3.7 Function Calls Using Module Pointers

When writing drivers for module types that have multiple instances, the fact that all instances have the same register memory map can be utilized to make the driver reusable for all instances of the module type. If the driver takes a pointer argument pointing to the relevant module instance, the driver can be used for all modules of this type. This represents a great advantage when considering portability. Moreover, the written code may be portable between devices of the same family. Details on the compatibility between devices from the same family are provided in the data sheet’s series Overview section, and some differences are shown in Figure 3-6.

In a device with multiple timers/counters, the functions to initialize and access these modules can be shared by all module instances, instead of replicating the same lines of code for every instance. Even though there is a small overhead in passing the module pointer to the functions, the total code size will be reduced because the code is reused for all instances of each module type. Moreover, development time, maintenance cost, and portability can be greatly improved by using this approach.

The code below shows a function that uses a module pointer to select a clock source for any timer/counter module.

void TC_ConfigClockSource (volatile TCB_t *tc, TCB_CLKSEL_t clockSelection)
{
	tc->CTRLA = (tc->CTRLA & ~TCB_CLKSEL_gm) | clockSelection;
}

The function takes two arguments: A module pointer of type TCB_t and a group configuration type TCB_CLKSEL_t. The code in the function uses the timer/counter module pointer to access the CTRLA register and set a new clock selection for the timer/counter module with the address provided through the tc parameter. The code below shows how the function described above is used to set different configurations for different timer/counter instances.

/* Configure the TCB0 clock selection as CLKDIV2*/
TCB_ConfigClockSource (&TCB0, TCB_CLKSEL_CLKDIV2_gc); 
/* Configure the TCB0 clock selection as CLKDIV1*/
TCB_ConfigClockSource (&TCB0, TCB_CLKSEL_CLKDIV1_gc); 
/* Configure the TCB1 clock selection as CLKDIV2*/
TCB_ConfigClockSource (&TCB1, TCB_CLKSEL_CLKDIV2_gc); 
/* Configure the TCB2 clock selection as CLKDIV2*/
TCB_ConfigClockSource (&TCB2, TCB_CLKSEL_CLKDIV2_gc);