This page (revision-270) was last changed on 26-Mar-2023 02:03 by Administrator 

This page was created on 20-Feb-2010 19:16 by Carsten Strotmann

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Version Date Modified Size Author Changes ... Change note
270 26-Mar-2023 02:03 17 KB Administrator to previous
269 26-Mar-2023 02:02 17 KB Administrator to previous | to last
268 26-Mar-2023 02:01 17 KB Administrator to previous | to last
267 26-Mar-2023 02:00 17 KB Administrator to previous | to last ACTION Source Code ==> Action Source Code
266 26-Mar-2023 01:59 17 KB Administrator to previous | to last
265 26-Mar-2023 01:58 17 KB Administrator to previous | to last
264 26-Mar-2023 01:56 17 KB Administrator to previous | to last Remove links to delete manual pages
263 26-Mar-2023 01:22 17 KB Administrator to previous | to last Fix SF links
262 26-Mar-2023 01:21 17 KB Administrator to previous | to last
261 26-Mar-2023 01:18 17 KB Administrator to previous | to last Move manuals to Sourceforge

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At line 9 changed one line
Action! uses a greatly cut-down version of the ALGOL syntax, and thus bears strong similarities with [Pascal] and [C]. Like those languages, Action! is procedural, with programs essentially consisting of a large collection of functions that call each other. It lacked encapsulation or data hiding, but that is not a serious concern in the limited program sizes available on an 8-bit machine. Syntactically it looks very similar to Pascal, with the exception that it uses ALGOL68 DO/OD style bracketing rather than Pascal's BEGIN/END.
Action! uses a greatly cut-down version of the ALGOL syntax, and thus bears strong similarities with [Pascal] and [C]. Like those languages, Action! is procedural, with programs essentially consisting of a large collection of functions that call each other. It lacked encapsulation or data hiding, but that is not a serious concern in the limited program sizes available on an 8-bit machine. Additionally, variables were assigned locally, not on a stack, so recursion was not supported internally. Syntactically it looks very similar to Pascal, with the exception that it uses ALGOL 68 DO/OD style bracketing rather than Pascal's BEGIN/END.
At line 11 changed one line
Action! included a number of features to allow it to run as fast as possible. Notably, it's main data types were BYTE, INT and CARD, 8-bit and 16-bit signed and unsigned values, respectively. These map directly onto the basic 6502-types. The language also included a syntax to directly refer to these objects in memory so they could be mapped into hardware registers. For instance, one could set a variable to "BYTE RTCLOK=20" which defined the 8-bit value at memory location 20 to be the value of the real-time clock. The user could then read that register using the name "RTCLOK".
Action! included a number of features to allow it to run as fast as possible. Notably, it's main data types were BYTE, INT and CARD, 8-bit and 16-bit signed and unsigned values, respectively. These map directly onto the basic 6502-types. The language also included a syntax to directly refer to these objects in memory so they could be mapped into hardware registers. For instance, one could set a variable to {{BYTE RTCLOK=20}} which defined the 8-bit value at memory location 20 to be the value of the real-time clock. The user could then read that register using the name {{RTCLOK}}.
At line 51 changed one line
There is a clever trick in this code. Note that {{RTCLOK}} is defined as a {{BYTE}} but {{TIME}} is defined as a {{CARD}}, a 16-bit value. This is because the clock value is stored in three bytes, 18, 19 and 20. By defining {{TIME}} as a {{CARD}}, when that value is read it automatically reads two bytes, thereby getting a value from both 20 and 19, which provides a value from 0 to 65535 jiffies, about 36 minutes. This is much easier than doing the math in the code.
There is a clever trick in this code. Note that {{RTCLOK}} is defined as a {{BYTE}} but {{TIME}} is defined as a {{CARD}}, a 16-bit value. This is because the clock value is stored in three bytes, 18, 19 and 20. By defining {{TIME}} as a {{CARD}}, when that value is read it automatically reads two bytes, thereby getting a value from both 20 and 19, which provides a value from 0 to 65535 jiffies, about 36 minutes. This avoids the need to read two bytes and manipulate them into a 16-bit value, something that is commonly found in BASIC programs.
This page (revision-270) was last changed on 26-Mar-2023 02:03 by Administrator  Top