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1. LINUX SERIAL DRIVER
1

2. 2
Byte Frame
8N1 signifies 8 Data bits, No Parity and 1 Stop Bit
TTL/CMOS Serial Logic Waveform
RS-232 Logic Waveform
Frame

3. Baud rate
1) 50 – 921.6kbps
Data bits
1) 5, 6, 7, 8
Parity
1) None, Odd, Even, Mark, Space
Stop bits
1) 1, 1.5/2 (1.5 for data bits=5)
Flow control
1) RTS/CTS, Xon/Xoff, DTR/DSR
3
Serial Parameter/Setting
N81 is common used in RS-232.
Sometimes E71/E72/O71/O72 will also be selected.

4. Modem line (in/out define)
Neck Name In/Out Comment
RTS Out Control the remote send or pause, to do
flow control
CTS In the remote note me to send or not, to do
flow control
DTR Out DTE ready, the old method to do flow
control
DSR In DCE ready, the old method to do flow
control
DCD In for DTE
Out for DCE
to indicate the phone is hank off
RI In for DTE
Out for DCE
Ring, the telephone is ringed

5. 5
How to connect to remote – RS232
Tx
Rx
RTS
CTS
DTR
DSR
DCD
RI
Tx
Rx
RTS
CTS
DTR
DSR
DCD
RI

6. Hardware flow control to use RTS/CTS
1) RTS low to let the remoter to stop transmitting
2) RTS high to let the remoter to restart transmitting
3) CTS low to stop my transmitting
4) CTS high to restart my transmitting
Software flow control to use some character, so the data must
be escape it
1) Send Xoff to let the remoter to stop transmitting
2) Send Xon to let the remoter to restart transmitting
3) Receive Xoff to stop my transmitting
4) Receive Xon to restart my transmitting
6
Flow control

7. 7
Flow Control with RTS/CTS (H/W)
Tx
Tx
Rx
Rx
Rx Buffer
low
high
RTS
CTS
high
low

8. 8
Flow Control with Xon/Xoff (S/W)
Tx
Tx
Rx
Rx
Rx Buffer
low
high
Xoff
Xon
Xoff
Xon

9. 9
Serial Device Driver Architecture
Hardware Serial Device
Serial Device Driver
tty Device Driver
Line description Device Driver
Application by termio/termios API Kernel
To do the basic
terminal
read/write/ioc
tl control
To control the
hardware
receive/transfer
To do about
the terminal
control

10. 8250是一種不成文的硬件規格
原始碼所在目錄：drivers/serial
SoC的serial port通常都會使用
10
標準8250 serial device driver
serial_core.c
8250.c
tty
console

11. 宣告一個resource sturcture如下:
static struct uart_port my_uart_init[] __initdata = {
[0] = {
.membase = VA_UART_BASE, // virtual address
.mapbase = PA_UART_BASE, // physical address
.irq = IRQ_UART,
.flags = UPF_SKIP_TEST,
.iotype = UPIO_MEM32,
.regshift = 2,
.uartclk = 921600 * 16,
.line = 0, // which port number on system
.type = PORT_16550A,
.fifosize = 16,
},
};
呼叫kernel API加入
early_serial_setup(&my_uart_init[0]); // embedded UART port
11
如何增加一個8250的port

12. Examlpe
MACHINE_START(MOXACPU, "Moxa CPU development platform")
.phys_io = 0x80000000,
.io_pg_offst = ((IO_ADDRESS(0x80000000)>>18)&0xfffc),
.map_io = map_io,
.init_irq = irq_init_irq,
.timer = &moxacpu_timer,
.fixup = fixup,
.boot_params = 0x100,
.init_machine = moxacpu_init,
MACHINE_END
void __init map_io(void)
{
iotable_init(mycpu_io_desc, sizeof(mycpu_io_desc)/sizeof(struct
map_desc));
early_serial_setupS

13. 除了標準的8250暫存器之外，還有其它額
外的暫存器
FIFO大小通常是大於16個
會有多個port在系統上
有的會有CPU的智能卡
13
非標準的8250 serial driver

14. struct tty_driver myuart_sdriver =
alloc_tty_driver(TOTAL_PORTS);
Initialize the tty_driver structure
myuart_sdriver->owner = THIS_MODULE;
myuart_sdriver->magic = TTY_DRIVER_MAGIC;
myuart_sdriver->name = "ttyMI";
myuart_sdriver->major = ttymajor;
myuart_sdriver->minor_start = 0;
myuart_sdriver->num = MXSER_PORTS + 1;
myuart_sdriver->type = TTY_DRIVER_TYPE_SERIAL;
myuart_sdriver->subtype = SERIAL_TYPE_NORMAL;
myuart_sdriver->init_termios = tty_std_termios;
myuart_sdriver->init_termios.c_cflag = B9600|CS8|CREAD|HUPCL|CLOCAL;
myuart_sdriver->flags = TTY_DRIVER_REAL_RAW|TTY_DRIVER_DYNAMIC_DEV;
tty_set_operations(myuart_sdriver, &myuart_ops);
retval = tty_register_driver(myuart_sdriver);
tty_register_device(myuart_sdriver, ports, NULL);
14
Driver的初始化

15. static const struct tty_operations mxser_ops = {
.open = myuart_open,
.close = myuart_close,
.write = myuart_write,
.put_char = myuart_put_char,
.flush_chars = myuart_flush_chars,
.write_room = myuart_write_room,
.chars_in_buffer = myuart_chars_in_buffer,
.flush_buffer = myuart_flush_buffer,
.ioctl = myuart_ioctl,
.throttle = myuart_throttle,
.unthrottle = myuart_unthrottle,
.set_termios = myuart_set_termios,
.stop = myuart_stop,
.start = myuart_start,
.hangup = myuart_hangup,
.break_ctl = myuart_rs_break,
.wait_until_sent = myuart_wait_until_sent,
.tiocmget = myuart_tiocmget,
.tiocmset = myuart_tiocmset,
};
15
Set tty operations

16. Driver Initialize Example
static int __init mxser_module_init(void)
{
mxvar_sdriver = alloc_tty_driver(MXSER_PORTS + 1);
mxvar_sdriver->name = "ttyMI";
mxvar_sdriver->major = ttymajor;
mxvar_sdriver->minor_start = 0;
mxvar_sdriver->num = MXSER_PORTS + 1;
mxvar_sdriver->type = TTY_DRIVER_TYPE_SERIAL;
mxvar_sdriver->subtype = SERIAL_TYPE_NORMAL;
mxvar_sdriver->init_termios = tty_std_termios;
mxvar_sdriver->init_termios.c_cflag =B9600|CS8|CREAD|HUPCL|CLOCAL;
mxvar_sdriver->flags = TTY_DRIVER_REAL_RAW|TTY_DRIVER_DYNAMIC_DEV;
tty_set_operations(mxvar_sdriver, &mxser_ops);
retval = tty_register_driver(mxvar_sdriver);
retval = request_irq(brd->irq, mxser_interrupt, IRQF_SHARED, "mxser",
brd);
…………………………..
for (i = 0; i < brd->info->nports; i++)
tty_register_device(mxvar_sdriver, brd->idx + i, NULL);
……………………….
return 0;
}

17. Driver Open/Close Example
static int mxser_open(struct tty_struct *tty, struct file *filp)
{
port = tty->index; // minor or port number
tty->driver_data = info; // set private data
spin_lock_irqsave(&info->slock, flags);
info->port.count++;
spin_unlock_irqrestore(&info->slock, flags);
retval = mxser_startup(info);
return 0;
}
static void mxser_close(struct tty_struct *tty, struct file *filp)
{
struct mxser_port *info = tty->driver_data;
if (--info->port.count) {
return;
}
…………………………
if (info->port.closing_wait != ASYNC_CLOSING_WAIT_NONE)
tty_wait_until_sent(tty, info->port.closing_wait);
mxser_shutdown(info);
mxser_flush_buffer(tty);
tty_ldisc_flush(tty);
}

18. Driver Write Example
static int mxser_write(struct tty_struct *tty, const unsigned char *buf, int count)
{
………………………..
while (1) {
…………………..
memcpy(info->port.xmit_buf + info->xmit_head, buf, c);
…………………..
}
if (info->xmit_cnt && !tty->stopped) {
if (!tty->hw_stopped ||
(info->type == PORT_16550A) ||
(info->board->chip_flag)) {
spin_lock_irqsave(&info->slock, flags);
outb(info->IER & ~UART_IER_THRI, info->ioaddr +
UART_IER);
info->IER |= UART_IER_THRI;
outb(info->IER, info->ioaddr + UART_IER);
spin_unlock_irqrestore(&info->slock, flags);
}
}
return total;
}

19. Receive Interrupt Example
recv_room = tty->receive_room;
if ((recv_room == 0) && (!port->ldisc_stop_rx))
mxser_stoprx(tty);
…………………………………
while (gdl--) {
ch = inb(port->ioaddr + UART_RX);
tty_insert_flip_char(tty, ch, 0);
cnt++;
}
…………………………………..
spin_unlock(&port->slock);
tty_flip_buffer_push(tty);
spin_lock(&port->slock);
……………………………

20. #define NCCS 32
struct termios
{
tcflag_t c_iflag; /* input mode flags */
tcflag_t c_oflag; /* output mode flags */
tcflag_t c_cflag; /* control mode flags */
tcflag_t c_lflag; /* local mode flags */
cc_t c_line; /* line discipline */
cc_t c_cc[NCCS]; /* control characters */
speed_t c_ispeed; /* input speed */
speed_t c_ospeed; /* output speed */
#define _HAVE_STRUCT_TERMIOS_C_ISPEED 1
#define _HAVE_STRUCT_TERMIOS_C_OSPEED 1
};
20
termios structure
/* c_cc characters */
#define VINTR 0
#define VQUIT 1
#define VERASE 2
#define VKILL 3
#define VEOF 4
#define VTIME 5
#define VMIN 6
#define VSWTC 7
#define VSTART 8
#define VSTOP 9
#define VSUSP 10
#define VEOL 11
#define VREPRINT 12
#define VDISCARD 13
#define VWERASE 14
#define VLNEXT 15
#define VEOL2 16

21. #include <termios.h>
#include <unistd.h>
int tcgetattr(int fd, struct termios *termios_p);
int tcsetattr(int fd, int optional_actions, const struct termios *termios_p);
int tcsendbreak(int fd, int duration);
int tcdrain(int fd);
int tcflush(int fd, int queue_selector);
int tcflow(int fd, int action);
void cfmakeraw(struct termios *termios_p);
speed_t cfgetispeed(const struct termios *termios_p);
speed_t cfgetospeed(const struct termios *termios_p);
int cfsetispeed(struct termios *termios_p, speed_t speed);
int cfsetospeed(struct termios *termios_p, speed_t speed);
int cfsetspeed(struct termios *termios_p, speed_t speed);
21
API

22. AP example
#include <termios.h>
int main(int argc, char *argv[])
{
int fd;
struct termios trem;
fd = open(“/dev/ttyS0”, O_RDWR);
tcgetattr(fd, &term);
term.lflag = 0;
term.iflag = 0;
term.cflag = B115200 | CS8|CREAD|CLOCAL;
term.oflag = 0;
term.c_cc[VMIN] = 1;
term.c_cc[VTIME] = 1;
tcsetattr(fd, TCDRAIN, &term);
tcflush(fd,TCIOFLUSH);
……………
write(fd, buf, len);
……………………
read(fd, buf, len);
………………..
close(fd);
}