc_otg

[ 9097.331348] ieee80211 phy2: rt2x00_set_chip: Info - Chipset detected - rt: 2573, rf: 0002, rev: 000a

[ 9097.332541] ieee80211 phy2: Selected rate control algorithm 'minstrel_ht'

[ 9097.335102] usbcore: registered new interface driver rt73usb

[ 9097.433128] ieee80211 phy2: rt2x00lib_request_firmware: Info - Loading firmware file 'rt73.bin'

[ 9097.434590] ieee80211 phy2: rt2x00lib_request_firmware: Info - Firmware detected - version: 1.7

uio                     8119  1 uio_pdrv_genirq 

$ dmesg

[ 7446.882346] usb 1-1.2: new high-speed USB device number 6 using dwc_otg

[ 7446.998227] usb 1-1.2: New USB device found, idVendor=0411, idProduct=01a2

[ 7446.998251] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3

[ 7446.998269] usb 1-1.2: Product: 802.11 n WLAN

[ 7446.998285] usb 1-1.2: Manufacturer: Ralink

[ 7446.998301] usb 1-1.2: SerialNumber: 1.0

[ 7447.106556] cfg80211: Calling CRDA to update world regulatory domain

[ 7447.272356] usb 1-1.2: reset high-speed USB device number 6 using dwc_otg

[ 7447.381554] ieee80211 phy0: rt2x00_set_rt: Info - RT chipset 3070, rev 0201 detected

[ 7447.413690] ieee80211 phy0: rt2x00_set_rf: Info - RF chipset 0005 detected

[ 7447.436162] ieee80211 phy0: Selected rate control algorithm 'minstrel_ht'

[ 7447.438442] usbcore: registered new interface driver rt2800usb

[ 7447.505538] ieee80211 phy0: rt2x00lib_request_firmware: Info - Loading firmware file 'rt2870.bin'

[ 7447.516358] ieee80211 phy0: rt2x00lib_request_firmware: Info - Firmware detected - version: 0.29

$ lsusb -t

/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dwc_otg/1p, 480M

    |__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/5p, 480M

        |__ Port 1: Dev 3, If 0, Class=vend., Driver=smsc95xx, 480M

        |__ Port 2: Dev 6, If 0, Class=vend., Driver=rt2800usb, 480M

        |__ Port 5: Dev 5, If 0, Class=HID, Driver=usbhid, 1.5M

$ lsmod

Module                  Size  Used by

arc4                    1745  2

rt2800usb              17898  0

rt2800lib              71839  1 rt2800usb

rt2x00usb               8764  1 rt2800usb

rt2x00lib              37292  3 rt2x00usb,rt2800lib,rt2800usb

mac80211              483934  3 rt2x00lib,rt2x00usb,rt2800lib

cfg80211              395318  2 mac80211,rt2x00lib

crc_ccitt               1153  1 rt2800lib

rfkill                 16651  2 cfg80211

snd_bcm2835            18850  0

snd_pcm                75388  1 snd_bcm2835

snd_seq                53078  0

snd_seq_device          5628  1 snd_seq

snd_timer              17784  2 snd_pcm,snd_seq

snd                    51667  5 snd_bcm2835,snd_timer,snd_pcm,snd_seq,snd_seq_device

joydev                  8903  0

evdev                   9950  1

uio_pdrv_genirq         2958  0

uio                     8119  1 uio_pdrv_genirq

$ dmesg

[ 8474.601826] usb 1-1.4: new high-speed USB device number 7 using dwc_otg

[ 8474.706348] usb 1-1.4: New USB device found, idVendor=9710, idProduct=7830

[ 8474.706373] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3

[ 8474.706391] usb 1-1.4: Product: USB-MAC Controller

[ 8474.706408] usb 1-1.4: Manufacturer: Moschip Semiconductor

[ 8474.706424] usb 1-1.4: SerialNumber: 00001809

[ 8474.779485] usb 1-1.4: applying rev.C fixup

[ 8474.791907] usb 1-1.4: applying rev.C fixup

[ 8474.813989] MOSCHIP usb-ethernet driver 1-1.4:1.0 eth1: register 'MOSCHIP usb-ethernet driver' at usb-bcm2708_usb-1.4, MOSCHIP 7830/7832/7730 usb-NET adapter, 00:00:00:00:18:09

[ 8474.814649] usbcore: registered new interface driver MOSCHIP usb-ethernet driver

[ 8477.695159] usb 1-1.2: USB disconnect, device number 6

$ lsusb -t

/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dwc_otg/1p, 480M

    |__ Port 1: Dev 2, If 0, Class=hub, Driver=hub/5p, 480M

        |__ Port 1: Dev 3, If 0, Class=vend., Driver=smsc95xx, 480M

        |__ Port 4: Dev 7, If 0, Class=vend., Driver=MOSCHIP usb-ethernet driver, 480M

        |__ Port 5: Dev 5, If 0, Class=HID, Driver=usbhid, 1.5M

$ lsmod

Module                  Size  Used by

mcs7830                 5295  0

arc4                    1745  0

rt2800usb              17898  0

rt2800lib              71839  1 rt2800usb

rt2x00usb               8764  1 rt2800usb

rt2x00lib              37292  3 rt2x00usb,rt2800lib,rt2800usb

mac80211              483934  3 rt2x00lib,rt2x00usb,rt2800lib

cfg80211              395318  2 mac80211,rt2x00lib

crc_ccitt               1153  1 rt2800lib

rfkill                 16651  1 cfg80211

snd_bcm2835            18850  0

snd_pcm                75388  1 snd_bcm2835

snd_seq                53078  0

snd_seq_device          5628  1 snd_seq

snd_timer              17784  2 snd_pcm,snd_seq

snd                    51667  5 snd_bcm2835,snd_timer,snd_pcm,snd_seq,snd_seq_device

joydev                  8903  0

evdev                   9950  1

uio_pdrv_genirq         2958  0

uio                     8119  1 uio_pdrv_genirq 

$ iwconfig --help

Usage: iwconfig [interface]

                interface essid {NNN|any|on|off}

                interface mode {managed|ad-hoc|master|...}

                interface freq N.NNN[k|M|G]

                interface channel N

                interface bit {N[k|M|G]|auto|fixed}

                interface rate {N[k|M|G]|auto|fixed}

                interface enc {NNNN-NNNN|off}

                interface key {NNNN-NNNN|off}

                interface power {period N|timeout N|saving N|off}

                interface nickname NNN

                interface nwid {NN|on|off}

                interface ap {N|off|auto}

                interface txpower {NmW|NdBm|off|auto}

                interface sens N

                interface retry {limit N|lifetime N}

                interface rts {N|auto|fixed|off}

                interface frag {N|auto|fixed|off}

                interface modulation {11g|11a|CCK|OFDMg|...}

                interface commit

       Check man pages for more details.

$ iwconfig

wlan0     IEEE 802.11bgn  ESSID:off/any

          Mode:Managed  Access Point: Not-Associated   Tx-Power=20 dBm

          Retry short limit:7   RTS thr:off   Fragment thr:off

          Power Management:off

lo        no wireless extensions.

eth0      no wireless extensions.

eth0      no wireless extensions. 

$ cat /proc/cpuinfo

processor       : 0

model name      : ARMv7 Processor rev 5 (v7l)

BogoMIPS        : 38.40

Features        : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm

CPU implementer : 0x41

CPU architecture: 7

CPU variant     : 0x0

CPU part        : 0xc07

CPU revision    : 5