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
-
-
B_UART0_RX pull up/down test mockup.
-
-
Permanently fixing B_UART0_RX (J1.4) to VDD_3V3B (P2.5).
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 | |
| | | | ------ | |
