CODEWITHSUNDEEP
driverbeagleboneblackgpiospidevice-tree
SergeyM
SergeyM

Reputation: 175

SPI without CS pins configured (BeagleBone Black)

I don't need to use the "stock" CS signals for SPI in BeagleBone Black. Can I just omit their configuration in DTBO to save a couple of GPIOs? In other words, (1) will SPI work properly? (2) may it cause a GPIO conflict? Here is a DTS fragment example for SPI1:

....
fragment@0 {
    target = <&am33xx_pinmux>;
    __overlay__ {
        /* default state has all gpios released and mode set to uart1 */
        bb_spi1_pins: pinmux_bb_spi1_pins {
            pinctrl-single,pins = <
                0x190 0x13  /* mcasp0_aclkx.spi1_sclk,  OUTPUT_PULLUP | MODE3 */
                0x194 0x33  /* mcasp0_fsx.spi1_d0,      INPUT_PULLUP  | MODE3 */
                0x198 0x13  /* mcasp0_axr0.spi1_d1,     OUTPUT_PULLUP | MODE3 */
            >;
        };
    };
};
....

Which kernel driver should I look into to verify? It looks that spidev.c is too high-level.

Thanks for directions!

Upvotes: 1

Views: 734

Answers (2)

mahegaik
mahegaik

Reputation: 11

I just did that for one of the home projects i was working with, connected CS simply to ground, I could do this primarily because i do not have more than one slave on my SPI bus.

Upvotes: 0

SergeyM
SergeyM

Reputation: 175

Since the pin can be unconnected, so it doesn't matter which pin is used if the pinmux is configured to use it for a different purpose. Thus I consider this solved – perfectly works here.

  fragment@0 {
  target = <&am33xx_pinmux>;
    __overlay__ {
    . . . .
        bb_spi1_pins: pinmux_bb_spi1_pins {
            pinctrl-single,pins = <
                BONE_P9_31 (PIN_INPUT  | MUX_MODE3) // spi1_sclk
                BONE_P9_29 (PIN_INPUT  | MUX_MODE3) // spi1_d0 (miso)
                BONE_P9_30 (PIN_OUTPUT | MUX_MODE3) // spi1_d1 (mosi)
                BONE_P9_28 (PIN_OUTPUT | MUX_MODE7) // spi1_cs0
                // for spi1_cs0 it has to be MUX_MODE3, but since we want
                // to use it as a GPIO we set to MUX_MODE7, which
                // corresponds to GPIO3_14
            >;
        };
    . . . .
    }
  }

The code snippet above contains macros from Robert Nelson's overlays collection and build suite.

Upvotes: 1

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