No boot – Wrong RTC Configuration?

[jp9830]

I’m troubleshooting a new board (OSD3358 C-SiP) that has not yet successfully booted.
The SYSBOOT configuration matches the Octavo CSiP-RED EVM board (and Beaglebone Black), which has a default order of MMC1,MM0,UART0,USB0, with a jumper to allow reording to SPI0, MMC0, USB0, UART0.

When I apply 5V to the C-SiP, I don’t see any uboot messages on UART0. With a scope, I don’t see any activity from the uSD card (probing the CLK line of the uSD). I can change the boot config jumper and don’t see any activity on SPI0 CLK either when I do that. I’ve double checked my PCB layout for the uSD card and it seems correct.

I’m using the same test points used on the C-SiP EVM (VDD_MPU, VDDS_DDR, VDDS_PLL, VDD_CORE) and those voltages all match what the datasheet specifies. I also can see a 24MHz clock active on OSC0_TP (pin M6). I have an LED on SYS_VDD1_3P3V which lights properly and shows that voltage rail (VDD_3V3B) is correct.

I know I made one mistake in my layout. I am not using the RTC subsystem, so I intended to disable it. Section 7.5.4 “Minimum RTC Power” had the connections listed but I neglected to connect VDDS_RTC (pin M13) and VDDS (M14) to SYS_RTC_1P8V. I attached the relevant section of my schematic that has my error.

My question is- does my schematic mistake completely describe this fail-to-boot issue, or is it likely that there is another issue occurring? I hate to respin this board, only to have the same problem remain. Since I’m seeing 3.3V all the other voltage rails, and the active OSC0– it seems like the PMIC is working, so it made me question whether this is truly the cause of the boot failure.

Attachments:

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   Screenshot_20200320_153728.png
   

[Neeraj Dantu]

JP,

VDDS_RTC is the power supply for the RTC subsystem. This power rail needs to be powered by a 1.8V power rail whether RTC subsystem is to be used or not. So, not connecting VDDS, VDDS_RTC to SYS_RTC_1P8V is most likely the cause for the board not booting. See section 6 (Power and Clocking) of AM335x datasheet for more information on the boot process and VDDS_RTC’s role: http://www.ti.com/lit/ds/symlink/am3358.pdf

We recommend using the same circuit configuration as the SM-RED board for RTC subsystem, as it is the easiest to bring up.

Please go through the following resources so you can catch everything that needs to be changed for the next revision:

1. Schematic checklist: https://octavosystems.com/app_notes/osd335x-schematic-checklist-am335x/

2. OSD335x C-SiP reference design: https://octavosystems.com/docs/osd3358-sm-red-c-sip-schematics-pdf/

Best,

Neeraj

[jp9830]

Thanks Neeraj,

I was hopeful that because the other rails had come up successfully (VDD_MPU, VDD_CORE, VDDS_DDR) and the AM335x datasheet Figure 6-6 (Power Supply Sequencing) only shows those rails coming up *after* VDDS_RTC, that perhaps this wasn’t the source of the problem.
Regardless, it’s a mistake I need to correct.

Appreciate the prompt support!

[Author]

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