據聞在結冰的湖面上『打水漂』，鳥鳴聲啾啾！一篇在 Make: 雜誌上的癹文 POST ，能叫樹莓派 3 著火︰

The Raspberry Pi 3 Does Not Halt and Catch Fire

March 2, 2016, 11:25 am PST

Thermal image of the Raspberry Pi 3. (Credit: Gareth Halfacree)

Earlier today Gareth Halfacree, author of the Raspberry Pi User Guide, posted some really interesting thermal images of the new Raspberry Pi 3 board on Reddit. However worryingly, not only was Gareth measuring temperatures in excess of 100°C (212°F) under load for the BCM2837, but also measuring an offset of a full 17°C between his own measurements and the readings generated by the internal temperature sensor on the chip.

“The new BCM2837 system-on-chip gets far, far hotter than its predecessors. This image was taken using a calibrated Flir thermal camera while the Pi 3 had been at 100% CPU load – but no GPU load – for five minutes, and registered nearly 100°C (212°F). I confirmed the temperature with a K-type contact probe, and also by poking the chip. Don’t poke the chip. It hurts.” — Gareth Halfacree

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此文一出，立刻催生了論壇的熱議︰

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嗆的樹莓派教主趕快在 ZDNet 上滅火︰

No, your Raspberry Pi 3 won’t overheat in everyday use, says its creator

The Raspberry Pi Foundation founder says most users will never see their board reach anywhere near the 100C reported by some running heavy duty benchmarks on the Pi.

By Nick Heath | March 4, 2016 — 17:30 GMT (01:30 GMT+08:00) | Topic: Hardware

The Raspberry Pi 3 will not overheat in regular use, the board’s co-creator has said, following reports of the newly released $35 computer hitting close to 100C during tests.

When benchmarking the board, some owners reported the Pi 3 heated up to the point where it reduced its speed in order to keep its temperature in check.

However, co-creator of the board Eben Upton has said that – outside of synthetic tests that place the board’s processor under prolonged strain – the Pi 3 is highly unlikely to behave in this way.

“In everyday use I would say ‘never’,” he said in response to a question about how often boards would reach temperatures where they need to throttle their speed.

He points out that the spikes in temperature reported by these users stem from benchmarks where the Pi’s processor is put under sustained heavy load – in this case using the benchmark sysbench to calculate prime numbers.

The strain placed on the board during these benchmarks – where the CPU is subject to prolonged heavy demand – isn’t representative of workloads that will be placed on the processor in everyday use.

While a typical workload for the Pi might see the demand on the CPU spike momentarily, in the vast majority of use cases these periods of high CPU utilisation will not be sustained for long periods, he said.

“In most use cases you see a very spiky performance profile. So what you’re looking at is ‘Can I run very fast for a second?’ or ‘Can I run very fast in bunches of 50ms?’.”

And while putting a case on the board will increase the temperature, again for the typical user it will not drive the board to become hot enough to throttle its speed – he said.

Upton explains the throttling behavior as being a consequence of making the Pi’s hardware more powerful.

“It’s the difference between Raspberry Pi 1, with a relatively small amount of processing power, and Raspberry Pi 3 with 10x that amount of processing power. As we get towards laptop levels of performance we have to apply the same sort of techniques you apply for managing the thermals [in a laptop].”

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偏偏講的不清不楚似有若無，彷彿樹莓派 3 有十倍速，所以…… 才火紅？？！！

雖然作者沒有『熱像儀』可以拍照，只好用著『谷歌考古』的辦法找出歷史上之樹莓派『存證』︰

【Raspberry Pi Model B】

【Raspberry Pi Model 2B】

比較下，著實覺得『很可疑』︰

【Raspberry Model 3B】

，此照宛如『出火』一般︰

，不知此景只得『哪裡有』！！？？

僅就電子裝置的『熱設計』與『熱管理』而言︰

Thermal management (electronics)

All electronic devices and circuitry generate excess Heat and thus require thermal management to improve reliability and prevent premature failure. The amount of heat output is equal to the power input, if there are no other energy interactions.^[1] There are several techniques for cooling including various styles of heat sinks, thermoelectric coolers, forced air systems and fans, heat pipes, and others.

In cases of extreme low environmental temperatures, it may actually be necessary to heat the electronic components to achieve satisfactory operation.^[2]

60×60×10 mm straight-finned heat sink with a thermal profile and swirling animated forced convection flow trajectories from a tubeaxial fan, predicted using a CFD analysis package.

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從第一代就可以玩『超頻』的樹莓派︰

───

焉有不知之理耶？？？

假使不擔心『保固』，強制『升壓』和『超頻』又何妨︰

Overclocking

NOTE: Setting parameters other than that available by ‘raspi-config’ will set a permanent bit within the SoC, making it possibly to detect that you Raspberry Pi has been overclocked. This was meant to void warranty if the device has been overclocked. Since 19th of September 2012 you can overclock your Raspberry Pi without affecting your warranty^[2]

The latest kernel has a cpufreq kernel driver with the “ondemand” governor enabled by default. It has no effect if you have no overclock settings. But when you do, the arm frequency will vary with processor load. Non default values are only used when needed according to the used governor. You can adjust the minimum values with the *_min config options or disable dynamic clocking with force_turbo=1. ^[3]

Overclock and overvoltage will be disabled at runtime when the SoC reaches 85 °C to cool it down. You should not hit the limit, even with maximum settings at 25 °C ambient temperature. ^[4]

Overclocking options

……

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只不過如果不仔細了解一下，所謂的︰

Dynamic frequency scaling

Dynamic frequency scaling (also known as CPU throttling) is a technique in computer architecture whereby the frequency of a microprocessor can be automatically adjusted “on the fly,” either to conserve power or to reduce the amount of heat generated by the chip. Dynamic frequency scaling is commonly used in laptops and other mobile devices, where energy comes from a battery and thus is limited. It is also used in quiet computing settings and to decrease energy and cooling costs for lightly loaded machines. Less heat output, in turn, allows the system cooling fans to be throttled down or turned off, reducing noise levels and further decreasing power consumption. It is also used for reducing heat in insufficiently cooled systems when the temperature reaches a certain threshold, such as in poorly cooled overclocked systems.

The dynamic power (switching power) dissipated per unit of time by a chip is C·V²·A·f, where C is the capacitance being switched per clock cycle, V is voltage, A is the Activity Factor^[1] indicating the average number of switching events undergone by the transistors in the chip (as a unitless quantity) and f is the switching frequency.^[2] The voltage required for stable operation is determined by the frequency at which the circuit is clocked, and can be reduced if the frequency is also reduced.^[3] Dynamic power does not account for the total power of the chip, however, as there is also static power, which is primarily because of various leakage currents. Due to static power consumption and asymptotic execution time it has been shown that the energy consumption of a piece of software shows convex energy behavior, i.e., there exists an optimal CPU frequency at which energy consumption is minimal.^[4] Leakage current has become more and more important as transistor sizes have become smaller and threshold voltage levels lower. A decade ago, dynamic power accounted for approximately two-thirds of the total chip power. The power loss due to leakage currents in contemporary CPUs and SoCs tend to dominate the total power consumption. In the attempt to control the leakage power high-k metal-gates and power gating have been common methods.

Dynamic voltage scaling is another power conservation technique that is often used in conjunction with frequency scaling, as the frequency that a chip may run at is related to the operating voltage.

The efficiency of some electrical components, such as voltage regulators, decreases with increasing temperature, so the power used may increase with temperature. Since increasing power use may increase the temperature, increases in voltage or frequency may increase system power demands even further than the CMOS formula indicates, and vice versa.^[5][6]

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以及

CPU power dissipation

Sources

There are several factors contributing to the CPU power consumption; they include dynamic power consumption, short-circuit power consumption, and power loss due to transistor leakage currents:

The dynamic power consumption originates from the activity of logic gates inside a CPU. When the logic gates toggle, energy is flowing as the capacitors inside them are charged and discharged. The dynamic power consumed by a CPU is approximately proportional to the CPU frequency, and to the square of the CPU voltage:^[5]

where C is capacitance, f is frequency, and V is voltage.

When logic gates toggle, some transistors inside may change states. As this takes a finite amount of time, it may happen that for a very brief amount of time some transistors are conducting simultaneously. A direct path between the source and ground then results in some short-circuit power loss. The magnitude of this power is dependent on the logic gate, and is rather complex to model on a macro level.

Power consumption due to leakage power emanates at a micro-level in transistors. Small amounts of currents are always flowing between the differently doped parts of the transistor. The magnitude of these currents depend on the state of the transistor, its dimensions, physical properties and sometimes temperature. The total amount of leakage currents tends to inflate for increasing temperature and decreasing transistor sizes.

Both dynamic and short-circuit power consumption are dependent on the clock frequency, while the leakage current is dependent on the CPU supply voltage. It has been shown that the energy consumption of a program shows convex energy behavior, meaning that there exists an optimal CPU frequency at which energy consumption is minimal.^[6]

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就怕樹莓派它『真燒掉』的哩！！！

打從一開始以來，樹莓派就種下了『電源』傳聞之因︰

雖然今天樹莓派已廣為流行, 賣了數百萬台. 你依然需要注意選用的電源供應器. 考察 樹莓派的原始設計:  如 Raspberry-Pi-R2.0-Schematics-Issue2.2_027.pdf , 512M Rev.B  上所說,  F3 保險絲的電阻大約 是 0.28 Ohms, 一般典型使用約為 700mA, 那壓降為 0.196V. 正如網路上曾說好的樹莓派電源供應器,  輸出電壓為 5.25V, 事實是正為了補償壓降損失而來, 才能使 TP1-TP2 間的電壓接近 5V.  如果再考慮供應電線的阻抗, 以及USB其它裝置的供電, TP1-TP2 間的電壓或許將在 5V +- 5% 區間之外, 以致引發某些 USB 裝置的工作不正常.

─── 引用《欲善其事, 先利其器: 樹莓派的電源》

雖說其後 B+ 『電源』的設計已經改善，然而還有人使用『充電器』這類的『電源』，由於線材電阻對充電器而言比較不重要，通常都在容許範圍裡。但是電阻過高，使用的電流越大，這個『壓降』會導致樹莓派工作不正常。更不要講又有 USB 埠供電 600 mA 或 1.2 A

max_usb_current=1

config.txt 組構所引起的麻煩︰

Testing & Setting the USB current limiter on the Raspberry Pi B+

safe_mode_gpio=4

max_usb_current=1

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真是講不清、理還亂，所以現今樹莓派論壇又開始討論︰

Pi 3 power supply & USB cable

……

……

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此處典型的開機實測結果 ── 只接 USB 鍵盤、滑鼠 ── ，類似 MagPi 雜誌文本內容一般︰

Raspberry Pi 3 is out now! Specs, benchmarks & more

You can’t get extra performance without a few sacrifices. The Pi 3 draws the most power of the test group, but its extra performance means it spends more time at idle. Those looking for maximum battery life should look at the Model A+ or the Pi Zero as an alternative.

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作者不知樹莓派官網建議的 5V/2.5A 是否分配為傳聞所說的

1A SoC/RAM

0.3A WiFi/BT

1.2A USB ※ max_usb_current=1

，不過認為這是合理的規劃。

假使遭遇『不開機』的狀況，首先拔除所有 USB 的裝置，使用預設的組構檔 config.txt ，確認是否能夠開機？若是不行，那麼大概就是『電源』的問題了！若是說『電源』的 V/A 標示值應該沒有問題，那麼就可能是『電源線』之『材質』、『線徑』、『線長』引起的『壓降』產生的！！這時若想要確認只有實際『量測』一途。就像在《音樂播放器之 CD 轉成 mp3《三》上》文本中所說之嘗試驗證 USB DVD 讀寫裝置的電源需求一樣︰

也許可以說『測試』就是用『程式』所允許的『輸入』 Input ，打敗該『程式』之『程序』 Process 之『工藝』。進一步『除錯』，就是嘗試《打開黑箱！！》，找到『原因』並且解決『錯誤』的『活動』。因此於『設計程式』之前，我們需要先『確定』那些使用在『音樂播放器』之『原型機』上的『設備』和『軟體』都『正確無誤』，以及為將來可能的『變更』預做打算。舉例來說，我們如何測試『 USB DVD 讀寫裝置』呢？從這個裝置有兩個 USB 連接頭來看，它是一種耗電量大於 5V 500mA 的裝置，所以才需要兩個『 USB 埠』來供電。其實這也是作者選擇 B+ 而不是 B 的最主要原因， B+ 有四個 USB 埠以及改良過的供電迴路設計。因此只用

lsusb
Bus 001 Device 007: ID 0411:01dc BUFFALO INC. (formerly MelCo., Inc.)

dmesg | grep sr0
[216848.833462] sr0: scsi3-mmc drive: 8x/24x writer dvd-ram cd/rw xa/form2 cdda tray
[216848.838233] sr 0:0:0:0: Attached scsi CD-ROM sr0

，雖然能夠知道 raspbian 認識這個裝置，並不代表它就能夠正常工作。然而確定一個『裝置』或『系統』的【電源需求】，一般需要長時間以及各種操作樣態下的『消耗功率』量測。事實這是十分困難而且麻煩的事情，所以人們多半僅參考產品之『功率規格』來『確認』這件事。有時當系統發生『時好時壞』的狀況時，這個【電源問題】就成了最難診斷的『疑難』之一，更不要講那些用『電池』供電的系統的了。

由此我們可以知道，這一個『 USB DVD 讀寫裝置』的消耗功率『變化很大』，假使思考『可靠性設計』的問題，我們需要明白『最大瞬間功率』 ── 紅色數據 ── 的需求，否則可能的系統『不穩定性』就會暗藏其中，日後當系統出狀況時，也許很難追查『原因』。讀者自當可以發現 『 USB 埠傳輸功率量測』裝置的『資料輸出格式』真很『簡潔清楚』的吧！

Hearsay

Hearsay evidence is “an out-of-court statement introduced to prove the truth of the matter asserted therein.” In certain courts hearsay evidence is inadmissible (the “Hearsay Evidence Rule”) unless an exception to the Hearsay Rule applies.

For example, to prove Tom was in town, the attorney asks a witness, “What did Susan tell you about Tom being in town?” Since the witness’ answer will rely on an out-of-court statement that Susan made, Susan is not available for cross-examination, and it is to prove the truth that Tom was in town, it is hearsay. A justification for the objection is that the person who made the statement is not in court and thus is insulated from cross examination. Note, however, that if the attorney asking the same question is trying to prove not the truth of the assertion about Tom being in town but the fact that Susan said the specific words, it may be acceptable. For example, it would be acceptable to ask a witness what Susan told them about Tom in a defamation case against Susan because now the witness is asked about the opposing party’s statement that constitutes a verbal act.^[1][2]

The hearsay rule does not exclude the evidence if it is an operative fact^{[clarification needed]}. Language of commercial offer and acceptance is also admissible over a hearsay exception because the statements have independent legal significance.

Double hearsay is a hearsay statement that contains another hearsay statement itself.

For example, a witness wants to testify that “a very reliable man informed me that Wools-Sampson told him.” The statements of the very reliable man and Wools-Sampson are both hearsay submissions on the part of the witness, and the second hearsay (the statement of Wools-Sampson) depends on the first (the statement of the very reliable man). In a court, both layers of hearsay must be found separately admissible. In this example, the first hearsay also comes from an anonymous source, and the admissibility of an anonymous statement requires additional legal burden of proof.

Many jurisdictions that generally disallow hearsay evidence in courts permit the more widespread use of hearsay in non-judicial hearings.

……

傳聞證據排除法則

傳聞證據排除法則，是刑事訴訟法上，判斷是否應排除傳聞證據的理論，即不採「傳聞證據」之法則。應與之區別者，為「傳聞法則 」。傳聞法則是指「規範傳聞證據資料使用與否之法則」，其中以排除為原則，使用為例外，因為「法則」當中，一定包含「原則」與「例外」。因此，傳聞證據排除法則，其實是「傳聞法則」的一部分，也就是傳聞法則的「原則」而已。所謂傳聞證據，原指「傳聞供述證據」，即內容為證人之陳述，供述者僅轉述證人之陳述，現泛指「證人之書面傳聞」與「證人之證人傳聞」。

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自從之前編輯《時間線︰樹莓派發展簡史》以來，已過了五、六百個日子的了？也許早該重新修繕的吧！然在如何重編一事，卻一直沒有好想法 ，這其間每次樹莓派基金會『新發行』之時常有各種『傳聞』 Hearsay 。回想自己幾年來因好奇貪玩，故常接觸『☆★之火』說法，何不說說幾則『經驗』，雖算不得『 □ ○ 傳聞』 之思辨，或可傳達『科學』誠該建立在『實證』基礎上的乎？！

【樹莓派 3 到底是 哪裡生產的？？】

依據『 elinux.org 』之整理列表︰

應該是『 Mfg by Sony 』，再考之以『歷史』之『名詞解釋』︰

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當然是『 U.K. 』英國的咯！！但是這真的很重要嗎？？就像很多人都知道『蘋果手機』是『鴻海大陸廠』製造的，這難到是『傳聞』嗎？？！！還是說如此它就會有『品質疑慮』的呢！！？？……

事實上，『良心事業』從來沒有個『古今東西』之別的吧！

『樹莓派 3 』上實際驗證『版本碼』如下︰

cat /proc/cpuinfo | grep 'Revision' | awk '{print  cat /proc/version 
Linux version 4.1.19-v7+ (dc4@dc4-XPS13-9333) (gcc version 4.9.3 (crosstool-NG crosstool-ng-1.22.0-88-g8460611) ) #852 SMP Mon Mar 7 14:39:14 GMT 2016
pi@raspberrypi ~ 3}' | sed 's/^1000//'
a02082
pi@raspberrypi ~  ls
aaREADME.txt   DriveSpeed    linpackPiA7SP   LLloops.txt   Source Code
busspeedPiA6   Example Logs  linpackPiSP     memspeedPiA6  Temperature_MHz_Test
busspeedPiA7   java          Linpack.txt     memspeedPiA7  whetstonePiA6
dhrystonePiA6  LanSpeed      Linux Intel     memSpeed.txt  whetstonePiA7
dhrystonePiA7  linpackPiA6   liverloopsPiA6  NEON          whets.txt
Dhry.txt       linpackPiA7   liverloopsPiA7  OpenGL
pi@raspberrypi ~/Raspberry_Pi_Benchmarks $ ./whetstonePiA7

##########################################
Single Precision C Whetstone Benchmark vfpv4 32 Bit, Tue Mar  8 17:16:32 2016

Calibrate
       0.01 Seconds          1   Passes (x 100)
       0.07 Seconds          5   Passes (x 100)
       0.35 Seconds         25   Passes (x 100)
       1.77 Seconds        125   Passes (x 100)
       8.82 Seconds        625   Passes (x 100)

Use 708  passes (x 100)

From File /proc/cpuinfo
processor	: 0
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 76.80
Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xd03
CPU revision	: 4

processor	: 1
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 76.80
Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xd03
CPU revision	: 4

processor	: 2
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 76.80
Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xd03
CPU revision	: 4

processor	: 3
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 76.80
Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer	: 0x41
CPU architecture: 7
CPU vLinux version 4.1.19-v7+ (dc4@dc4-XPS13-9333) (gcc version 4.9.3 (crosstool-NG crosstool-ng-1.22.0-88-g8460611) ) #852 SMP Mon Mar 7 14:39:14 GMT 2016


From File /proc/version
Linux version 4.1.19-v7+ (dc4@dc4-XPS13-9333) (gcc version 4.9.3 (crosstool-NG crosstool-ng-1.22.0-88-g8460611) ) #852 SMP Mon Mar 7 14:39:14 GMT 2016


          Single Precision C/C++ Whetstone Benchmark

Loop content                  Result              MFLOPS      MOPS   Seconds

N1 floating point     -1.12475013732910156       333.681              0.041
N2 floating point     -1.12274742126464844       328.398              0.290
N3 if then else        1.00000000000000000                1790.157    0.041
N4 fixed point        12.00000000000000000                1471.181    0.152
N5 sin,cos etc.        0.49911010265350342                  12.059    4.885
N6 floating point      0.99999982118606567       254.345              1.501
N7 assignments         3.00000000000000000                1188.336    0.110
N8 exp,sqrt etc.       0.75110864639282227                   8.616    3.057

MWIPS                                            702.629             10.076


A new results file, whets.txt,  will have been created in the same
directory as the .EXE files, if one did not already exist.

Type additional information to include in whets.txt - Press Enter