Thursday, June 10, 2010

LDD3 notes: TTY

My notes while reading Linux Device Drivers 3rd edition, TTY drivers.

TTY drivers are a generic implementation of a serial port interface with loose coupling of hardware access and data formatting.

It is a char device composed of
  • tty core for user space char device interface
  • line discipline for data formatting
  • tty driver for hardware access

  • can be called from interrupt context.
  • must succeed for single byte write
write buffer treatment
  • put_char, flush_chars - start sending them, return right away
  • wait_until_sent - start sending, wait until done or timeout
  • flush_buffer - discard write buffered chars.


tty_insert_flip_char() for each char

  • whenever count reaches size
  • at the end of sequence

  • 38400,8n1 -style serial settings
  • handshake mechanism selection

  • access control lines
  • tty driver first, except break
  • fallback to inherit core functionality with -ENOICTLCMD
  • Get Line Status Register LSR: data, overrun, parity, framing, break...
  • Wait on MSR: change in CTS,DSR, ring, carrier..

  • rx flow control

  • tx enable/disable
write_wait queue - tty driver wakes up

tty open/close count example? what happens to tty filps on fork?

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