-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi Chu.
On 2014-11-05 11:47, Mikkel Kirkgaard Nielsen wrote: > As my modification also solves the issue, your assumption about > your fix (a high level at J4.1/B_UART0_RX (U15.2/1A)) is not true. Sorry, J1.4 is the correct pin. I've now done tests with a stronger pulldown (1k in parallel with R165= 990 ohm) and a short directly to DGND/VDD_3V3B (I'll post details later, find them at http://www.mikini.dk/index.php/category/beaglebone-black). These tests confirm that B_UART0_RX can't be pulled down/up, to prevent the failure to occur. But forming a stable voltage on the input using a voltage divider (also using 0 ohm= short circuit!) does solve the problem. That is; whether we form a stable 0.58V or a stable 3.3V on B_UART0_RX the system will always boot. Does anybody have definite confirmation (by scope measurements) that U15.6 (1Y) really is flickering during early power? It would be exiting to do some experiments showing how it is affected by the U15.3 (1A) input. I think that is the core of this issue. >> We removed the R165 which is the pull down resistor on the >> UART0_RX line. The UART0_RX is around 1.4V and sometimes >> floating. We also checked the device tree. The internal pull up >> of the UART0_RX is turned on. [UART0_RX on 1.4V or floating] > Peculiar, as it should never float. I haven't been able to replicate that measurement. I got 3V3 on UART0_RX (the one without B_, on the cpu side), except in early power up. I see the voltage flickering shortly just after power is applied, and in the same instance that kernel is loaded (USR0-USR3 leds starts lighting up) there also some activity. Are you sure that you actually did measure on U15.6? It isn't easy to place the probes right on those small pads. >> We do not know why the UART0_RX is not getting 3.3V, can you >> please check the voltage on both UART0_TX and UART0_RX when U15 >> is removed? > I'll definitely look into this tomorrow. Including taking this > measurement. Here they are, I see nothing unexpected here when things are static. I also checked the U15 supply, which seems to be ok. * BBB measurements on terminals of removed U15 ** Device Under Test: Modified Beaglebone Black produced by CircuitCo (PCB REV B6, serial 007142901445, marked "beaglebone"+ beagle logo and "beagleboard.org"). Modified by removing U15 (uart0 buffer chip: SN74LVC2G241) and its decoupling capacitor C155. ** Equipment *** Multimeter Brymen Elma BM515CF MOBILE LOGGER, MFG.#: 063391676. *** 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. ** Procedure Apply power to BBB through USB Mini-B connector. Use multimeter to measure voltage levels on exposed U15 terminals and related supply lines to check possible supply voltage drop. COM probe fixed at DGND on decoupling capacitor (terminal C155.DGND farthest from PCB edge). ** Measurements C155.VDD_3V3B: 3.352V (terminal nearest to PCB edge) U15.1: _1OE = 0V U15.2: 1A = 0V U15.3: 2Y = floating (flickering +-0.000,50V) U15.4: GND = 0V U15.5: 2A = UART0_RX = 3.335V U15.6: 1Y = UART0_TX = 3.195V U15.7: 2OE = 3.352V U15.8: VCC = 3.352V J1.1 = DGND = 0.000,02 V P2.20 = GND5 = 0.000,02 V FB4.1 = VDD_3V3B = 3.351 V > Regads, Even more regads, - -- Mikkel ,= ,-_-. =. ((_/)o o(\_)) `-'(. .)`-' \_/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJUW47fAAoJEJ2luFWzaTSanH0H+gKv5DcQ/9NeX0vuf+9eIE3r 6mNho8sKbpWtx6uGcLRZzxEBLbU0NWnq/ePzhCzbWq7c/nEyXlYwtoa7hagJl7VT OGaqjxxvt3Ti/iVTLp1rtiCm97Uyi0DzOKxuM8SwFTQDXTjWdmp/2ArApJqETZUD PkpBABtfvFFWenks5rEpUYvQlI+a3SGL6nBHDmYdfD1bLExlM3ceKZ/rlCiIuHQa 8+Gj8BnoSfXO7FYk/3zUX13bBxEne2tdFgNtkOsqZK8/ut8G72jsrQwi2HmA1i1j 77CcoyTKUUeVwThcqx544pWDCvYx4FuAJz7dqIuTp3eNjHDN0JHcjNdemaL6O1M= =LasS -----END PGP SIGNATURE----- -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
