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Add description of memory map to tasker.md
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Philip Zembrod
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@ -140,6 +140,98 @@ of the task's user area will be placed on the stack.
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## Memory map
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The memory used by VolksForth ranges from
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`ORIGIN` to `LIMIT` . Below `ORIGIN` are the
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Kernal variables, the screen memory and a single line of
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BASIC with a `SYS` command that starts VolksForth.
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Beyond `LIMIT` are I/O ports and the Kernal ROM.
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Just below `LIMIT` the block buffers are stored; each with a size
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of 1 Kbyte tall. When the system starts, as many buffers are
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allocated as fit between `R0` and `LIMIT`.
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The rest of the system, located between `ORIGIN` and `RO`, consists of
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two areas. The upper area contains the return stack (growing downwards,
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starting at `RO @`) and the user area (growing upwards, starting at `UP@`).
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The dictionary and the data stack plus the heap occupy the other area.
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Heap and data stack grow downwards, the heap from `UP@` and the data stack
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from `S0 @`.
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When the heap grows, the data stack is automatically moved downwards.
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New words are stored in the dictionary, which is the fastest-growing
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part of the system during compilation. Therefore the system automatically
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checks that dictionary and data stack don't collide.
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The Bootarea finally contains the initial values of the user
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variables, which is copied during the cold start from there into the
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console task's user area.
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#### Overall memory map
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```
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0xFFFF -> ╔════════════════════╗
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║ I/O and ROM ║
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║ (starts at 0x8000, ║
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║ 0x9F00, 0xD000 or ║
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║ 0xFD00 depending ║
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║ on platform) ║
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limit -> ╠════════════════════╣
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║ buffers ║
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first @ -> ╠════════════════════╣
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║ (unused) ║
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r0 @ -> ╠════════════════════╣ ─────
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║ return stack ║ ⋀
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rp@ -> ╠═════════════════|══╣ |
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║ ⋁ ║
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║ free ║ rlen
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║ ⋀ ║
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╠═════════════════|══╣ |
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║ user area ║ ⋁
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up@ -> ╠════════════════════╣ ─────
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║ heap ║ ⋀
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heap -> ╠════════════════════╣ |
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║ (stack underflow) ║
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s0 @ -> ╠════════════════════╣
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║ stack ║
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sp@ -> ╠═════════════════|══╣ slen
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║ ⋁ ║
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║ free ║
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║ ⋀ ║
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here -> ╠═════════════════|══╣
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║ ║
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║ dictionary ║
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║ ║
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╠════════════════════╣ |
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║ boot area ║ ⋁
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origin -> ╠════════════════════╣ ─────
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║ 10 SYS (2064) ║ SYS (4112) on the C16
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╠════════════════════╣
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║ video memory ║
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╠════════════════════╣
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║ Kernal vars ║
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║ 6502 ZP, stack ║
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╚════════════════════╝
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```
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#### 6502 zero page
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The system also uses zero page memory, with the inner interpreter `NEXT`
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and the stack pointers `RP` and `SP`, among others.
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|Label | C64 | C16 | X16 |
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|-------|-------|-------|-------|
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|N |0x0029 |0x0029 |0x0067 |
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|W |0x0021 |0x0021 |0x006F |
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|IP |0x000E |0x000E |0x005C |
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|NEXT |0x0009 |0x0009 |0x0057 |
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|SP |0x0007 |0x0007 |0x0055 |
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|Put A |0x0006 |0x0006 |0x0054 |
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|UP |0x0004 |0x0004 |0x0052 |
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|RP |0x0002 |0x0002 |0x0050 |
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#### Memory map of a task
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```
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r0 @ -> ╔════════════════════╗ ─────
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@ -211,66 +303,6 @@ robin loop consists of
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└ <- <- <- <- <-- <- <- <┘
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```
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#### Overall memory map
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```
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0xFFFF -> ╔════════════════════╗
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║ I/O and ROM ║
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║ (starts at 0x8000, ║
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║ 0x9F00, 0xD000 or ║
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║ 0xFD00 depending ║
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║ on platform) ║
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limit -> ╠════════════════════╣
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║ buffers ║
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first @ -> ╠════════════════════╣
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║ (unused) ║
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r0 @ -> ╠════════════════════╣ ─────
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║ return stack ║ ⋀
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rp@ -> ╠═════════════════|══╣ |
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║ ⋁ ║
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║ free ║ rlen
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║ ⋀ ║
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╠═════════════════|══╣ |
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║ user area ║ ⋁
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up@ -> ╠════════════════════╣ ─────
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║ heap ║ ⋀
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heap -> ╠════════════════════╣ |
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║ (stack underflow) ║
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s0 @ -> ╠════════════════════╣
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║ stack ║
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sp@ -> ╠═════════════════|══╣ slen
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║ ⋁ ║
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║ free ║
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║ ⋀ ║
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here -> ╠═════════════════|══╣
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║ ║
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║ dictionary ║
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║ ║
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╠════════════════════╣ |
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║ boot area ║ ⋁
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origin -> ╠════════════════════╣ ─────
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║ 10 SYS(2064) ║
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╠════════════════════╣
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║ video memory ║
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╠════════════════════╣
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║ Kernal vars ║
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║ 6502 ZP, stack ║
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╚════════════════════╝
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```
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#### 6502 zero page
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|Label | C64 | C16 | X16 |
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|-------|-------|-------|-------|
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|N |0x0029 |0x0029 |0x0067 |
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|W |0x0021 |0x0021 |0x006F |
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|IP |0x000E |0x000E |0x005C |
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|NEXT |0x0009 |0x0009 |0x0057 |
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|SP |0x0007 |0x0007 |0x0055 |
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|Put A |0x0006 |0x0006 |0x0054 |
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|UP |0x0004 |0x0004 |0x0052 |
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|RP |0x0002 |0x0002 |0x0050 |
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## Glossary
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