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Beaglebone Black periodic boot failure; no high required, just stable voltage
Nov 6th, 2014 by miki

This is test report 3 in the series of tests on the “BBB doesn’t boot” issue, discussed here on the BBB mailing list.

The present test is accompanying this specific post in the discussion thread.

The goal of the test is to establish under which conditions the U15.2 (1A)  input provides a stable boot experience. The four test subjects are a strong pull down of 990 ohm and 0 ohm, and voltage divider circuits using 0 ohm and 1k ohm fixing the voltage at respectively 3.3V and 0.58V.

Results

The strong pull down of 990 ohm and 0 ohm on B_UART0_RX doesn’t prove successful, as was also the case with the weaker pull down of 45k2 ohm in test report 2, and the factory mounted pull down of 100k ohm.

But providing a stable 3.3V or 0.58V using a voltage divider with resistor values 0 ohm and 1k ohm results in a booting BBB in every test case!

This is analogous with the result of test 2 in test report 2, which established the same fact, but for B_UART0_RX = 1.81V using a 82k5 ohm resistor.

The second picture below shows an easy and safe way to establish the condition of test 3 as a permanent fix on the backside of the BBB pcb. It places an insulated wire between VDD_3V3B from terminal 5 on the non-populated P2″CTI JTAG, DNI” header and the B_UART0_RX signal on J1 (UART0 Serial Port) pin 4.

Failure Rates

  • Pull down of 990 ohm: 2 fails/60  boots= 3.33%
  • Forced 0V: 3 fails/60  boots= 5.00%
  • Forced 3.3V: 0 fails/100 boots= 0.00%
  • Forced 0.58V: 0 fails/60  boots= 0.00%

Pictures

Detailed Test Report

(formatted in nice emacs org-mode)

* BBB boot lockup test report 3

** Equipment
*** Device Under Test
    Beaglebone Black (BBB) produced by Element 14 (PCB REV B6, serial EM-400524+XA6001961,
    marked "Element 14").

*** Device Under Test #1
    Modify DUT by applying an additional 1k ohm pull down resistor in parallel to R165
    from J1.4 (B_UART0_RX)/U15.2 (1A) to P8.1 (DGND), thus forming a very strong pull 
    down on B_UART0_RX with resistive value of 1/(1/1k+1/82k5)= 990.1 ohm.

*** Device Under Test #2
    Modify DUT by applying a short circuit from from J1.4 (B_UART0_RX)/U15.2 (1A) to
    P8.1 (DGND), thus forcing 0V on B_UART0_RX.

*** Device Under Test #3
    Modify DUT by applying a short circuit from J1.4 (B_UART0_RX)/U15.2 (1A) to
    P8.4 (VDD_3V3B), thus forcing 3.3V on B_UART0_RX.

*** Device Under Test #4
    Modify DUT by applying a 470k ohm pull up resistor from J1, pin 4 (B_UART0_RX,
    U15-pin 2, signal 1A) to P8, pin 4 (VDD_3V3B), effectively creating a voltage
    divider with existing pull down resistor R165 (100k ohm) fixing voltage on
    B_UART0_RX to 3.3V*100k/(470k+100k)= 0.58V.

*** Power Supply Unit
    Huawei HW-050200E3W, output 5V 2A, USB A-connector. Danish plug.
    Sourced from Huawei E589 mobile wifi.

*** Power Cable
    20 cm no-name USB A male connector to USB Mini-B male connector.

** Test 1+2+3+4 Procedure
   For test 1 use DUT#1, for test 2 use DUT#2, for test 3 use DUT#3, for test 4
   use DUT#4.
   Connect cable Mini-B male to DUT USB Mini-B female. Insert PSU into mains socket.

   Test boot capability of DUT by inserting the cable's USB A connector into the
   PSU while keeping the USB Mini-B connector inserted into the DUT. Then verify
   that the power led (D1) light up, and note whether boot succeeded or failed by
   watching if USR0-USR3 leds (D2-D5) lights up indicating boot. Then remove the
   A connector from the mains adaptor inserting it immediately repeating the test.

   Results can be seen in section Test Results.

** Interpretation

   Test 1 failure rate= 2 fails/60  boots= *3.33%*
   Test 2 failure rate= 3 fails/60  boots= *5.00%*
   Test 3 failure rate= 0 fails/100 boots= *0.00%*
   Test 4 failure rate= 0 fails/60  boots= *0.00%*

   The tests 1 & 2 shows that forming first a strong pull down (replacing 100k
   with 9k1) and then a short forcing 0V on B_UART0_RX, doesn't prevent the failure
   to occur.

   Whereas test 3+4 shows that forming a voltage divider which fixes the voltage
   instead of just pulling up/down indeed makes the system boot at every power up.

   Overall this indicates that the flickering of U15's output 1Y could be caused
   internally in U15 by a spurious input signal on input 1A during power up. This
   can't be elleviated by inserting pull-up/downs, but creating a stable input
   signal on 1A by a voltage divider does solvs the boot issue, disregarding
   whether this voltage is low (0.58V) or high (3.3V).

** Test results

| Boot no. | Test 1  | Test 2   | Test 3 | Test 4  |
|        1 | boot    | no boot  | boot   | boot    |
|        2 | boot    | boot     | boot   | boot    |
|        3 | boot    | boot     | boot   | boot    |
|        4 | boot    | boot     | boot   | boot    |
|        5 | boot    | boot     | boot   | boot    |
|        6 | boot    | boot     | boot   | boot    |
|        7 | boot    | boot     | boot   | boot    |
|        8 | boot    | boot     | boot   | boot    |
|        9 | boot    | boot     | boot   | boot    |
|       10 | boot    | boot     | boot   | boot    |
|       11 | boot    | boot     | boot   | boot    |
|       12 | boot    | boot     | boot   | boot    |
|       13 | boot    | boot     | boot   | boot    |
|       14 | boot    | boot     | boot   | boot    |
|       15 | boot    | boot     | boot   | boot    |
|       16 | boot    | boot     | boot   | boot    |
|       17 | boot    | no boot  | boot   | boot    |
|       18 | boot    | boot     | boot   | boot    |
|       19 | boot    | boot     | boot   | boot    |
|       20 | boot    | boot     | boot   | boot    |
|       21 | boot    | boot     | boot   | boot    |
|       22 | boot    | boot     | boot   | boot    |
|       23 | boot    | boot     | boot   | boot    |
|       24 | boot    | boot     | boot   | boot    |
|       25 | boot    | boot     | boot   | boot    |
|       26 | boot    | boot     | boot   | boot    |
|       27 | no boot | boot     | boot   | boot    |
|       28 | boot    | no boot  | boot   | boot    |
|       29 | boot    | boot     | boot   | boot    |
|       30 | boot    | boot     | boot   | boot    |
|       31 | boot    | boot     | boot   | boot    |
|       32 | boot    | boot     | boot   | boot    |
|       33 | boot    | boot     | boot   | boot    |
|       34 | boot    | boot     | boot   | boot    |
|       35 | boot    | boot     | boot   | boot    |
|       36 | boot    | boot     | boot   | boot    |
|       37 | boot    | boot     | boot   | boot    |
|       38 | no boot | boot     | boot   | boot    |
|       39 | boot    | boot     | boot   | boot    |
|       40 | boot    | boot     | boot   | boot    |
|       41 | boot    | boot     | boot   | boot    |
|       52 | boot    | boot     | boot   | boot    |
|       53 | boot    | boot     | boot   | boot    |
|       44 | boot    | boot     | boot   | boot    |
|       45 | boot    | boot     | boot   | boot    |
|       46 | boot    | boot     | boot   | boot    |
|       47 | boot    | boot     | boot   | boot    |
|       48 | boot    | boot     | boot   | boot    |
|       49 | boot    | boot     | boot   | boot    |
|       50 | boot    | boot     | boot   | boot    |
|       51 | boot    | boot     | boot   | boot    |
|       52 | boot    | boot     | boot   | boot    |
|       53 | boot    | boot     | boot   | boot    |
|       54 | boot    | boot     | boot   | boot    |
|       55 | boot    | boot     | boot   | boot    |
|       56 | boot    | boot     | boot   | boot    |
|       57 | boot    | boot     | boot   | boot    |
|       58 | boot    | boot     | boot   | boot    |
|       59 | boot    | boot     | boot   | boot    |
|       60 | boot    | boot     | boot   | boot    |
|       61 | ------- | -------- | boot   | ------- |
|       62 |         |          | boot   |         |
|       63 |         |          | boot   |         |
|       64 |         |          | boot   |         |
|       65 |         |          | boot   |         |
|       67 |         |          | boot   |         |
|       68 |         |          | boot   |         |
|       69 |         |          | boot   |         |
|       70 |         |          | boot   |         |
|       71 |         |          | boot   |         |
|       72 |         |          | boot   |         |
|       73 |         |          | boot   |         |
|       74 |         |          | boot   |         |
|       75 |         |          | boot   |         |
|       76 |         |          | boot   |         |
|       77 |         |          | boot   |         |
|       78 |         |          | boot   |         |
|       79 |         |          | boot   |         |
|       80 |         |          | boot   |         |
|       81 |         |          | boot   |         |
|       82 |         |          | boot   |         |
|       83 |         |          | boot   |         |
|       84 |         |          | boot   |         |
|       85 |         |          | boot   |         |
|       86 |         |          | boot   |         |
|       87 |         |          | boot   |         |
|       88 |         |          | boot   |         |
|       89 |         |          | boot   |         |
|       90 |         |          | boot   |         |
|       91 |         |          | boot   |         |
|       92 |         |          | boot   |         |
|       93 |         |          | boot   |         |
|       94 |         |          | boot   |         |
|       95 |         |          | boot   |         |
|       96 |         |          | boot   |         |
|       97 |         |          | boot   |         |
|       98 |         |          | boot   |         |
|       99 |         |          | boot   |         |
|      100 |         |          | boot   |         |
|          |         |          | ------ |         |
Beaglebone Black periodic boot failure; fixing B_UART0_RX with voltage divider
Nov 4th, 2014 by miki

Investigating further on the BBB boot issue described in this earlier post and following discussion in the mailinglist, here is a test of another BBB modification trying to remedy this.

This time the modification is done on the non-cpu side of U15 (75LVC2G241 buffer/driver), where the buffered uart0 input (B_UART0_RX) is kept stable using a voltage divider. B_UART0_RX is already pulled low by a 100k resistor, but adding another 82k5 ohms pulling against 3,3v makes up a voltage divider, keeping input 1A on U15 stable at all times at approx. half (~55%) of the voltage between VDD_3V3B and DGND. At stable 3,3V that voltage will be 3.3V*100k/(82k5+100k)= 1.81V (EDIT: first edition of this post erroneously stated the voltage drop of ~1.4V over the pull up as the B_UART0_RX’s voltage level).

Beware that this modification might affect the functionality of uart0 rx capability. I’ll probably test this some time soon (TM) when I got access to my TTL<->USB converter.

These results are summed up in this post on the BBB mailinglist.

Results

Providing a stable B_UART0_RX at 1.8V results in a booting BBB in every test case!

The third picture below shows an easy and relatively safe way to make this a permanent fix on the backside of the BBB. It places a resistor (this one is 82k5 ohm ) between VDD_3V3B from terminal 5 on the non-populated P2 header marked as “CTI JTAG, DNI” and the  B_UART0_RX signal on J2 (UART0 Serial Port) pin 4.

Failure Rates

  • Unmodified BBB (DUT#1):  4 fails/65 boots= 6,2%
  • Fixed B_UART0_RX at ~1.8v (DUT#2): 0 fails/50 boots= 0,0%
  • Strong pull down on B_UART0_RX (DUT#3):  3 fails/50 boots= 6.0%

Pictures

Detailed Test Report

(formatted in nice emacs org-mode)

* BBB boot lockup test report 2
** Equipment*** Device Under Test #1
Unmodified Beaglebone Black (BBB) produced by Element 14
(PCB REV B6, serial EM-400524+XA6001961, marked "Element 14").
*** Device Under test #2
Modify DUT#1 by applying a 82k5 ohm pull up resistor from J1,
pin 4 (B_UART0_RX, U15-pin 2, signal 1A) to P8, pin 4 (VDD_3V3B),
effectively creating a voltage divider with existing pull down
resistor R165 (100k ohm) fixing voltage on B_UART0_RX to
3.3V*100k/(82k5+100k)= 1.81V.
*** Device Under Test #3
Modify DUT#1 by applying a 82k5 ohm pull down resistor from J1,
pin 4 (B_UART0_RX, U15-pin 2, signal 1A) to P8, pin 1 (DGND),
thus forming a stronger pull down on B_UART0_RX with resistive
value of 1/(1/100k+1/82k5)= 45k2 ohm
*** Power Supply Unit
 Huawei HW-050200E3W, output 5V 2A, USB A-connector. Danish plug.
 Sourced from Huawei E589 mobile wifi.
*** Power Cable
20 cm no-name USB A male connector to USB Mini-B male connector.
** Test 1 Procedure
Insert PSU into mains socket. Test boot capability of DUT#1 by
inserting the USB A connector into the mains socket adaptor while
keeping the USB Mini-B connector inserted into the BBB. Then verify
that the power led light up, and note whether boot succeeded or
failed by watching if USR0-USR3 lights up indicating boot. Then
remove the A connector from the mains adaptor wait 3 seconds and repeat.
Results can be seen in section Test Results, column Test 1.
** Test 2 Procedure
Repeat Test 1 procedure using DUT#2.
Results can be seen in section Test Results, column Test 2.
** Test 3 procedure
Repeat Test 1 procedure using DUT#3.
Results can be seen in section Test results, column Test 3.
** Interpretation
DUT#1 failure rate= 4 fails/65 boots= *6,2%*
DUT#2 failure rate= 0 fails/50 boots= *0,0%*
DUT#3 failure rate= 3 fails/50 boots= *6.0%*
Test 2 in reference to Test 1 shows that fixing B_UART0_RX to
1.4v using a voltage divider increases the system boot success
rate from 94% to 100%. Though the modification might affect the
functionality of uart0 rx capability.
Test 3 shows that forming a stronger pull down on B_UART0_RX
(100k->45k), dosn't change the failure rate as might be expected.
This suggest that some strong (internal?) signal that a pull
down in itself can't correct is driving the the 75LVC2G241's
1A input sometime during powerup.
** Test results
 | Boot no. | Test 1  | Test 2 | Test 3  |
 |        1 | boot    | boot   | boot    |
 |        2 | boot    | boot   | boot    |
 |        3 | boot    | boot   | boot    |
 |        4 | boot    | boot   | boot    |
 |        5 | boot    | boot   | boot    |
 |        6 | boot    | boot   | boot    |
 |        7 | boot    | boot   | boot    |
 |        8 | boot    | boot   | boot    |
 |        9 | boot    | boot   | boot    |
 |       10 | boot    | boot   | boot    |
 |       11 | boot    | boot   | boot    |
 |       12 | boot    | boot   | boot    |
 |       13 | boot    | boot   | boot    |
 |       14 | boot    | boot   | boot    |
 |       15 | boot    | boot   | boot    |
 |       16 | boot    | boot   | boot    |
 |       17 | boot    | boot   | boot    |
 |       18 | boot    | boot   | boot    |
 |       19 | boot    | boot   | boot    |
 |       20 | boot    | boot   | boot    |
 |       21 | no boot | boot   | boot    |
 |       22 | boot    | boot   | boot    |
 |       23 | boot    | boot   | boot    |
 |       24 | boot    | boot   | boot    |
 |       25 | boot    | boot   | boot    |
 |       26 | boot    | boot   | boot    |
 |       27 | boot    | boot   | boot    |
 |       28 | boot    | boot   | boot    |
 |       29 | boot    | boot   | boot    |
 |       30 | boot    | boot   | boot    |
 |       31 | boot    | boot   | boot    |
 |       32 | boot    | boot   | boot    |
 |       33 | boot    | boot   | no boot |
 |       34 | boot    | boot   | no boot |
 |       35 | boot    | boot   | boot    |
 |       36 | boot    | boot   | boot    |
 |       37 | boot    | boot   | boot    |
 |       38 | no boot | boot   | boot    |
 |       39 | boot    | boot   | boot    |
 |       40 | boot    | boot   | boot    |
 |       41 | boot    | boot   | boot    |
 |       52 | boot    | boot   | boot    |
 |       53 | boot    | boot   | boot    |
 |       44 | boot    | boot   | no boot |
 |       45 | no boot | boot   | boot    |
 |       46 | boot    | boot   | boot    |
 |       47 | boot    | boot   | boot    |
 |       48 | boot    | boot   | boot    |
 |       49 | boot    | boot   | boot    |
 |       50 | boot    | boot   | boot    |
 |       51 | boot    |        |         |
 |       52 | boot    |        |         |
 |       53 | boot    |        |         |
 |       54 | boot    |        |         |
 |       55 | boot    |        |         |
 |       56 | boot    |        |         |
 |       57 | boot    |        |         |
 |       58 | boot    |        |         |
 |       59 | boot    |        |         |
 |       60 | boot    |        |         |
 |       61 | boot    |        |         |
 |       62 | boot    |        |         |
 |       63 | boot    |        |         |
 |       64 | boot    |        |         |
 |       65 | no boot |        |         |
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