Hi All
This example shows how to configure a peripheral pin with help if the _CONFIG_PERIPHERAL() or _CONFIG_PERIPHERAL_LOOPBACK() macros.
As an example I will configure LPSPI3_SCK function on the pin referenced as GPIO_AD_B1_15 (assuming an i.MX RT 106x)
This is the code:
IOMUXC_LPSPI3_SCK_SELECT_INPUT = IOMUXC_LPSPI3_SCK_SELECT_INPUT_GPIO_AD_B1_15_ALT2;
_CONFIG_PERIPHERAL_LOOPBACK(GPIO_AD_B1_15, LPSPI3_SCK, (IOMUXC_SW_PAD_CTL_PAD_PKE | IOMUXC_SW_PAD_CTL_PAD_SPEED_MEDIUM | IOMUXC_SW_PAD_CTL_PAD_DSE_6));
and this is how one arrives at it:
1. One needs to know which GPIO reference (PAD) it is on -> GPIO_AD_B1_15 in this case
2. One searches for this in iMX.h until one finds the list of mux options belonging to it
#define GPIO_AD_B1_15_FLEXSPIA_SS0_B (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT0)
#define GPIO_AD_B1_15_ACMP_OUT03 (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT1)
#define GPIO_AD_B1_15_LPSPI3_SCK (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT2)
#define GPIO_AD_B1_15_SAI1_TX_SYNC (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT3)
#define GPIO_AD_B1_15_CSI_DATA02 (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT4)
#define GPIO_AD_B1_15_GPIO1_IO31 (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT5)
#define GPIO_AD_B1_15_USDHC2_DATA7 (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT6)
#define GPIO_AD_B1_15_KPP_COL00 (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT7)
#if defined iMX_RT106X
#define GPIO_AD_B1_15_ENET2_1588_EVENT3_IN (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT8)
#define GPIO_AD_B1_15_FLEXIO3_FLEXIO15 (IOMUXC_SW_MUX_CTL_PAD_MUX_MODE_ALT9)
#endif
3. One take the full mux name (GPIO_AD_B1_15_LPSPI3_SCK) and insert it into the macro, with a comma separating the GPIO reference and the peripheral mux reference belonging to that GPIO:
_CONFIG_PERIPHERAL_LOOPBACK(GPIO_AD_B1_15, LPSPI3_SCK, (IOMUXC_SW_PAD_CTL_PAD_PKE | IOMUXC_SW_PAD_CTL_PAD_SPEED_MEDIUM | IOMUXC_SW_PAD_CTL_PAD_DSE_6));
This can't be done wrong since it will not compile if incorrect GPIOs aad peripherals are attempted.
The characteristics (last parameter) can be modified to control drive strength and slew rate, etc.
4. Note that either _CONFIG_PERIPHERAL() or _CONFIG_PERIPHERAL_LOOPBACK() is used.
The first is used in most cases but the _CONFIG_PERIPHERAL_LOOPBACK() one is needed for some signals that are generated to be driven onto the pin and also need to be looped back internally to be driven to the peripheral itself. In the case of the LPSPI master operation this MUST be used for the CLK otherwise the clock will be generated but not be connected internally, meaning it won't work completely.
5. Some peripheral pins need an additional sub-muxing setting since they can be located on multiple pins.
IOMUXC_LPSPI3_SCK_SELECT_INPUT = IOMUXC_LPSPI3_SCK_SELECT_INPUT_GPIO_AD_B1_15_ALT2;
To see whether it is necessary it is easiest to search iMX.h for IOMUXC_x (where x is the name of the peripheral signal) -> IOMUXC_LPSPI3_SCK
If it shows up as a IOMUX_xxxx_SELECT_INPUT register, like:
#define IOMUXC_LPSPI3_SCK_SELECT_INPUT *(unsigned long *)(IOMUXC_SW_BLOCK + 0x0510) // LPSPI3_SCK_SELECT_INPUT DAISY register
#define IOMUXC_LPSPI3_SCK_SELECT_INPUT_GPIO_AD_B0_00_ALT7 0x00000000 // select GPIO_AD_B0_00 for mode: ALT7
#define IOMUXC_LPSPI3_SCK_SELECT_INPUT_GPIO_AD_B1_15_ALT2 0x00000001 // select GPIO_AD_B1_15 for mode: ALT2
it should be set.
IOMUXC_LPSPI3_SCK_SELECT_INPUT = IOMUXC_LPSPI3_SCK_SELECT_INPUT_GPIO_AD_B1_15_ALT2;
One can get away without setting it in case the 0x00000000 is true since it defaults to that, but as good practice it is best to always set the value. It also means that when modifying such configurations one doesn't forget to check and set the value accordingly.
If there is no corresponding IOMUXC_xxxxx_SELECT_INPUT register there is no sub-mux setting to be made.
6. After making such changes one can run the simulator and hover the mouse over the pins one wants to check and it will show the present GPIO/peripheral function so one can easily verify that it is correct before testing on HW.
Regards
Mark
