PAD Multiplexing

Many of the IO pads on the chip can be connected to a variety of different devices and have a variety of properties that need to be configured. A pad descriptor is created by the CYGHWR_HAL_IMX_PAD() macro. The pad argument defines the pad to be configured, and follows the hardware naming convention, for example AD_B0(12) or SD_B1(3). The mode argument is the terminal part of a CYGHWR_HAL_IMX_PAD_MODE_XXXX macro; this may be one supplied in the HAL, or one constructed by the driver or application. This macro is defined as a combination of the CYGHWR_HAL_IMX_PAD_MODE_ definitions in cyg/hal/var_io.h, which correspond to the definitions in the hardware pad MUX and CTL registers.

The macro CYGHWR_HAL_IMX_PAD_SET() is used to configure a pad according to the descriptor.

The following example shows how the LPUART pads are configured.

#define CYGHWR_HAL_IMX_PAD_MODE_LPUART_PAD(__alt)       \
        CYGHWR_HAL_IMX_PAD_MODE_MUX(__alt)      |       \
        CYGHWR_HAL_IMX_PAD_MODE_PUE             |       \
        CYGHWR_HAL_IMX_PAD_MODE_PKE             |       \
        CYGHWR_HAL_IMX_PAD_MODE_PUS_47K_PU      |       \
        CYGHWR_HAL_IMX_PAD_MODE_DSE(6)          |       \
        CYGHWR_HAL_IMX_PAD_MODE_SPEED_MED2

#define CYGHWR_HAL_IMX_LPUART1_TX       CYGHWR_HAL_IMX_PAD( AD_B0(12), LPUART_PAD(2) )
#define CYGHWR_HAL_IMX_LPUART1_RX       CYGHWR_HAL_IMX_PAD( AD_B0(13), LPUART_PAD(2) )
        

PAD Daisy Chaining

Some device IO lines can connect to multiple pads, the daisy chain registers select which pad is to be used for the device. A daisy chain descriptor is created by the CYGHWR_HAL_IMX_DAISY macro. The reg argument selects which daisy chain device line is to be programmed, and the val argument defines the pad selection. Both of these arguments are fragments of macros defined in cyg/hal/var_io.h. Only registers and values currently used are defined there, new ones can be added there or defined in the driver or application.

The CYGHWR_HAL_IMX_DAISY_SET macro is called to program the configuration from a descriptor into the hardware.

The following example shows some daisy chain descriptor definitions.

#  define CYGHWR_HAL_NXP_LPUART3_TXD_DAISY CYGHWR_HAL_IMX_DAISY(LPUART3_TX, AD_B1_06_ALT2)

#  define CYGHWR_HAL_NXP_LPUART3_RXD_DAISY CYGHWR_HAL_IMX_DAISY(LPUART3_RX, AD_B1_07_ALT2)

#  define CYGHWR_HAL_NXP_LPUART3_CTS_DAISY CYGHWR_HAL_IMX_DAISY(LPUART3_CTS_B, AD_B1_04_ALT2)
#  define CYGHWR_HAL_NXP_LPUART3_RTS_DAISY CYGHWR_HAL_IMX_DAISY_NONE
        

Clock Gating Control

Most device clocks are controlled by a gate that needs to be switched on or off. The HAL provides macros which may be used to enable or disable peripheral clocks. Effectively this indicates whether the peripheral is powered on (enabled) or powered down (disabled), and so may be used to ensure unused peripherals are turned off to save power. The macro CYGHWR_HAL_IMX_CLOCK_GATE() defines a clock gate descriptor. The reg argument gives the CCGR register to be used and the gate argument selects the clock gate bit in that register. Clock gate descriptors are defined in cyg/hal/var_io.h and new values will be added there as needed.

The macros CYGHWR_HAL_IMX_CLOCK_ENABLE() and CYGHWR_HAL_IMX_CLOCK_DISABLE() enable and disable the clock described by the descriptor. At present clocks are either fully on or fully off, the option to switch clocks off in WAIT mode is not implemented.

It is important to remember that before a peripheral can be used, it must be enabled. It is safe to re-enable a peripheral that is already enabled, although usually a device driver will only do so once in its initialization. eCos will automatically initialize some peripheral blocks where it needs to use the associated peripherals, and in eCos-supplied device drivers which are included in the eCos configuration. However this should not be relied on - it is always safest to enable the peripheral clocks anyway just in case.

GPIO

A descriptor is created by the CYGHWR_HAL_IMX_GPIO() macro. The ctlr argument selects the GPIO controller while the pin argument selects the GPIO pin in the controller. The mode argument configures the pin within the GPIO controller. At present interrupt configuration is not supported, so the mode may only be IN or OUT. In addition to GPIO configuration, the matching pad will need to be configured using a PAD descriptor.

If a GPIO pin has been configured as an output then its value may be set using CYGHWR_HAL_IMX_GPIO_OUT(). Similarly the current value of an input pin can be read using CYGHWR_HAL_IMX_GPIO_IN().