May 01, 2005
Register Access in C++
Listing 10
// A macro that defines enumeration values for a bitset
// You supply the start and end bit positions
#define REG_BIT_DEFN(start, end) ((start<<16)|(end-start+1))
enum STATUS_bits
{
TX_BUFFER_EMPTY = REG_BIT_DEFN(0, 0),
RX_BUFFER_EMPTY = REG_BIT_DEFN(1, 1),
TX_UNDERRUN = REG_BIT_DEFN(2, 2),
RX_OVERFLOW = REG_BIT_DEFN(3, 3)
};
... similarly for other bitsets ...
#undef REG_BIT_DEFN
inline uint32_t bitRead(Registers32 reg, uint32_t bits)
{
uint32_t regval = *regAddress(reg);
const uint32_t width = bits & 0xff;
const uint32_t bitno = bits >> 16;
regval >>= bitno;
regval &= ((1<<width)-1);
return regval;
}
inline void bitWrite(Registers32 reg, uint32_t bits, uint32_t value)
{
uint32_t regval = *regAddress(reg);
const uint32_t width = bits & 0xff;
const uint32_t bitno = bits >> 16;
regval &= ~(((1<<width)-1) << bitno);
regval |= value << bitno;
*regAddress(reg) = regval;
}
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