= GIET-VM / TTY Driver =

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The [source:soft/giet_vm/giet_drivers/tty_driver.c tty_driver.c] and [source:soft/giet_vm/giet_drivers/tty_driver.h tty_driver.h] files define the TTY driver. 

This ''vci_multi_tty'' component is a multi-terminals controller. It is an ''external'' peripheral.

The total number of terminals available in the platform must be defined by the configuration  parameter NB_TTY_CHANNELS in the ''hard_config.h'' file.

The kernel terminal is TTY[0]. Private TTY Terminal can be allocated to the task requesting it thanks to the ''giet_tty_alloc()'' system call. The corresponding TTY terminal index is stored in the context of the task.

The SEG_TTY_BASE address must be defined in the hard_config.h file.

The virtual base address of the associated segment is  vbase = SEG_TTY_BASE + cluster_io << 32

The addressable registers map are defined [source:soft/giet_vm/giet_drivers/tty_driver.h here].

== __Access functions__ ==

 === unsigned int '''_tty_get_register'''( unsigned int channel,   unsigned int index ) ===
This low level function returns the value of register (channel / index).

 === void '''_tty_set_register'''( unsigned int channel,  unsigned int index,  unsigned int value ) ===
This low level function set a new value in register (channel / index).

 === void '''_tty_init'''( unsigned int channel ) ===
This low function initialises a TTY channel.

== __Interrupt Service Routines__ ==

 === void '''_tty_rx_isr'''( unsigned int irq_type,  unsigned int irq_id,  unsigned int channel ) ===
This Interrupt Service Routine handles the IRQ signaling that the RX buffer  is not empty. IT can be an HWI or an SWI.
There is one communication buffer _tty_rx_buf[i] and one synchronisation variable _tty_rx_full[i] per channel.
It does nothing if the TTY_RX buffer is empty, or if the kernel buffer is full when the ISR is called.

 === void '''_tty_tx_isr'''( unsigned int irq_type,  unsigned int irq_id,  unsigned int channel ) ===
This Interrupt Service Routine handles the IRQ signaling that the TX buffer is empty. IT can be an HWI or an SWI.
There is one communication buffer _tty_rx_buf[i] and one synchronisation variable _tty_rx_full[i] per channel.
A character is lost if the buffer is full when the ISR is executed.
It is not implemented yet...