Custom BB cape affecting kernel boot

Hi all,

I have a custom cape made for BB black, and when I have the cape plugged in to the BB and turning my BB on, it seems to stop the kernel from booting properly. I have Linux angstrom installed. Im attaching the kernel trace here so that everyone knows what happens (I got this using FTDI to USB connection, that we know what process being performed during boot up). Can anyone help in identifying the cause of this?


BB cape trace.txt (6.49 KB)

How are you powering up your board?
Is booting fine without cape?

Hi there,

Im using the supplied power adapter for powering up, and yes booting is fine without cape.


Oh another thing is, if I plug the cape after the BB has finished booting, the BB is still operating normally.

I haven’t looked at your schematic, but if you are pulling some signals certain ways, you might be adjusting the boot mode.


The BB itself has its HDMI disabled, thus I assume there’s no conflicting pins when using the cape. The cape itself utilizes P8_01, P8_02, P8_27 until P8_34 and P9_01, P9_02, and P9_21 until P9_28. The cape gets its power not from the power adapter from the BB but from another power supply, thus it doesn’t absorb power from the BB at all. But even with having the cape unpowered, the BB still cant finish booting the kernel. If it somehow adjusting boot mode, which pin number that (if any being used by the cape) is being used by the BB for kernel booting?


All of the LCD/HDMI pins are used to set the boot mode and cannot be
driven until after reset goes high unless you are intentionally trying
to change the boot mode.

This is covered in the SRM, see section 8.1.1 "LCD Pins":

* These pins are also the SYSBOOT pins. DO NOT drive them before the
SYS_RESETN signal goes high. If you do, the board may not boot because
you would be changing the boot order of the processor.

More details are available in 8.3.1 "Boot Pins" and on the schematic.

Hi there,

Thanks for the answer, Charles. Another question if you dont mind, you mentioned that All of the lcd/hdmi pins are used, so does it mean that P8_27-P8_30 are also used for boot process? I didn’t see those pins being included as the boot pins in the BB SRM docs.


All of the LCD_DATA[] pins, as shown in the SRM And the schematic.