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Shell memory layout
Since QNICE does not offer a dynamic memory management system, the Shell uses a hard-coded memory layout to perform its duties. This memory layout seeks a balance between three conflictive goals:
- When using the Shell's "File Browser" to browse for files (such as games, programs, ROMs, cartridges, etc.): Display as many files and subfolders within a given folder as possible. The memory is needed for displaying the directory entries in an alphabetically ordered fashion.
- When browsing through deeply structured libraries of files, make sure that the file browser remembers all the subfolders so that as soon as you start to "climb up" the directory-tree again (i.e. leave a subdirectory) the file-browser continues where you left off.
- Have an On Screen Menu with as many menu items and sub-menus as possible.
You can configure the memory layout in m2m-rom.asm. Go to the section that is called Heap and Stack
and locate the following constants:
Constant | Meaning |
---|---|
MENU_HEAP_SIZE | Amount of heap reserved for the On Screen Menu, i.e. above-mentioned case (3). This memory amount includes the sum of all characters of all menu and sub-menu items, including buffers for replacing the %s in certain menu items. Since it is hard to guess the correct value for MENU_HEAP_SIZE , the M2M framework outputs valuable debug information on the serial debug console when you press the Help key for the first time. |
HEAP_SIZE | Amount of memory reserved for the above-mentioned case (1): All file- and directory names in the current directory, alphabetically sorted. If your core uses disk images, CRT/ROM images and similar items that need a file browser: Try to maximize this value. |
STACK_SIZE | Overall stack size. System stack = Overall stack size minus B_STACK_SIZE. Needs to be at least 768 words. |
B_STACK_SIZE | Stack used for case (2), i.e. for remembering the sub-folder "climbing path" that a user went but also for replacing filenames that are too long by a shortened filename that ends with ... . For this string replacement an amount of words that equals the maximum screen width is needed plus zero terminator. Additionally B_STACK_SIZE needs 2+<maximum recursive folder climbing depth> words. |
Here is an example log out from the "C64 for MEGA65" core version 5:
Maximum available QNICE memory: 31994
Used as general heap: 28544
Used as menu heap: 1664
Used as stack: 1536
Used as general stack: 768
Used as browser stack: 768
Free QNICE memory: 250
Free space in QNICE ROM: 5631
OSM heap utilization:
MENU_HEAP_SIZE: 1664
Free menu heap space: 260
OPTM_HEAP_SIZE: 260
Free OPTM heap space: 17
The value "Free OPTM heap space" is an indicator for you how you need to size MENU_HEAP_SIZE
. If this value starts to shrink towards zero due to you adding more menu items to config.vhd
it is time to increase MENU_HEAP_SIZE
in m2m-rom.asm. When doing so, make sure that you are decreasing either HEAP_SIZE
or STACK_SIZE
(or both) by the same absolute value that you are increasing MENU_HEAP_SIZE
. Also make sure that you adjust the comments in m2m-rom.asm to match your new values; otherwise you or the reader of your source will be confused later.