diff options
Diffstat (limited to 'src/lib')
| -rw-r--r-- | src/lib/uart8250.c | 31 |
1 files changed, 22 insertions, 9 deletions
diff --git a/src/lib/uart8250.c b/src/lib/uart8250.c index b2246713ca..fe8ed705d6 100644 --- a/src/lib/uart8250.c +++ b/src/lib/uart8250.c @@ -29,21 +29,30 @@ /* Should support 8250, 16450, 16550, 16550A type UARTs */ +/* Expected character delay at 1200bps is 9ms for a working UART + * and no flow-control. Assume UART as stuck if shift register + * or FIFO takes more than 50ms per character to appear empty. + * + * Estimated that inb() from UART takes 1 microsecond. + */ +#define SINGLE_CHAR_TIMEOUT (50 * 1000) +#define FIFO_TIMEOUT (16 * SINGLE_CHAR_TIMEOUT) + static inline int uart8250_can_tx_byte(unsigned base_port) { - return inb(base_port + UART_LSR) & UART_MSR_DSR; + return inb(base_port + UART_LSR) & UART_LSR_THRE; } static inline void uart8250_wait_to_tx_byte(unsigned base_port) { - while(!uart8250_can_tx_byte(base_port)) - ; + unsigned long int i = SINGLE_CHAR_TIMEOUT; + while (i-- && !uart8250_can_tx_byte(base_port)); } static inline void uart8250_wait_until_sent(unsigned base_port) { - while(!(inb(base_port + UART_LSR) & UART_LSR_TEMT)) - ; + unsigned long int i = FIFO_TIMEOUT; + while (i-- && !(inb(base_port + UART_LSR) & UART_LSR_TEMT)); } void uart8250_tx_byte(unsigned base_port, unsigned char data) @@ -64,9 +73,13 @@ int uart8250_can_rx_byte(unsigned base_port) unsigned char uart8250_rx_byte(unsigned base_port) { - while(!uart8250_can_rx_byte(base_port)) - ; - return inb(base_port + UART_RBR); + unsigned long int i = SINGLE_CHAR_TIMEOUT; + while (i-- && !uart8250_can_rx_byte(base_port)); + + if (i) + return inb(base_port + UART_RBR); + else + return 0x0; } void uart8250_init(unsigned base_port, unsigned divisor) @@ -83,7 +96,7 @@ void uart8250_init(unsigned base_port, unsigned divisor) /* DLAB on */ outb(UART_LCR_DLAB | CONFIG_TTYS0_LCS, base_port + UART_LCR); - /* Set Baud Rate Divisor. 12 ==> 115200 Baud */ + /* Set Baud Rate Divisor. 12 ==> 9600 Baud */ outb(divisor & 0xFF, base_port + UART_DLL); outb((divisor >> 8) & 0xFF, base_port + UART_DLM); |