*==============================================================================*
*                                                                              *
*                        GRAM-CARD ROM ROUTINES                                *
*                                                                              *
* Disassembled and commented by Thierry Nouspikel. Geneva, September 1991      *
*==============================================================================*
 
The 128K Gram-Card contains assembly language and gpl routines stored in rom
memory at addresses >4000 to >5FFF. These routines appear when cru bit 0 is set.
 
Memory structure
----------------
 
>4000 +----------+
      |pwr-up    |       Power-up routine. Copies programs to gram.
      |editmem   |       Memory editor. Executed in this memory.
      |modul     |       Basic program -> module. Executed in this memory.
>4B00 +----------+
      |gpl modul |       Gpl program to start basic "module". Copied to gram.
>4C00 +----------+
      |gpl gram  |       Gpl program: gram card menu. Copied to gram.
>4E00 +----------+
      |loader    |       Loader menu and related routines. Copied to low memory
      |          |       expansion either directly or via gram.
>5FFF +----------+
 
 
 
Here is a summary of the different operations:
 
Power up
--------
Each time you reset the computer, this routine is executed. This occurs after
creating the title screen (home computer...) but before checking for key pressed
 
 
       cpu
>4000 +----+             >6000 +----+
      |run |                   |xxxx|
      |    |             >6200 +----+         ^
>4B00 +----+       +---------> |XXXX|         |
      |    |       |(1)        |XXXX|        (2)
>4C00 +----+       |     >7400 +----+
      |xxxx|       |           | 00 |
>4E00 +----+       |     >7FFF +----+
      |XXXX| ------+
      |XXXX|
>5FFF +----+
 
1) Copies gram header (gramcard >98xx) and assembly routines to gram memory.
   Clears remainding space up to >8000.
   This only happens if there is no module pluged in, neither in the gram card.
2) Exits.
 
 
Gram-card menu
--------------
Here is what happens when you select "gramcard >98xx" from the program menu.
 
 
       cpu                      gram
>2000 +----+             >6000 +----+
      |    |                   |run |
>2700 +----+       (1)   >6200 +----+
      |XXXX| <---------------- |XXXX|
      |XXXX|  (2)              |XXXX|
>3900 +----+             >7400 +----+
      |    |                   | 00 |
>3FFF +----+             >7FFF +----+
 
1) Gpl program displays first menu (loader, dsk1.xb, etc) and alternative menu
   (loader, dsk1.aa, etc). After you selected a valid key, it copies assembly
   language routines to low memory expansion and
2) Branches either to "load file" subroutine (at >27FA) or to loader menu
   subroutine (at >2808).
 
 
Call editmem
------------
This program is executed inside the card rom.
It uses the scratch pab (cpu mem >8300 to >83FF) to store variables and data.
 
 
       cpu
>4000 +----+
      |    |
      |run |
>4B00 +----+
      |    |
>4C00 +----+
      |    |
>4E00 +----+
      |    |
      |    |
>5FFF +----+
 
 
Call modul
----------
This program is also executed inside the card rom.
 
 
       cpu                      gram                    vdp
>4000 +----+             >6000 +----+            >0000 +----+
      |    |      +----------> |xxxx|                  |    |
      |run |      |      >6200 +----+                  |    |
>4B00 +----+      |(2)         |    |                  |    |
      |xxxx| -----+            |    |                  |    |
>4C00 +----+             >7400 +----+                  |    |
      |    |                   |    |                  |    |
>4E00 +----+             >8000 +----+                  |    |
      |    |                   |    |                  |    |
      |    |                   |    |      (1)   +---- |llll|
>5FFF +----+                   |llll| <----------|     |    |
                               |bbbb|            +---- |bbbb|
                         >9FFF +----+            >3FFF +----+
 
1) Copies basic line number table and basic program to gram, from vdp mem.
2) Copies the gpl program that will start module, when selected from program
   menu, and display "press enter to reset" once module execution is over.
 
 
Call gram
---------
 
 
       cpu
>2000 +----+
      |    |
>2700 +----+
      |XXXX| <-----+
      |XXXX| (2)   |
>3900 +----+       |
      |    |       |
>3FFF +----+       |
                   |
                   | (1)
       cpu         |
>4000 +----+       |
      |    |       |
      |run |       |
>4B00 +----+       |
      |    |       |
>4C00 +----+       |
      |    |       |
>4E00 +----+       |
      |XXXX| ------+
      |XXXX|
>5FFF +----+
 
1) Copies assembly language routines to low memory expansion and
2) Executes loader menu subroutine (different entry point: >27FE).