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Writing to the console

When a console device is written to, the function con_write gets invoked. This function manages all the control characters and escape sequences used to provide applications with complete screen management. The escape sequences implemented are those of the vt102 terminal; This means that your environment should say TERM=vt102 when you are telnetting to a non- host; the best choice for local activities, however, is TERM=console because the console offers a superset of vt102 functionality.

con_write(), thus, is mostly made up of nested switch statements, used to handle a finite state automaton interpreting escape sequences one character at a time. When in normal mode, the character being printed is written directly to the video memory, using the current attr-ibute. Within console.c, all the fields of struct vc are made accessible through macros, so any reference to (for example) attr, does actually refer to the field in the structure vc_cons[currcons], as long as currcons is the number of the console being referred to.

Actual mapping and unmapping of the console memory to screen is performed by the functions set_scrmem() (which copies data from the console buffer to video memory) and get_scrmem (which copies back data to the console buffer). The private buffer of the current console is physically mapped on the actual video RAM, in order to minimize the number of data transfers. This means that get- and set- -_scrmem() are static to console.c and are called only during a console switch.



Converted on:
Mon Apr 1 10:20:16 EST 1996