uart registers
| I/O port | Read (DLAB=0) | Write (DLAB=0) | Read (DLAB=1) | Write (DLAB=1) |
|---|---|---|---|---|
| base | RBR receiver buffer | THR transmitter holding | DLL divisor latch LSB | DLL divisor latch LSB |
| base+1 | IER interrupt enable | IER interrupt enable | DLM divisor latch MSB | DLM divisor latch MSB |
| base+2 | IIR interrupt identification | FCR FIFO control | IIR interrupt identification | FCR FIFO control |
| base+3 | LCR line control | LCR line control | LCR line control | LCR line control |
| base+4 | MCR modem control | MCR modem control | MCR modem control | MCR modem control |
| base+5 | LSR line status | factory test | LSR line status | factory test |
| base+6 | MSR modem status | not used | MSR modem status | not used |
| base+7 | SCR scratch | SCR scratch | SCR scratch | SCR scratch |
*from: https://www.lammertbies.nl/comm/info/serial-uart
uart hw driver
struct uart_port setup in probe func
设置serial_in/serial_out/handle_irq/set_termios函数指针，以及其它成员，比较关键的如下：
.iotype = UPIO_MEM,//成员表示该串口接口寄存器的地址类型，8位的内存地址
.regshift = 2,//在访问该串口接口的某个寄存器时，需把该寄存器的号左移多少位然后加基地址（不管是物理或虚拟地址）才能得能到这个寄存器的址址
.mapbase
.mapsize
.membase //ioremaped
static void 8250_mem_serial_out(struct uart_port *p, int offset, int value)
{
offset = offset << p->regshift;
writeb(value, p->membase + offset);
}
tty uart misc
查看ttyS0是否有开启
cat /sys/devices/platform/uart_control/uart_switch_status
执行结果如下：
001110220330
上面第3个字元如果为0，表示ttyS0是关闭的
Android系统开机过程中按ctrl c导致后面读stdin返回errno 5（IO error）
问题原因：sh启动比较晚
问题解决方案：sh启动要早，如果没有及时将read buf内的内容读走，可能会打乱tty driver，比如如下的启动时机（Android原生）
on init && property:ro.debuggable=1
start console