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