Linux Serial Driver
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The document provides detailed information about the Linux serial driver, focusing on settings such as frame formats, baud rates, flow control methods, and driver architecture. It includes examples of initializing and managing serial ports, as well as descriptions of key functions and structures related to serial communication. The document also touches on the termios structure for terminal I/O settings and presents API examples for configuring and using serial devices.
![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](https://image.slidesharecdn.com/linuxserialdriver-140907011529-phpapp01/85/Linux-Serial-Driver-11-320.jpg)
![#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](https://image.slidesharecdn.com/linuxserialdriver-140907011529-phpapp01/85/Linux-Serial-Driver-20-320.jpg)
![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);
}](https://image.slidesharecdn.com/linuxserialdriver-140907011529-phpapp01/85/Linux-Serial-Driver-22-320.jpg)
Linux Serial Driver
- 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
- 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); }