The Dandelion Color display - what you need to know to use it Herb Jellinek 6 December 1984 The Dandelion color display is an odd creature. The display framebuffer lives in an IBM PC-compatible chassis, while the framebuffer that Lisp programs manipulate lives in the Lisp address space. Without some sort of special intervention, updates to the Lisp framebuffer will never appear on the color screen. We solved this problem by creating a daemon process that runs many times a second, scanning the Lisp copy of the framebuffer for changes, and transmitting those changes to the outboard framebuffer. We check the dirty bit of each page in the framebuffer; if a page is dirty, we transmit it across the BusMaster interface to the appropriate spot in the remote framebuffer and then mark it as clean; if already clean, we skip it. To ensure that the daemon runs in a timely fashion, it is invoked from Interlisp-D's keyboard interrupt, which happens 77 times per second. The system variable \PERIODIC.INTERRUPT.FREQUENCY specifies how many keyboard interrupts should occur between invocations of the Lisp daemon. A value of 1 means to run the daemon 77 times per second; a value of 77 means to run it once per second. It is reasonable to set it to 10 or so. Another variable, \DDLCOLOR.MOVELIMIT, specifies the maximum number of pages to move per daemon-invocation. Forty (40) is a reasonable value for this, but under no circumstances should it be larger than 250 (the value of ColorScreenBitMapPages).  TIMESROMAN > TIMESROMAN  TIMESROMAN  TIMESROMAN‰ TIMESROMAN GACHA  TIMESROMAN GACHA ¹ TIMESROMAN GACHA  TIMESROMAN ë z¸