iMX7 SPI Chip select is active low after M4 startup till first use

Technical Support
, ,
1

SPI working. However by default the chip select remains active low and boot till 1st use of port. Problem if 2 chip selects and both are active low.

Two questions:

  1. SPI is mostly configured correctly since it works. How to default to inactive high.

  2. Assume after power up, a pin does not yet know it’s SPI or GPIO and would be Hi-impedance. Is the boot loader forcing the CS low?

How early can a pin be configured? Power-up Hi-Z?
Inside the boot loader or once program runs on M4?

thanks,
Robert

2

Dear @bobpbbd104

  1. I haven’t used SPI with two chip selects myself. I recommend you read the SPI documentation in the i.MX7 reference manual to learn how to configure the second SPI chip-select inactive. If the SPI controller does not support it (it might be a bug in the chip hardware?) a simple workaround would be to issue a dummy transfer as part of the initialization sequence.
  2. The power-up state of the pins is hard-wired in the i.MX7 chip and therefore cannot be configuerd. The reset state is documented in the i.MX7 reference manual. If the signal’s reset state is High-Z, you can add a pull-up resistor to force it high.
    The bootloader’s configuration options depend on the actual bootloader you are using.

Regards, Andy