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Accessing Registers

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I/O Space Memory-Mapped Space

I/O Space

For registers in I/O space, use the xPC Target I/O read and write functions:

• Read functions

uint32_T xpcInpDW(uint16_T port );  // read a 32 bit word
uint16_T xpcInpW(uint16_T port );  // read a 16 bit word
uint8_T  xpcInpB(uint16_T port );  // read an 8 bit byte

• Write functions

void xpcOutpDW(uint16_T port, uint32_T value );  // write 32 bits
void xpcOutpW(uint16_T port, uint16_T value );  // write 16 bits
void xpcOutpB(uint8_T port,  uint8_T value );  // write a byte

The port address is the value returned in the BaseAddress array.

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Memory-Mapped Space

For registers in memory-mapped space, access them by dereferencing through a pointer that contains the virtual address returned by the xpcReserveMemoryRegion function. Because modern compilers have aggressive optimizers, you must declare the pointer to be volatile. Doing so ensures that the compiler does not optimize out reads and writes using that pointer. The following pseudocode illustrates this using two methods: structure and array.

• Structure

  struct bdregs {
      volatile int reg1;
      volatile int reg2;
      etc.
  };
  
      struct bdregs *regs = pciInfo.VirtualAddress[1];
  
      regs->reg1 = 0x1234;  // Sets reg1 to that value
      regs->reg2 = 0x56789abc;
      etc.

  If your hardware uses registers with different lengths, it might be easier to use the structure method.

• Array

  #define REG1   0
  #define REG2   1
  etc.
  
      volatile int *aregs = pciInfo.VirtualAddress[1];
  
      aregs[REG1] = 0x1234;
      aregs[REG2] = 0x56789abc;

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Passing Parameters

Creating Custom Drivers Using the xPC Target Driver Authoring Tool

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