Универсальный асинхронный приемо-передатчик: список регистров

  Unused

  RFF

Receive FIFO Full
This is used to indicate that the receive FIFO is completely full.
0: Receive FIFO not full
1: Receive FIFO Full
This bit is cleared when the RX FIFO is no longer full.

  RFNE

Receive FIFO Not Empty
This is used to indicate that the receive FIFO contains one or more entries.
0: Receive FIFO is empty
1: Receive FIFO is not empty
This bit is cleared when the RX FIFO is empty.

  TFE

Transmit FIFO Empty
This is used to indicate that the transmit FIFO is completely empty.
0: Transmit FIFO is not empty
1: Transmit FIFO is empty
This bit is cleared when the TX FIFO is no longer empty.

  TFNF

Transmit FIFO Not Full
This is used to indicate that the transmit FIFO in not full.
0: Transmit FIFO is full
1: Transmit FIFO is not full
This bit is cleared when the TX FIFO is full.

  BUSY

UART Busy Bit
0: Idle or inactive
1: Busy

Команда U-Boot для чтения регистра

Bit fields structure

typedef union  uart_usr
{
  struct
  {
   unsigned busy : 1;
   unsigned tfnf : 1;
   unsigned tfe : 1;
   unsigned rfne : 1;
   unsigned rff : 1;
   unsigned unused0 : 27;
  } b;
   unsigned long w;
} UART_USR