#include /*---------------------------------------------------------------------------* * rs232.c - serial driver for 8250 and 16450 UARTs * * Added support for Atari ST M68901 and YM-2149 --kub * *---------------------------------------------------------------------------*/ #include #include #include #include "tty.h" #if NR_RS_LINES > 0 /* 8250 constants. */ #define UART_FREQ 115200L /* timer frequency */ /* Interrupt enable bits. */ #define IE_RECEIVER_READY 1 #define IE_TRANSMITTER_READY 2 #define IE_LINE_STATUS_CHANGE 4 #define IE_MODEM_STATUS_CHANGE 8 /* Interrupt status bits. */ #define IS_MODEM_STATUS_CHANGE 0 #define IS_TRANSMITTER_READY 2 #define IS_RECEIVER_READY 4 #define IS_LINE_STATUS_CHANGE 6 /* Line control bits. */ #define LC_2STOP_BITS 0x04 #define LC_PARITY 0x08 #define LC_PAREVEN 0x10 #define LC_BREAK 0x40 #define LC_ADDRESS_DIVISOR 0x80 /* Line status bits. */ #define LS_OVERRUN_ERR 2 #define LS_PARITY_ERR 4 #define LS_FRAMING_ERR 8 #define LS_BREAK_INTERRUPT 0x10 #define LS_TRANSMITTER_READY 0x20 /* Modem control bits. */ #define MC_DTR 1 #define MC_RTS 2 #define MC_OUT2 8 /* required for PC & AT interrupts */ /* Modem status bits. */ #define MS_CTS 0x10 #define MS_RLSD 0x80 /* Received Line Signal Detect */ #define MS_DRLSD 0x08 /* RLSD Delta */ #define DATA_BITS_SHIFT 8 /* amount data bits shifted in mode */ #define DEF_BAUD 1200 /* default baud rate */ #define RS_IBUFSIZE 1024 /* RS232 input buffer size */ #define RS_OBUFSIZE 1024 /* RS232 output buffer size */ /* Input buffer watermarks. * The external device is asked to stop sending when the buffer * exactly reaches high water, or when TTY requests it. Sending restarts * when the input buffer empties below the low watermark. */ #define RS_ILOWWATER (1 * RS_IBUFSIZE / 4) #define RS_IHIGHWATER (3 * RS_IBUFSIZE / 4) /* Output buffer low watermark. * TTY is notified when the output buffer empties below the low watermark, so * it may continue filling the buffer if doing a large write. */ #define RS_OLOWWATER (1 * RS_OBUFSIZE / 4) /* Macros to handle flow control. * Interrupts must be off when they are used. * Time is critical - already the function call for outb() is annoying. * If outb() can be done in-line, tests to avoid it can be dropped. * istart() tells external device we are ready by raising RTS. * istop() tells external device we are not ready by dropping RTS. * DTR is kept high all the time (it probably should be raised by open and * dropped by close of the device). * OUT2 is also kept high all the time. */ #define istart(rs) \ (sys_outb((rs)->modem_ctl_port, MC_OUT2 | MC_RTS | MC_DTR), \ (rs)->idevready = TRUE) #define istop(rs) \ (sys_outb((rs)->modem_ctl_port, MC_OUT2 | MC_DTR), \ (rs)->idevready = FALSE) /* Macro to tell if device is ready. The rs->cts field is set to MS_CTS if * CLOCAL is in effect for a line without a CTS wire. */ #define devready(rs) ((my_inb(rs->modem_status_port) | rs->cts) & MS_CTS) /* Macro to tell if transmitter is ready. */ #define txready(rs) (my_inb(rs->line_status_port) & LS_TRANSMITTER_READY) /* Macro to tell if carrier has dropped. * The RS232 Carrier Detect (CD) line is usually connected to the 8250 * Received Line Signal Detect pin, reflected by bit MS_RLSD in the Modem * Status Register. The MS_DRLSD bit tells if MS_RLSD has just changed state. * So if MS_DRLSD is set and MS_RLSD cleared, we know that carrier has just * dropped. */ #define devhup(rs) \ ((my_inb(rs->modem_status_port) & (MS_RLSD|MS_DRLSD)) == MS_DRLSD) /* Types. */ typedef unsigned char bool_t; /* boolean */ /* RS232 device structure, one per device. */ typedef struct rs232 { tty_t *tty; /* associated TTY structure */ int icount; /* number of bytes in the input buffer */ char *ihead; /* next free spot in input buffer */ char *itail; /* first byte to give to TTY */ bool_t idevready; /* nonzero if we are ready to receive (RTS) */ char cts; /* normally 0, but MS_CTS if CLOCAL is set */ unsigned char ostate; /* combination of flags: */ #define ODONE 1 /* output completed (< output enable bits) */ #define ORAW 2 /* raw mode for xoff disable (< enab. bits) */ #define OWAKEUP 4 /* tty_wakeup() pending (asm code only) */ #define ODEVREADY MS_CTS /* external device hardware ready (CTS) */ #define OQUEUED 0x20 /* output buffer not empty */ #define OSWREADY 0x40 /* external device software ready (no xoff) */ #define ODEVHUP MS_RLSD /* external device has dropped carrier */ #define OSOFTBITS (ODONE | ORAW | OWAKEUP | OQUEUED | OSWREADY) /* user-defined bits */ #if (OSOFTBITS | ODEVREADY | ODEVHUP) == OSOFTBITS /* a weak sanity check */ #error /* bits are not unique */ #endif unsigned char oxoff; /* char to stop output */ bool_t inhibited; /* output inhibited? (follows tty_inhibited) */ bool_t drain; /* if set drain output and reconfigure line */ int ocount; /* number of bytes in the output buffer */ char *ohead; /* next free spot in output buffer */ char *otail; /* next char to output */ #if (MACHINE == IBM_PC) port_t xmit_port; /* i/o ports */ port_t recv_port; port_t div_low_port; port_t div_hi_port; port_t int_enab_port; port_t int_id_port; port_t line_ctl_port; port_t modem_ctl_port; port_t line_status_port; port_t modem_status_port; #endif unsigned char lstatus; /* last line status */ unsigned char pad; /* ensure alignment for 16-bit ints */ unsigned framing_errors; /* error counts (no reporting yet) */ unsigned overrun_errors; unsigned parity_errors; unsigned break_interrupts; int irq; /* irq for this line */ int irq_hook_id; /* interrupt hook */ char ibuf[RS_IBUFSIZE]; /* input buffer */ char obuf[RS_OBUFSIZE]; /* output buffer */ } rs232_t; static rs232_t rs_lines[NR_RS_LINES]; #if (MACHINE == IBM_PC) /* 8250 base addresses. */ static port_t addr_8250[] = { 0x3F8, /* COM1 */ 0x2F8, /* COM2 */ 0x3E8, /* COM3 */ 0x2E8, /* COM4 */ }; #endif static void in_int(rs232_t *rs); static void line_int(rs232_t *rs); static void modem_int(rs232_t *rs); static int rs_write(tty_t *tp, int try); static void rs_echo(tty_t *tp, int c); static int rs_ioctl(tty_t *tp, int try); static void rs_config(rs232_t *rs); static int rs_read(tty_t *tp, int try); static int rs_icancel(tty_t *tp, int try); static int rs_ocancel(tty_t *tp, int try); static void rs_ostart(rs232_t *rs); static int rs_break(tty_t *tp, int try); static int rs_close(tty_t *tp, int try); static void out_int(rs232_t *rs); static void rs232_handler(rs232_t *rs); /* XXX */ static void lock(void) {} static void unlock(void) {} static int my_inb(port_t port) { int r; u32_t v = 0; r = sys_inb(port, &v); if (r != OK) printf("RS232 warning: failed inb 0x%x\n", port); return (int) v; } /*===========================================================================* * rs_write * *===========================================================================*/ static int rs_write(register tty_t *tp, int try) { /* (*devwrite)() routine for RS232. */ rs232_t *rs = tp->tty_priv; int count, ocount; if (rs->inhibited != tp->tty_inhibited) { /* Inhibition state has changed. */ lock(); rs->ostate |= OSWREADY; if (tp->tty_inhibited) rs->ostate &= ~OSWREADY; unlock(); rs->inhibited = tp->tty_inhibited; } if (rs->drain) { /* Wait for the line to drain then reconfigure and continue output. */ if (rs->ocount > 0) return 0; rs->drain = FALSE; rs_config(rs); } /* While there is something to do. */ for (;;) { ocount = buflen(rs->obuf) - rs->ocount; count = bufend(rs->obuf) - rs->ohead; if (count > ocount) count = ocount; if (count > tp->tty_outleft) count = tp->tty_outleft; if (count == 0 || tp->tty_inhibited) { if (try) return 0; break; } if (try) return 1; /* Copy from user space to the RS232 output buffer. */ sys_safecopyfrom(tp->tty_outcaller, tp->tty_outgrant, tp->tty_outoffset, (vir_bytes) rs->ohead, count, D); /* Perform output processing on the output buffer. */ out_process(tp, rs->obuf, rs->ohead, bufend(rs->obuf), &count, &ocount); if (count == 0) break; /* Assume echoing messed up by output. */ tp->tty_reprint = TRUE; /* Bookkeeping. */ lock(); /* protect interrupt sensitive rs->ocount */ rs->ocount += ocount; rs_ostart(rs); unlock(); if ((rs->ohead += ocount) >= bufend(rs->obuf)) rs->ohead -= buflen(rs->obuf); tp->tty_outoffset += count; tp->tty_outcum += count; if ((tp->tty_outleft -= count) == 0) { /* Output is finished, reply to the writer. */ if(tp->tty_outrepcode == TTY_REVIVE) { notify(tp->tty_outcaller); tp->tty_outrevived = 1; } else { tty_reply(tp->tty_outrepcode, tp->tty_outcaller, tp->tty_outproc, tp->tty_outcum); tp->tty_outcum = 0; } } } if (tp->tty_outleft > 0 && tp->tty_termios.c_ospeed == B0) { /* Oops, the line has hung up. */ if(tp->tty_outrepcode == TTY_REVIVE) { notify(tp->tty_outcaller); tp->tty_outrevived = 1; } else { tty_reply(tp->tty_outrepcode, tp->tty_outcaller, tp->tty_outproc, EIO); tp->tty_outleft = tp->tty_outcum = 0; } } return 1; } /*===========================================================================* * rs_echo * *===========================================================================*/ static void rs_echo(tp, c) tty_t *tp; /* which TTY */ int c; /* character to echo */ { /* Echo one character. (Like rs_write, but only one character, optionally.) */ rs232_t *rs = tp->tty_priv; int count, ocount; ocount = buflen(rs->obuf) - rs->ocount; if (ocount == 0) return; /* output buffer full */ count = 1; *rs->ohead = c; /* add one character */ out_process(tp, rs->obuf, rs->ohead, bufend(rs->obuf), &count, &ocount); if (count == 0) return; lock(); rs->ocount += ocount; rs_ostart(rs); unlock(); if ((rs->ohead += ocount) >= bufend(rs->obuf)) rs->ohead -= buflen(rs->obuf); } /*===========================================================================* * rs_ioctl * *===========================================================================*/ static int rs_ioctl(tty_t *tp, int UNUSED(dummy)) /* tp; which TTY */ { /* Reconfigure the line as soon as the output has drained. */ rs232_t *rs = tp->tty_priv; rs->drain = TRUE; return 0; /* dummy */ } /*===========================================================================* * rs_config * *===========================================================================*/ static void rs_config(rs232_t *rs) /* rs which line */ { /* Set various line control parameters for RS232 I/O. * If DataBits == 5 and StopBits == 2, 8250 will generate 1.5 stop bits. * The 8250 can't handle split speed, so we use the input speed. */ tty_t *tp = rs->tty; int divisor; int line_controls; static struct speed2divisor { speed_t speed; int divisor; } s2d[] = { #if (MACHINE == IBM_PC) { B50, UART_FREQ / 50 }, #endif { B75, UART_FREQ / 75 }, { B110, UART_FREQ / 110 }, { B134, UART_FREQ * 10 / 1345 }, { B150, UART_FREQ / 150 }, { B200, UART_FREQ / 200 }, { B300, UART_FREQ / 300 }, { B600, UART_FREQ / 600 }, { B1200, UART_FREQ / 1200 }, #if (MACHINE == IBM_PC) { B1800, UART_FREQ / 1800 }, #endif { B2400, UART_FREQ / 2400 }, { B4800, UART_FREQ / 4800 }, { B9600, UART_FREQ / 9600 }, { B19200, UART_FREQ / 19200 }, #if (MACHINE == IBM_PC) { B38400, UART_FREQ / 38400 }, { B57600, UART_FREQ / 57600 }, { B115200, UART_FREQ / 115200L }, #endif }; struct speed2divisor *s2dp; /* RS232 needs to know the xoff character, and if CTS works. */ rs->oxoff = tp->tty_termios.c_cc[VSTOP]; rs->cts = (tp->tty_termios.c_cflag & CLOCAL) ? MS_CTS : 0; /* Look up the 8250 rate divisor from the output speed. */ divisor = 0; for (s2dp = s2d; s2dp < s2d + sizeof(s2d)/sizeof(s2d[0]); s2dp++) { if (s2dp->speed == tp->tty_termios.c_ospeed) divisor = s2dp->divisor; } if (divisor == 0) return; /* B0? */ /* Compute line control flag bits. */ line_controls = 0; if (tp->tty_termios.c_cflag & PARENB) { line_controls |= LC_PARITY; if (!(tp->tty_termios.c_cflag & PARODD)) line_controls |= LC_PAREVEN; } if (divisor >= (UART_FREQ / 110)) line_controls |= LC_2STOP_BITS; line_controls |= (tp->tty_termios.c_cflag & CSIZE) >> 2; /* Lock out interrupts while setting the speed. The receiver register is * going to be hidden by the div_low register, but the input interrupt * handler relies on reading it to clear the interrupt and avoid looping * forever. */ lock(); /* Select the baud rate divisor registers and change the rate. */ sys_outb(rs->line_ctl_port, LC_ADDRESS_DIVISOR); sys_outb(rs->div_low_port, divisor); sys_outb(rs->div_hi_port, divisor >> 8); /* Change the line controls and reselect the usual registers. */ sys_outb(rs->line_ctl_port, line_controls); rs->ostate = devready(rs) | ORAW | OSWREADY; /* reads modem_ctl_port */ if ((tp->tty_termios.c_lflag & IXON) && rs->oxoff != _POSIX_VDISABLE) rs->ostate &= ~ORAW; unlock(); } /*===========================================================================* * rs_init * *===========================================================================*/ void rs_init(tty_t *tp) /* tp which TTY */ { u32_t dummy; /* Initialize RS232 for one line. */ register rs232_t *rs; int line; port_t this_8250; int irq; char l[10]; /* Associate RS232 and TTY structures. */ line = tp - &tty_table[NR_CONS]; /* See if kernel debugging is enabled; if so, don't initialize this * serial line, making tty not look at the irq and returning ENXIO * for all requests on it from userland. (The kernel will use it.) */ if(env_get_param(SERVARNAME, l, sizeof(l)-1) == OK && atoi(l) == line) { return; } rs = tp->tty_priv = &rs_lines[line]; rs->tty = tp; /* Set up input queue. */ rs->ihead = rs->itail = rs->ibuf; /* Precalculate port numbers for speed. Magic numbers in the code (once). */ this_8250 = addr_8250[line]; rs->xmit_port = this_8250 + 0; rs->recv_port = this_8250 + 0; rs->div_low_port = this_8250 + 0; rs->div_hi_port = this_8250 + 1; rs->int_enab_port = this_8250 + 1; rs->int_id_port = this_8250 + 2; rs->line_ctl_port = this_8250 + 3; rs->modem_ctl_port = this_8250 + 4; rs->line_status_port = this_8250 + 5; rs->modem_status_port = this_8250 + 6; /* Set up the hardware to a base state, in particular * o turn off DTR (MC_DTR) to try to stop the external device. * o be careful about the divisor latch. Some BIOS's leave it enabled * here and that caused trouble (no interrupts) in version 1.5 by * hiding the interrupt enable port in the next step, and worse trouble * (continual interrupts) in an old version by hiding the receiver * port in the first interrupt. Call rs_ioctl() early to avoid this. * o disable interrupts at the chip level, to force an edge transition * on the 8259 line when interrupts are next enabled and active. * RS232 interrupts are guaranteed to be disabled now by the 8259 * mask, but there used to be trouble if the mask was set without * handling a previous interrupt. */ istop(rs); /* sets modem_ctl_port */ rs_config(rs); sys_outb(rs->int_enab_port, 0); /* Clear any harmful leftover interrupts. An output interrupt is harmless * and will occur when interrupts are enabled anyway. Set up the output * queue using the status from clearing the modem status interrupt. */ sys_inb(rs->line_status_port, &dummy); sys_inb(rs->recv_port, &dummy); rs->ostate = devready(rs) | ORAW | OSWREADY; /* reads modem_ctl_port */ rs->ohead = rs->otail = rs->obuf; /* Enable interrupts for both interrupt controller and device. */ irq = (line & 1) == 0 ? RS232_IRQ : SECONDARY_IRQ; rs->irq = irq; rs->irq_hook_id = rs->irq; /* call back with irq line number */ if (sys_irqsetpolicy(irq, IRQ_REENABLE, &rs->irq_hook_id) != OK) { printf("RS232: Couldn't obtain hook for irq %d\n", irq); } else { if (sys_irqenable(&rs->irq_hook_id) != OK) { printf("RS232: Couldn't enable irq %d (hooked)\n", irq); } } rs_irq_set |= (1 << irq); sys_outb(rs->int_enab_port, IE_LINE_STATUS_CHANGE | IE_MODEM_STATUS_CHANGE | IE_RECEIVER_READY | IE_TRANSMITTER_READY); /* Fill in TTY function hooks. */ tp->tty_devread = rs_read; tp->tty_devwrite = rs_write; tp->tty_echo = rs_echo; tp->tty_icancel = rs_icancel; tp->tty_ocancel = rs_ocancel; tp->tty_ioctl = rs_ioctl; tp->tty_break = rs_break; tp->tty_close = rs_close; /* Tell external device we are ready. */ istart(rs); } /*===========================================================================* * rs_interrupt * *===========================================================================*/ void rs_interrupt(message *m) { unsigned long irq_set; int i; rs232_t *rs; irq_set= m->NOTIFY_ARG; for (i= 0, rs = rs_lines; iirq)) rs232_handler(rs); } } /*===========================================================================* * rs_icancel * *===========================================================================*/ static int rs_icancel(tty_t *tp, int UNUSED(dummy)) { /* Cancel waiting input. */ rs232_t *rs = tp->tty_priv; lock(); rs->icount = 0; rs->itail = rs->ihead; istart(rs); unlock(); return 0; /* dummy */ } /*===========================================================================* * rs_ocancel * *===========================================================================*/ static int rs_ocancel(tty_t *tp, int UNUSED(dummy)) { /* Cancel pending output. */ rs232_t *rs = tp->tty_priv; lock(); rs->ostate &= ~(ODONE | OQUEUED); rs->ocount = 0; rs->otail = rs->ohead; unlock(); return 0; /* dummy */ } /*===========================================================================* * rs_read * *===========================================================================*/ static int rs_read(tty_t *tp, int try) { /* Process characters from the circular input buffer. */ rs232_t *rs = tp->tty_priv; int icount, count, ostate; if (!(tp->tty_termios.c_cflag & CLOCAL)) { if (try) return 1; /* Send a SIGHUP if hangup detected. */ lock(); ostate = rs->ostate; rs->ostate &= ~ODEVHUP; /* save ostate, clear DEVHUP */ unlock(); if (ostate & ODEVHUP) { sigchar(tp, SIGHUP, 1); tp->tty_termios.c_ospeed = B0; /* Disable further I/O. */ return 0; } } if (try) { if (rs->icount > 0) return 1; return 0; } while ((count = rs->icount) > 0) { icount = bufend(rs->ibuf) - rs->itail; if (count > icount) count = icount; /* Perform input processing on (part of) the input buffer. */ if ((count = in_process(tp, rs->itail, count, -1)) == 0) break; lock(); /* protect interrupt sensitive variables */ rs->icount -= count; if (!rs->idevready && rs->icount < RS_ILOWWATER) istart(rs); unlock(); if ((rs->itail += count) == bufend(rs->ibuf)) rs->itail = rs->ibuf; } return 0; } /*===========================================================================* * rs_ostart * *===========================================================================*/ static void rs_ostart(rs232_t *rs) { /* Tell RS232 there is something waiting in the output buffer. */ rs->ostate |= OQUEUED; if (txready(rs)) out_int(rs); } /*===========================================================================* * rs_break * *===========================================================================*/ static int rs_break(tty_t *tp, int UNUSED(dummy)) { /* Generate a break condition by setting the BREAK bit for 0.4 sec. */ rs232_t *rs = tp->tty_priv; u32_t line_controls; sys_inb(rs->line_ctl_port, &line_controls); sys_outb(rs->line_ctl_port, line_controls | LC_BREAK); /* XXX */ /* milli_delay(400); */ /* ouch */ printf("RS232 break\n"); sys_outb(rs->line_ctl_port, line_controls); return 0; /* dummy */ } /*===========================================================================* * rs_close * *===========================================================================*/ static int rs_close(tty_t *tp, int UNUSED(dummy)) { /* The line is closed; optionally hang up. */ rs232_t *rs = tp->tty_priv; if (tp->tty_termios.c_cflag & HUPCL) { sys_outb(rs->modem_ctl_port, MC_OUT2 | MC_RTS); } return 0; /* dummy */ } /* Low level (interrupt) routines. */ /*===========================================================================* * rs232_handler * *===========================================================================*/ static void rs232_handler(struct rs232 *rs) { /* Interrupt hander for RS232. */ while (TRUE) { u32_t v; /* Loop to pick up ALL pending interrupts for device. * This usually just wastes time unless the hardware has a buffer * (and then we have to worry about being stuck in the loop too long). * Unfortunately, some serial cards lock up without this. */ sys_inb(rs->int_id_port, &v); switch (v) { case IS_RECEIVER_READY: in_int(rs); continue; case IS_TRANSMITTER_READY: out_int(rs); continue; case IS_MODEM_STATUS_CHANGE: modem_int(rs); continue; case IS_LINE_STATUS_CHANGE: line_int(rs); continue; } return; } } /*===========================================================================* * in_int * *===========================================================================*/ static void in_int(register rs232_t *rs) /* rs line with input interrupt */ { /* Read the data which just arrived. * If it is the oxoff char, clear OSWREADY, else if OSWREADY was clear, set * it and restart output (any char does this, not just xon). * Put data in the buffer if room, otherwise discard it. * Set a flag for the clock interrupt handler to eventually notify TTY. */ u32_t c; #if 0 /* Enable this if you want serial input in the kernel */ return; #endif sys_inb(rs->recv_port, &c); if (!(rs->ostate & ORAW)) { if (c == rs->oxoff) { rs->ostate &= ~OSWREADY; } else if (!(rs->ostate & OSWREADY)) { rs->ostate |= OSWREADY; if (txready(rs)) out_int(rs); } } if (rs->icount == buflen(rs->ibuf)) { printf("in_int: discarding byte\n"); return; /* input buffer full, discard */ } if (++rs->icount == RS_IHIGHWATER && rs->idevready) istop(rs); *rs->ihead = c; if (++rs->ihead == bufend(rs->ibuf)) rs->ihead = rs->ibuf; if (rs->icount == 1) { rs->tty->tty_events = 1; force_timeout(); } else printf("in_int: icount = %d\n", rs->icount); } /*===========================================================================* * line_int * *===========================================================================*/ static void line_int(register rs232_t *rs) /* rs line with line status interrupt */ { /* Check for and record errors. */ u32_t s; sys_inb(rs->line_status_port, &s); rs->lstatus = s; if (rs->lstatus & LS_FRAMING_ERR) ++rs->framing_errors; if (rs->lstatus & LS_OVERRUN_ERR) ++rs->overrun_errors; if (rs->lstatus & LS_PARITY_ERR) ++rs->parity_errors; if (rs->lstatus & LS_BREAK_INTERRUPT) ++rs->break_interrupts; } /*===========================================================================* * modem_int * *===========================================================================*/ static void modem_int(register rs232_t *rs) /* rs line with modem interrupt */ { /* Get possibly new device-ready status, and clear ODEVREADY if necessary. * If the device just became ready, restart output. */ if (devhup(rs)) { rs->ostate |= ODEVHUP; rs->tty->tty_events = 1; force_timeout(); } if (!devready(rs)) rs->ostate &= ~ODEVREADY; else if (!(rs->ostate & ODEVREADY)) { rs->ostate |= ODEVREADY; if (txready(rs)) out_int(rs); } } /*===========================================================================* * out_int * *===========================================================================*/ static void out_int(register rs232_t *rs) /* rs; line with output interrupt */ { /* If there is output to do and everything is ready, do it (local device is * known ready). * Notify TTY when the buffer goes empty. */ if (rs->ostate >= (ODEVREADY | OQUEUED | OSWREADY)) { /* Bit test allows ORAW and requires the others. */ sys_outb(rs->xmit_port, *rs->otail); if (++rs->otail == bufend(rs->obuf)) rs->otail = rs->obuf; if (--rs->ocount == 0) { rs->ostate ^= (ODONE | OQUEUED); /* ODONE on, OQUEUED off */ rs->tty->tty_events = 1; force_timeout(); } else if (rs->ocount == RS_OLOWWATER) { /* running low? */ rs->tty->tty_events = 1; force_timeout(); } } } #endif /* NR_RS_LINES > 0 */