司馬遷在《史記》的最後一篇《太史公自序》裡所說的

失之豪釐，差以千里

應是源自《觀測之『測天文』 》一文中，所講的那個『觀天』的『傳統』︰

……

或許出於《周髀算經》

「髀」，拼音：bì，注音：ㄅㄧˋ，也簡稱《周髀》，是中國古代一本數學專業書籍，在中國唐代收入《算經十書》，並為《十經》的第一部。

周髀的成書年代至今沒有統一的說法，有人認為是周公所作，也有人認為是在西漢末年寫成。

《周髀算經》是中國歷史上最早的一部天文曆算著作，也是中國流傳至今最早的數學著作，是後世數學的源頭，其算術化傾向決定中國數學發展的性質，歷代數學家奉為經典。

《周髀算經》《卷上》

 

的求『日高』之法，大概就是

失之豪釐，差以千里

的成因。

可以得到

然而『天很高，日很遠』，因此 ，故而很難『度量』的『精準』，一點點『角度』之『誤差』就產生了那個

失之豪釐，差以千里

的吧！！

─── 《失之豪釐，差以千里！！《上》》

 

已知軟件『風扇控制』法，在此情狀不管用。☻

既然自己焊接功夫又不好，就試試這個硬體『PoE 分離』法吧！☺

Re: PoE HAT – USB Ports not working – over-current

Grozzie

Tue Sep 04, 2018 12:28 pm

……

Re: PoE HAT – USB Ports not working – over-current

Grozzie

Wed Sep 05, 2018 5:21 pm

 

由於手上沒有那位作者之『 micro usb connector 電源供應』頭，且直接連通 5V (pin 2) 以及接地 (pin 6) 針 ，看看如何哩？！

 

一樣可以開機勒！？

此時當然『風扇』不會轉，雖然也看不到『over-current change』的蹤影︰

pi@raspberrypi:~ 

 

不過卻跑出了許多『Under-voltage detected!』訊息︰

pi@raspberrypi:~  

 

不知為什麼？？只好『從頭想』★

 

 

 

 

 

 

 

 

科學追求真理，為的是打開大自然的黑箱；然而真理明白若昭，就是透明的白箱。我們總在求真的旅途上一知半解，努力化灰箱為白箱。如果偵錯就是科學，除錯即求真理，那這一段話用在『偵錯』與『除錯』上來講依然合適。這也說明為什麼人們喜歡用不同的灰度，來表達對『箱內之物』的認識與了解了。

…

如何打開黑箱？讓我們歸結到胡適之先生的兩句名言︰

作學問要，

大膽假設，小心求證。

而讀書要，

於不疑處有疑，於有疑處不疑。

─── 《打開黑箱！！》

 

從這兩天『測試』經驗看來，『問題』來源箭指 PoE HAT 也！實質原因一時千頭萬緒？故而前往樹莓派『論壇』谷歌！！找找是否有『類似狀況』者，聽聽他們怎麼說耶？？

PoE HAT – USB Ports not working – over-current

martinrowan

Tue Aug 21, 2018 10:10 pm

[   11.661117] Bluetooth: RFCOMM socket layer initialized
[   11.661151] Bluetooth: RFCOMM ver 1.11
[   12.986076] usb 1-1.1-port2: over-current change
[   13.147084] usb 1-1-port2: over-current change
[   13.231877] usb 1-1.1-port3: over-current change
[   13.391693] usb 1-1-port3: over-current change
[   13.631851] usb 1-1-port4: over-current change
[   33.978119] usb 1-1.1-port2: over-current change
[   34.139091] usb 1-1-port2: over-current change
[   34.211769] usb 1-1.1-port3: over-current change
[   34.371756] usb 1-1-port3: over-current change
[   34.611750] usb 1-1-port4: over-current change
[  408.250020] usb 1-1.1-port2: over-current change
[  408.411057] usb 1-1-port2: over-current change
[  408.482948] usb 1-1.1-port3: over-current change
[  408.644602] usb 1-1-port3: over-current change
[  408.762133] usb 1-1.1-port2: over-current change
[  408.883014] usb 1-1-port4: over-current change
[  408.993105] usb 1-1.1-port3: over-current change
[  409.132964] usb 1-1-port2: over-current change
[  409.232949] usb 1-1.1-port2: over-current change
[  409.372938] usb 1-1-port3: over-current change

When connecting any USB device, a USB mass storage device or the Logitech wireless keyboard transceiver, messages are logged.

[  473.733117] usb 1-1.3: new high-speed USB device number 5 using dwc_otg
[  473.864020] usb 1-1.3: New USB device found, idVendor=0781, idProduct=556c
[  473.864035] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  473.864043] usb 1-1.3: Product: Firebird USB Flash Drive
[  473.864051] usb 1-1.3: Manufacturer: SanDisk
[  473.864060] usb 1-1.3: SerialNumber: 4C532000000116109085
[  473.868191] usb-storage 1-1.3:1.0: USB Mass Storage device detected
[  473.871816] scsi host0: usb-storage 1-1.3:1.0
[  473.947128] usb 1-1-port2: over-current change
[  474.042110] usb 1-1.1-port2: over-current change
[  474.183449] usb 1-1-port3: over-current change
[  474.273351] usb 1-1.1-port3: over-current change
[  474.423299] usb 1-1.3: USB disconnect, device number 5
[  474.753127] usb 1-1.3: new high-speed USB device number 6 using dwc_otg
[  474.883976] usb 1-1.3: New USB device found, idVendor=0781, idProduct=556c
[  474.883993] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  474.884001] usb 1-1.3: Product: Firebird USB Flash Drive
[  474.884009] usb 1-1.3: Manufacturer: SanDisk
[  474.884017] usb 1-1.3: SerialNumber: 4C532000000116109085
[  474.884822] usb-storage 1-1.3:1.0: USB Mass Storage device detected
[  474.885225] scsi host0: usb-storage 1-1.3:1.0
[  474.885928] usb 1-1-port4: over-current change
[  475.066003] usb 1-1.1-port2: over-current change
[  475.123277] usb 1-1-port2: over-current change
[  475.303252] usb 1-1.1-port3: over-current change
[  475.363319] usb 1-1-port3: over-current change
[  475.603178] usb 1-1.3: USB disconnect, device number 6
[  475.903134] usb 1-1.3: new high-speed USB device number 7 using dwc_otg
[  476.044024] usb 1-1.3: New USB device found, idVendor=0781, idProduct=556c
[  476.044042] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  476.044050] usb 1-1.3: Product: Firebird USB Flash Drive
[  476.044059] usb 1-1.3: Manufacturer: SanDisk
[  476.044067] usb 1-1.3: SerialNumber: 4C532000000116109085
[  476.044877] usb-storage 1-1.3:1.0: USB Mass Storage device detected
[  476.048170] scsi host0: usb-storage 1-1.3:1.0
[  476.049075] usb 1-1-port4: over-current change
[  476.283387] usb 1-1-port2: over-current change
[  476.346097] usb 1-1.1-port2: over-current change
[  476.523476] usb 1-1-port3: over-current change
[  476.583383] usb 1-1.1-port3: over-current change
[  476.763258] usb 1-1.3: USB disconnect, device number 7
[  477.103133] usb 1-1.3: new high-speed USB device number 8 using dwc_otg
[  477.234021] usb 1-1.3: New USB device found, idVendor=0781, idProduct=556c
[  477.234038] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  477.234047] usb 1-1.3: Product: Firebird USB Flash Drive
[  477.234056] usb 1-1.3: Manufacturer: SanDisk
[  477.234064] usb 1-1.3: SerialNumber: 4C532000000116109085
[  477.234868] usb-storage 1-1.3:1.0: USB Mass Storage device detected
[  477.237752] scsi host0: usb-storage 1-1.3:1.0
[  477.238749] usb 1-1-port4: over-current change
[  478.314404] scsi 0:0:0:0: Direct-Access     SanDisk  Ultra            1.26 PQ: 0 ANSI: 5
[  478.316594] sd 0:0:0:0: [sda] 31266816 512-byte logical blocks: (16.0 GB/14.9 GiB)
[  478.317631] sd 0:0:0:0: [sda] Write Protect is off
[  478.317649] sd 0:0:0:0: [sda] Mode Sense: 43 00 00 00
[  478.318064] sd 0:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[  478.331456]  sda: sda1
[  478.334032] sd 0:0:0:0: [sda] Attached SCSI removable disk
[  478.340700] sd 0:0:0:0: Attached scsi generic sg0 type 0
[  478.394088] usb 1-1.1-port2: over-current change
[  478.555097] usb 1-1-port2: over-current change
[  478.633379] usb 1-1.1-port3: over-current change
[  479.183155] usb 1-1.3: reset high-speed USB device number 8 using dwc_otg
[  479.313802] usb 1-1-port3: over-current change
[  479.553522] usb 1-1-port4: over-current change
[  479.674094] usb 1-1.1-port2: over-current change
[  479.793515] usb 1-1-port2: over-current change
[  479.913413] usb 1-1.1-port3: over-current change
[  480.153155] usb 1-1.3: reset high-speed USB device number 8 using dwc_otg
[  480.283764] usb 1-1-port3: over-current change
[  480.442136] usb 1-1.1-port2: over-current change
[  480.603102] usb 1-1-port2: over-current change
[  480.673471] usb 1-1.1-port3: over-current change
[  481.153129] usb 1-1.3: reset high-speed USB device number 8 using dwc_otg
[  481.283588] usb 1-1-port3: over-current change
[  481.533586] usb 1-1-port4: over-current change

Checking my Cisco SG250-26HP switch shows the port connected to the Pi (via a 1m cable):

• Operational Status: Delivering Power
• Administrative Power Allocation: 30000mW
• Power Consumption: 3000mW
• Class: 3
• PoE Standard: 802.3 AT

Do I have a faulty HAT, or RPi3, or any other suggestions as to why this isn’t working properly. When powered via micro USB power socket the USB ports work just fine.

……

 

多方文字洋洋灑灑，似乎已將『硬體』定罪矣！！？？

不過一時『科南』上身？？！！

─── 摘自《胡楊三千！！》

 

竟敢先『履虎尾』乎，

Re: PoE HAT – USB Ports not working – over-current

scripsi

Thu Sep 06, 2018 3:00 pm

echo 40 | sudo tee /sys/class/hwmon/hwmon0/def_pwm1

Which worked – the errors went away and I was succesfully able to mount the USB drive – but didn’t survive a reboot. So I tried the change to the rpi-poe overlay detailed above which also worked and survived a reboot.

While this temporary kludge helps me get on with developing my solution, I wouldn’t feel confident putting it into a production environment! It’s a shame – I hope that we can find a more permanent fix.

……

Re: PoE HAT – USB Ports not working – over-current

bfarmerjr

Fri Sep 07, 2018 5:07 pm

 

發現它會咬人哩★

pi@raspberrypi:~  

 

 

 

 

 

 

 

 

『窮舉法』是一種通用方法。它以『問題』為『解』之『對錯』的『判準』，窮盡『所有可能』的『解』作『斷言』之求解法。或可同時參閱《 M♪o 之學習筆記本《寅》井井︰【䷝】試釋是事》文中所說之『蠻力法』以及例子︰

☿ 行︰雖說是蠻力法，實則乃用『窮舉』，數ㄕㄨˇ數ㄕㄨˋ數不盡，耗時難為功，怎曉 機心迅捷後，此法遂真可行耶！？實習所用機，登入採『學號』與『針碼』【※ Pin Code 四位數字碼】 。『學號』之制 ── 班碼-位碼 ──，班不過十，位少於百，故而極其數不足千。針碼有四位，總其量，只有萬。試而盡之，『千萬』已『窮舉』。問題當在『咸澤碼訊』有多快？『登錄』之法有 多嚴 ？破解程式幾人會？設使一應具足，那個『駭黑』之事，怕是恐難免！！……

此處特別指出計算機『速度提昇』使得『窮舉法』的實用性大增，對此法的了解也就更顯得重要了。

假使將『所有可能解』看成『解空間』，將『問題』當成『約束』條件，此時『問題』的『求解』，就轉換成『尋找』『解空間』中滿足『約束』條件的『解』。一般將之稱為『蠻力搜尋法』︰

Brute-force search

In computer science, brute-force search or exhaustive search, also known as generate and test, is a very general problem-solving technique that consists of systematically enumerating all possible candidates for the solution and checking whether each candidate satisfies the problem’s statement.

A brute-force algorithm to find the divisors of a natural number n would enumerate all integers from 1 to the square root of n, and check whether each of them divides n without remainder. A brute-force approach for the eight queens puzzle would examine all possible arrangements of 8 pieces on the 64-square chessboard, and, for each arrangement, check whether each (queen) piece can attack any other.

While a brute-force search is simple to implement, and will always find a solution if it exists, its cost is proportional to the number of candidate solutions – which in many practical problems tends to grow very quickly as the size of the problem increases. Therefore, brute-force search is typically used when the problem size is limited, or when there are problem-specific heuristics that can be used to reduce the set of candidate solutions to a manageable size. The method is also used when the simplicity of implementation is more important than speed.

This is the case, for example, in critical applications where any errors in the algorithm would have very serious consequences; or when using a computer to prove a mathematical theorem. Brute-force search is also useful as a baseline method when benchmarking other algorithms or metaheuristics. Indeed, brute-force search can be viewed as the simplest metaheuristic. Brute force search should not be confused with backtracking, where large sets of solutions can be discarded without being explicitly enumerated (as in the textbook computer solution to the eight queens problem above). The brute-force method for finding an item in a table — namely, check all entries of the latter, sequentially — is called linear search.

─── 《勇闖新世界︰ 《 PYDATALOG 》【專題】之約束編程‧三》

 

心想碰到『古怪』之事！如何『決斷』咦？最好用『窮舉』法☺

電源甲乙丙︰

‧ A/C Adapter

‧ PoE Splitter

‧ Official PoE HAT

情況有三種︰

‧ SD boot

‧ USB Flash connected via Power HUB, then Boot

‧ USB Flash  connected directly to Raspberry Pi, then Boot

 

同時確認官網『啟動流程』文件︰

BOOT FLOW

The flow of boot begins with reading the OTP to decide on the valid boot modes enabled. By default, this is SD card boot followed by USB device boot. Subsequently, the boot ROM checks to see if the GPIO boot mode OTP bits have been programmed — one to enable GPIO boot mode and one to select the bank of GPIOs it uses to disable boot modes (low = GPIOs 22-26, high = GPIOs 39-43). This makes it possible to use a hardware switch to choose between different boot modes if there is more than one available.

The GPIO boot mode OTP bits can be programmed by adding program_gpio_bootmode=n to config.txt, where n is 1 to select the low bank (22-26) or 2 to select the high bank (39-43). Once added, boot the device, then power-cycle it (rebooting is not sufficient). You should expect it to no longer boot (all boot modes will be disabled by default). Apply a pull-up to the required pin to enable the required boot mode. After programming, the config.txt setting can be removed.

N.B.:

1. It is important to remember that, once set, OTP bits can never be unset, so think carefully before enabling this facility because it effectively makes 5 GPIOs unusable for other purposes. Also note that the bit assignments make it possible to switch from the low bank (22-26) to the high bank (39-43), but not back again, and that selecting the high bank is likely to produce a non-bootable Pi, unless you’re using a Compute Module (any version).
2. Do not use program_gpio_bootmode unless your firmware is dated 20 Oct 2017 or later (vcgencmd version). Doing so will make it impossible to select the low bank of boot mode GPIOs.

Next the boot ROM checks each of the boot sources for a file called bootcode.bin; if it is successful it will load the code into the local 128K cache and jump to it. The overall boot mode process is as follows:

• 2837 boots
• Reads boot ROM enabled boot modes from OTP
• Uses program_gpio_bootmode to disable some modes by reading GPIOs 22-26 or 39-43 to see if the default values do not equal the default pull to ‘0’. If it is low, it will disable that boot mode for each of SD1, SD2, NAND, SPI, USB. If the value read is a ‘1’, then that boot mode is enabled (note this cannot enable boot modes that have not already been enabled in the OTP). The default pull resistance is around 50K ohm, so a smaller pull up of 5K should suffice to enable the boot mode but still allow the GPIO to be operational without consuming too much power.
• If enabled: check primary SD for bootcode.bin on GPIO 48-53
  • Success – Boot
  • Fail – timeout (five seconds)
• If enabled: check secondary SD
  • Success – Boot
  • Fail – timeout (five seconds)
• If enabled: check NAND
• If enabled: check SPI
• If enabled: check USB
  • If OTG pin == 0
  • Enable USB, wait for valid USB 2.0 devices (two seconds)
    • Device found:
    • If device type == hub
      • Recurse for each port
    • If device type == (mass storage or LAN951x)
      • Store in list of devices
  • Recurse through each MSD
    • If bootcode.bin found boot
  • Recurse through each LAN951x
    • DHCP / TFTP boot
  • else (Device mode boot)
  • Enable device mode and wait for host PC to enumerate
  • We reply to PC with VID: 0a5c PID: 0x2763 (Pi 1 or Pi 2) or 0x2764 (Pi 3)

NOTES:

• If there is no SD card inserted, the SD boot mode takes five seconds to fail. To reduce this and fall back to USB more quickly, you can either insert an SD card with nothing on it or use the GPIO bootmode OTP setting described above to only enable USB.
• The default pull for the GPIOs is defined on page 102 of the ARM Peripherals datasheet. If the value at boot time does not equal the default pull, then that boot mode is enabled.
• USB enumeration is a means of enabling power to the downstream devices on a hub, then waiting for the device to pull the D+ and D- lines to indicate if it is either USB 1 or USB 2. This can take time: on some devices it can take up to three seconds for a hard disk drive to spin up and start the enumeration process. Because this is the only way of detecting that the hardware is attached, we have to wait for a minimum amount of time (two seconds). If the device fails to respond after this maximum timeout, it is possible to increase the timeout to five seconds using program_usb_boot_timeout=1 in config.txt.
• MSD takes precedence over Ethernet boot.
• It is no longer necessary for the first partition to be the FAT partition, as the MSD boot will continue to search for a FAT partition beyond the first one.
• The boot ROM also now supports GUID partitioning and has been tested with hard drives partitioned using Mac, Windows, and Linux.
• The LAN951x is detected using the Vendor ID 0x0424 and Product ID 0xec00, this is different to the standalone LAN9500 device which has a product ID of 0x9500 or 0x9e00. To use the standalone LAN9500 an I2C EEPROM would need to be added to change these ID’s to match the LAN9514

The primary SD card boot mode is, as standard, set to be GPIOs 49-53. It is possible to boot from the secondary SD card on a second set of pins, i.e. to add a secondary SD card to the GPIO pins. However, we have not yet enabled this ability.

NAND boot and SPI boot modes do work, although they do not yet have full GPU support.

The USB device boot mode is enabled by default at the time of manufacture, but the USB host boot mode is only enabled with program_usb_boot_mode=1. Once enabled, the processor will use the value of the OTGID pin on the processor to decide between the two modes. On a Raspberry Pi Model B, the OTGID pin is driven to ‘0’ and therefore will only boot via host mode once enabled (it is not possible to boot through device mode because the LAN9515 device is in the way).

The USB will boot as a USB device on the Pi Zero or Compute Module if the OTGID pin is left floating (when plugged into a PC for example), so you can ‘squirt’ the bootcode.bin into the device. The code for doing this is usbboot.

 

為何一切行禮如儀，十之八九如其所言，可是唯獨

Official PoE HAT + USB Flash  connected directly to Raspberry Pi, then Boot

這個組合卻不行呢？☻

 

 

 

 

 

 

 

 

『科學精神』意在求真，大概不需要『詭辯矛盾』之非吧！

『技術創新』追求圓滿，終究免不了『善惡美醜』之是哩！

故爾針對

Under-voltage detected! (0x00050005) … how to disable?

文本之『硬體』和『軟件』及其『偵測訊息』該與不該對誰顯示的問題，理當置於『是是非非』之外乎？

不巧人間『價值衝突』常有『是其所非，非其所是』之爭耶？？

所以借著

Under-voltage detected! (0x00050005) spams dmesg on new kernel 4.14.30-v7+ #2512

書己一二成見，非為議論呦！！

─── 《STEM 隨筆︰古典力學︰轉子【五】《電路學》三【電阻】V.E》

 

俗語說︰飯可以多吃，話不要鐵齒！

昨天才講測好了 POE + SD 卡，今天一試 USB 『大拇哥』卻不行？

分明 POE 『規格』清清楚楚︰

RASPBERRY PI POE HAT

The Raspberry Pi PoE HAT is an add-on board for the Raspberry Pi 3 Model B+. It allows the Raspberry Pi to be powered via a power-enabled Ethernet network.

• 802.3af PoE
• Fully isolated switched-mode power supply
• 37–57V DC, Class 2 device
• 5V/2.5A DC output
• 25mm x 25mm brushless fan for processor cooling
• Fan control

PRODUCT BRIEF AND MECHANICAL DRAWINGS

• Raspberry Pi PoE HAT product brief
• Raspberry Pi PoE HAT mechanical drawing

 

怎麼卻不給用呢？！

HOW TO BOOT FROM A USB MASS STORAGE DEVICE ON A RASPBERRY PI 3

This tutorial explains how to boot your Raspberry Pi 3 from a USB mass storage device such as a flash drive or USB hard disk. Be warned that this feature is experimental and does not work with all USB mass storage devices. See this blog post from Gordon Hollingworth for an explanation of why some USB mass storage devices don’t work, as well as some background information.

Program USB Boot Mode

Before a Raspberry Pi 3 will boot from a mass storage device, it needs to be booted from an SD card with a config option to enable USB boot mode. This will set a bit in the OTP (One Time Programmable) memory in the Raspberry Pi SoC that will enable booting from a USB mass storage device. Once this bit has been set, the SD card is no longer required. Note that any change you make to the OTP is permanent and cannot be undone.

You can use any SD card running Raspbian or Raspbian Lite to program the OTP bit. If you don’t have such an SD card then you can install Raspbian or Raspbian Lite in the normal way – see installing images.

First, prepare the /boot directory with up to date boot files:

 vcgencmd otp_dump | grep 17:
17:3020000a

Ensure the output 0x3020000a is shown. If it is not, then the OTP bit has not been successfully programmed.

If you wish, you can remove the program_usb_boot_mode line from config.txt, so that if you put the SD card in another Raspberry Pi, it won’t program USB boot mode. Make sure there is no blank line at the end of config.txt. You can edit config.txt using the nano editor using the command sudo nano /boot/config.txt, for example.

Prepare the USB mass storage device

Starting with the 2017-04-10 release of Raspbian you can install a working Raspbian system to a USB mass storage device by copying the operating system image directly onto your USB device, in the same way that you would for an SD card. To perform this step, follow the instructions here, remembering to select the drive that corresponds to your USB mass storage device.

Once you have finished imaging your USB mass storage device, remove it from your computer and insert it into your Raspberry Pi 3.

Boot your Raspberry Pi 3 from the USB mass storage device

Attach the USB mass storage device to your Raspberry Pi 3 and power it up. After between five and ten seconds the Raspberry Pi 3 should begin booting, and display the rainbow splash screen on an attached screen.

 

不是早已成『預設』？？況且也看到 rainbow splash 的呦！！

莫非真遇着『相容性』問題的吧！！？？

PI 3 BOOTING PART I: USB MASS STORAGE BOOT BETA

 

When we originally announced the Raspberry Pi 3, we announced that we’d implemented several new boot modes. The first of these is the USB mass storage boot mode, and we’ll explain a little bit about it in this post; stay tuned for the next part on booting over Ethernet tomorrow. We’ve also supplied a boot modes tutorial over on the Raspberry Pi documentation pages.

Note: the new boot modes are still in beta testing and use the “next” branch of the firmware. If you’re unsure about using the new boot modes, it’s probably best to wait until we release it fully.

How did we do this?

Inside the 2835/6/7 devices there’s a small boot ROM, which is an unchanging bit of code used to boot the device. It’s the boot ROM that can read files from SD cards and execute them. Previously, there were two boot modes: SD boot and USB device boot (used for booting the Compute Module). When the Pi is powered up or rebooted, it tries to talk to an attached SD card and looks for a file called bootcode.bin; if it finds it, then it loads it into memory and jumps to it. This piece of code then continues to load up the rest of the Pi system, such as the firmware and ARM kernel.

While squeezing in the Quad A53 processors, I spent a fair amount of time writing some new boot modes. If you’d like to get into a little more detail, there’s more information in the documentation. Needless to say, it’s not easy squeezing SD boot, eMMC boot, SPI boot, NAND flash, FAT filesystem, GUID and MBR partitions, USB device, USB host, Ethernet device, and mass storage device support into a mere 32kB.

What is a mass storage device?

The USB specification allows for a mass storage class which many devices implement, from the humble flash drive to USB attached hard drives. This includes micro SD readers, but generally it refers to anything you can plug into a computer’s USB port and use for file storage.

I’ve tried plugging in a flash drive before and it didn’t do anything. What’s wrong? 

We haven’t enabled this boot mode by default, because we first wanted to check that it worked as expected. The boot modes are enabled in One-Time Programmable (OTP) memory, so you have to enable the boot mode on your Pi 3 first. This is done using a config.txt parameter.

Instructions for implementing the mass storage boot mode, and changing a suitable Raspbian image to boot from a flash drive, can be found here.

Are there any bugs / problems?

There are a couple of known issues:

1. Some flash drives power up too slowly. There are many spinning disk drives that don’t respond within the allotted two seconds. It’s possible to extend this timeout to five seconds, but there are devices that fail to respond within this period as well, such as the Verbatim PinStripe 64GB.
2. Some flash drives have a very specific protocol requirement that we don’t handle; as a result of this, we can’t talk to these drives correctly. An example of such a drive would be the Kingston Data Traveller 100 G3 32G.

These bugs exist due to the method used to develop the boot code and squeeze it into 32kB. It simply wasn’t possible to run comprehensive tests.

However, thanks to a thorough search of eBay and some rigorous testing by our awesome work experience student Henry Budden, we’ve found the following devices work perfectly well:

• Sandisk Cruzer Fit 16GB
• Sandisk Cruzer Blade 16Gb
• Samsung 32GB USB 3.0 drive
• MeCo 16GB USB 3.0

If you find some devices we haven’t been able to test, we’d be grateful if you’d let us know your results in the comments.

Will it be possible to boot a Pi 1 or Pi 2 using MSD?

Unfortunately not. The boot code is stored in the BCM2837 device only, so the Pi 1, Pi 2, and Pi Zero will all require SD cards.

However, I have been able to boot a Pi 1 and Pi 2 using a very special SD card that only contains the single file bootcode.bin. This is useful if you want to boot a Pi from USB, but don’t want the possible unreliability of an SD card. Don’t mount the SD card from Linux, and it will never get corrupted!

My MSD doesn’t work. Is there something else I can do to get it working?

If you can’t boot from the MSD, then there are some steps that you can take to diagnose the problem. Please note, though, this is very much still a work in progress:

• Format an SD card as FAT32
• Copy the current next branch bootcode.bin from GitHub onto the SD card
• Plug it into the Pi and try again

If this still doesn’t work, please open an issue in the firmware repository.

 

只是為何 POE + w/Power HUB + 大拇哥又 OK 靁？？！！