Need McSPI4_SOMI high when nRESET goes high

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1

Hi,

I have a custom board attached to the expansion connector and a number of chips on the board with their RESET lines connected to nRESET. One particular chip has an SPI interface that I have connected to McSPI4. To configure the chip to use SPI, I need to drive the McSPI4_SOMI line high before the nRESET line goes high.

I have my pin MUX in U-Boot set to:
MUX_VAL(CP(MCBSP1_DR), (IEN | PTU | EN | M1))

And on the board I have a 10K resistor from the line to 1.8V.

However, when scoping out the values, I see the line go to about 400mV about 8ms before the nRESET line goes high and stays there. Eventually the line does go full high.

Is the pin actually driving a low output at nRESET time? How do I drive this line high when I need to?

-Stevo Brock

2

Steve,

the best solution for you is to implement a standalone reset for your
device using something like a NCP303. you can adjust the reset time
for your specific devices. we've had to do that on several omap3
projects.

thanks
Dave

3

Hi Dave,

Thanks for the response. I ended up cutting the Reset trace and wiring it to GPIO 162 and triggering it myself.

-Stevo

4

Hi Stevo,

Thanks for the response. I ended up cutting the Reset trace and wiring
it to GPIO 162 and triggering it myself.

Just for a complete reference on this for the future. The McSPI4_SOMI can't
be made to start HIGH when nReset is released regardless what you do. The
Reset state of this ball is internally pulled LOW with a drive strength of
~100uA (which can be seen in the OMAP Data Manual - omap3530.pdf), which is
why you get the intermediate voltage of 400mV for 8ms (due to your external
pull-up resistor :slight_smile: until you get to your pin-muxing code in U-boot.

Glad that you solved your problem in another way though :slight_smile:
  Søren

5

Thanks for the detailed info.

-Stevo