linux设备模型之uart驱动架构分析

circ = state->info->xmit;

if (!circ->buf)

return 0;

spin_lock_irqsave(port->lock, flags);

while (1) {

c = CIRC_SPACE_TO_END(circ->head, circ->tail, UART_XMIT_SIZE);

if (count c)

c = count;

if (c = 0)

break;

memcpy(circ->buf + circ->head, buf, c);

circ->head = (circ->head + c) (UART_XMIT_SIZE - 1);

buf += c;

count -= c;

ret += c;

}

spin_unlock_irqrestore(port->lock, flags);

uart_start(tty);

return ret;

}

Uart_start()代码如下：

static void uart_start(struct tty_struct *tty)

{

struct uart_state *state = tty->driver_data;

struct uart_port *port = state->port;

unsigned long flags;

spin_lock_irqsave(port->lock, flags);

__uart_start(tty);

spin_unlock_irqrestore(port->lock, flags);

}

static void __uart_start(struct tty_struct *tty)

{

struct uart_state *state = tty->driver_data;

struct uart_port *port = state->port;

if (!uart_circ_empty(state->info->xmit) state->info->xmit.buf

!tty->stopped !tty->hw_stopped)

port->ops->start_tx(port);

}

显然，对于write操作而言，它就是将数据copy到环形缓存区。然后调用port->ops->start_tx()将数据写到硬件寄存器。

八：Read操作

Uart的read操作同Tty的read操作相同，即都是调用ldsic->read()读取read_buf中的内容。有对这部份内容不太清楚的，参阅《 linux设备模型之tty驱动架构》.

九：小结

本小节是分析serial驱动的基础。在理解了tty驱动架构之后，再来理解uart驱动架构应该不是很难。随着我们在linux设备驱动分析的深入，越来越深刻的体会到，linux的设备驱动架构很多都是相通的。只要深刻理解了一种驱动架构。举一反三。也就很容易分析出其它架构的驱动了。