Werner's Miscellanea
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| 1 | M1pre-rc4 vs. shorted USB |
| 2 | ========================= |
| 3 | |
| 4 | These are the results of supplying an M1 equipped with a |
| 5 | current-limiting power switch from a lab supply and shorting or |
| 6 | (over)loading one USB port. Note that this test involved only |
| 7 | resistive loads. |
| 8 | |
| 9 | Source Input J21/J3 Boot Short USB Load USB (2 Ohm) |
| 10 | ------- --------------- --------------- ------- --------------- --------------- |
| 11 | 4.50 - - No - - |
| 12 | 4.60 4.41/4.46/4.50 4.03/4.20/4.33 Unstbl. Reset 4.04/4.09/4.33 |
| 13 | 4.70 4.51/4.57/4.60 4.15/4.31/4.43 Unstbl. Reset 4.16/4.22/4.43 |
| 14 | 4.80 4.61/4.66/4.70 4.22/4.40/4.52 Yes Reset 4.25/4.32/4.53 |
| 15 | 4.90 4.71/4.76/4.80 4.29/4.47/4.60 Yes Reset 4.39/4.46/4.62 |
| 16 | 5.00 * 4.81/4.86/4.90 4.47/4.62/4.72 Yes Reset [1,2] 4.48/4.55/4.72 |
| 17 | 5.10 - - Yes Reset - [3] |
| 18 | 5.20 - - Yes Reset - |
| 19 | 5.30 5.10/5.16/5.19 4.61/4.86/4.99 Yes Unstbl. - |
| 20 | 5.40 - 4.85/5.01/5.10 Yes 4.89/5.01/5.11 [4] - |
| 21 | |
| 22 | * Voltage at source: 4.99/5.01/5.01 V |
| 23 | |
| 24 | - not measure either because measurement was not applicable or |
| 25 | because the result would have been of limited interest. |
| 26 | |
| 27 | All voltage measurements min/avg/max, over 3000 samples. Flickernose |
| 28 | was rendering "The Tunnel" at the time. The M1pre-rc4 was running |
| 29 | the vanilla 2011-07-13 installation. |
| 30 | |
| 31 | "Source" is the nominal supply voltage, from a Leaptronix mPP-3040D, |
| 32 | with current limit set to 3.0 A. |
| 33 | |
| 34 | "Input" is the voltage measured on the supply cables near the M1's |
| 35 | DC input. |
| 36 | |
| 37 | "J21/J3" is the voltage on the internal 5 V rail measured across |
| 38 | J21.1 and J3.14, with a Fluke 8845A with averaging set to 1 PLC. |
| 39 | [5] shows the measurement configuration. |
| 40 | |
| 41 | "Boot" indicates whether the M1 can boot out of standby with the |
| 42 | respective voltage and current limit. If only unstable operation |
| 43 | was achieved, M1 only sometimes booted or reset after running for |
| 44 | some minutes. |
| 45 | |
| 46 | "Short USB" indicates what happens if one USB port is shorted |
| 47 | through labsw. In all most, the voltage drop on the 5 V rail was |
| 48 | sufficiently large to cause a reset. [1] and [2] show the internal |
| 49 | 5 V rail in channel 1, and the external VBUS on channel 2. Note |
| 50 | that the resistive probes used have a few percent of linear error. |
| 51 | [6] shows the external setup on the USB port. |
| 52 | |
| 53 | If setting a supply voltage well above the nominal 5.0 V, even |
| 54 | shorts on USB can be survived. At 5.30 V and 5.40 V, resets still |
| 55 | occurred frequently. [4] shows the 5 V rail (barely) escaping a |
| 56 | reset. |
| 57 | |
| 58 | "Load USB (2 Ohm)" repeats the same experiment with a 2 Ohm series |
| 59 | resistor added. [3] shows the response. Occasional resets occurred |
| 60 | at nominal voltages of 4.80 V or below. |
| 61 | |
| 62 | [1] usb-short-100us.png |
| 63 | [2] usb-short-10us.png |
| 64 | [3] usb-2R-200us.png |
| 65 | [4] usb-short-5V4.png |
| 66 | [5] tap-j21j3.jpg |
| 67 | [6] tap-usb.jpg |
| 68 |
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