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| <H2><A NAME="s6">6. The console character sets</A></H2> |
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| <P>The kernel first tries to figure out what symbol is meant by any given |
| user byte, and next where this symbol is located in the current font. |
| <P>The kernel knows about 5 translations of bytes into console-screen symbols. |
| In Unicode (UTF-8) mode, the UTF-8 code is just converted directly into |
| Unicode. The assumption is that almost all symbols one needs are present |
| in Unicode, and for the cases where this does not hold the codes |
| 0xf000-0xf1ff are reserved for direct font access. |
| When not in Unicode mode, one of four translation tables is used. |
| The four tables are: a) Latin1 -> Unicode, b) VT100 graphics -> Unicode, |
| c) PC -> Unicode, d) user-defined. |
| <P>There are two character sets, called G0 and G1, and one of them |
| is the current character set. (Initially G0.) |
| Typing Ctrl-N causes G1 to become current, Ctrl-O causes G0 to become current. |
| <P>These variables G0 and G1 point at a translation table, and can be changed |
| by the user. Initially they point at tables a) and b), respectively. |
| The sequences ESC ( B and ESC ( 0 and ESC ( U and ESC ( K cause G0 to point |
| at translation table a), b), c) and d), respectively. |
| The sequences ESC ) B and ESC ) 0 and ESC ) U and ESC ) K cause G1 to point |
| at translation table a), b), c) and d), respectively. |
| <P>The sequence ESC c causes a terminal reset, which is what you want if the |
| screen is all garbled. The oft-advised <CODE>echo ^V^O</CODE> will only |
| make G0 current, but there is no guarantee that G0 points at table a). |
| In some distributions there is a program reset(1) that just does |
| <CODE>echo ^[c</CODE>. |
| If your termcap entry for the console is correct (and has an entry |
| <CODE>:rs=\Ec:</CODE>), then also <CODE>setterm -reset</CODE> will work. |
| <P>The user-defined mapping table can be set using mapscrn(8). |
| The result of the mapping is that if a symbol c is printed, the symbol |
| <CODE>s = map[c]</CODE> is sent to the video memory. The bitmap that corresponds to |
| <CODE>s</CODE> is found in the character ROM, and can be changed using setfont(8). |
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