Programmed I/O

Input and output operations are made by a program running on the processor.

Disadvantage: Inefficient - too much polling for general use. Interrupt driven I/O is more efficient.

#define IO_BASE 0xFFFC1000 // or whatever #define U_SEND 0x10 #define U_RECEIVE 0x14 #define U_CONTROL 0x18 #define U_STATUS 0x1C #define UART_SEND() \ (*((volatile char *)(IO_BASE+U_SEND))) #define UART_RECEIVE() \ (*((volatile char *)(IO_BASE+U_RECEIVE))) #define UART_CONTROL() \ (*((volatile char *)(IO_BASE+U_CONTROL))) #define UART_STATUS() \ (*((volatile char *)(IO_BASE+U_STATUS))) #define UART_STATUS_RX_EMPTY (0x80) #define UART_STATUS_TX_EMPTY (0x40) #define UART_CONTROL_RX_INT_ENABLE (0x20) #define UART_CONTROL_TX_INT_ENABLE (0x10)

char uart_polled_read() { while (UART_STATUS() & UART_STATUS_RX_EMPTY) continue; return UART_RECEIVE(); } uart_polled_write(char d) { while (!(UART_STATUS() & UART_STATUS_TX_EMPTY)) continue; UART_SEND() = d; }