MISO pin internal pullup in SPI configuration

Hi Satoru,

On MAX32xxx devices, the weak and strong pull-ups are controlled within the GPIO pad block. Many of the SPI initialization helpers internally invoke MXC_GPIO_Config() for their pin mapping, which typically resets the pad configuration to its default state (i.e., no pull-up or pull-down). As a result, if a pull-up is configured prior to calling MXC_SPI_Init(), the driver will overwrite those pad settings.

To address this, please proceed as follows:

• Retain the MXC_SPI_Init() call as is.

• Immediately after invoking it, apply a one-pin override for MISO in its SPI alternate function. Specifically, use MXC_GPIO_FUNC_ALT1 for SPI1_MISO on P0.22.

// 1) Bring up SPI first
MXC_SPI_Init(MXC_SPI0, 1, 0, 0, 0, /*... your args ...*/);

// 2) Re-apply pad config for MISO in its ALT function
mxc_gpio_cfg_t miso = {
    .port   = MXC_GPIO0,
    .mask   = MXC_GPIO_PIN_22,          // P0.22 = SPI1 MISO pin
    .func   = MXC_GPIO_FUNC_ALT1,       // the exact ALT for SPI1 MISO on P0.22
    .pad    = MXC_GPIO_PAD_PULL_UP,     // weak pull-up enabled
    .vssel  = MXC_GPIO_VSSEL_VDDIOH,    // if that pad is on the 3.3V bank
    .drvstr = MXC_GPIO_DRVSTR_0,
};
MXC_GPIO_Config(&miso);

This approach remains robust even if you re-initialize SPI at a later point—simply re-apply the one-line override after each initialization.

Kind regards,

Haluk

Hi Haluk,

Thank you for your advice. My MISO pin pullup worked as you suggested.

Satoru

Hi Haluk,

Thank you for your advice. My MISO pin pullup worked as you suggested.

Satoru