6.4.7. UART State

struct regs is used to hold the value of each register. There are ten of these, since register 0 is really two registers, depending on whether it is being read (rbr) or written (thr) and the divisor latch is really an extra 16 bit register.

  struct {
    unsigned char       rbr;            // R: Rx buffer,
    unsigned char       thr;            // R: Tx hold reg,
    unsigned char       ier;            // R/W: Interrupt Enable Register
    unsigned char       iir;            // R: Interrupt ID Register
    unsigned char       lcr;            // R/W: Line Control Register
    unsigned char       mcr;            // W: Modem Control Register
    unsigned char       lsr;            // R: Line Status Register
    unsigned char       msr;            // R: Modem Status Register
    unsigned char       scr;            // R/W: Scratch Register            
    unsigned short int  dl;             // R/W: Divisor Latch
  } regs;

An additional register, intrPending, holds flags (corresponding to the interrupt enable register bits) indicating which interrupts are currently pending. A flag initialized at construction records the model endianness, isLittleEndian.