If the sequence is valid the first parameter found in the escape sequence or

If the sequence is valid the first parameter found in

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control sequence introducer currently recognized by MINIX 3. If the sequence is valid, the first parameter found in the escape sequence, or zero if no numeric parameter was entered, is assigned to value (line 16380). If the sequence is invalid, nothing happens except that the large switch that ensues (lines 16381 to 16586) is skipped and the escape state is reset to zero before returning from do_escape. In the more interesting case that the sequence is valid, the switch is entered. We will not discuss all the cases; we will just note several that are representative of the types of actions governed by escape sequences. The first five sequences are generated, with no numeric arguments, by the four "arrow" keys and the Home key on the IBM PC keyboard. The first two, ESC [A and ESC [B, are similar to ESC M, except they can accept a numeric parameter and move up and down by more than one line, and they do not scroll the screen if the parameter specifies a move
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that exceeds the bounds of the screen. In such cases, flush catches requests to move out of bounds and limits the move to the last row or the first row, as appropriate. The next two sequences, ESC [C and ESC [D, which move the cursor right and left, are similarly limited by flush. When generated by the "arrow" keys there is no numeric argument, and thus the default movement of one line or column occurs. ESC [H can take two numeric parameters, for instance, ESC [20;60H. The parameters specify an absolute position rather than one relative to the current position and are converted from 1-based numbers to 0-based numbers for proper interpretation. The Home key generates the default (no parameters) sequence which moves the cursor to position (1, 1). ESC [s J and ESC [s K clear a part of either the entire screen or the current line, depending upon the parameter that is entered. In each case a count of characters is calculated. For instance, for ESC [1J, count gets the number of characters from the start of the screen to the cursor position, and the count and a position parameter, dst, which may be the start of the screen, cons->c_org, or the current cursor position, cons->c_cur, are used as parameters to a call to mem_vid_copy. This procedure is called with a parameter that causes it to fill the specified region with the current background color. The next four sequences insert and delete lines and spaces at the cursor position, and their actions do not require detailed explanation. The last case, ESC [n m (note the n represents a numeric parameter, but the "m" is a literal character) has its effect upon cons->c_attr, the attribute byte that is interleaved between the character codes when they are written to video memory. The next function, set_6845 (line 16594), is used whenever it is necessary to update the video controller chip. The 6845 has internal 16-bit registers that are programmed 8 bits at a time, and writing a single register requires four I/O port write operations. These are carried out by setting up an array (vector) of (port, value) pairs and invoking a sys_voutb kernel call to get the system task to do the I/O. Some of the registers of the 6845 video controller chip are shown in Fig. 3-45
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