Difference between revisions of "Geneve logical memory map"

From Ninerpedia
Jump to navigation Jump to search
Line 45: Line 45:
! F118
! F118
| Keyboard
| Keyboard
| Single address F118 with 8 mirrors
|-
|-
! F120
! F120

Revision as of 16:32, 26 January 2021

The logical address map determines which devices or memory areas appear in the logical address space. These are the addresses as seen from the CPU or the program that is run, but they need not correspond to the same physical address at all times. The correspondence is provided by the mapper.

Native mode

The native mode is also called MDOS mode. It is the mode which the Geneve initially boots to, typically with white letters on dark blue, and 80 column display.

Memory map

0000 Reserved Operating system
0400 Free space Onboard memory or expansion
2000
4000
6000
8000
A000
C000
E000
F000 On-chip memory 256 bytes Hides mapped page
F100 Video ports See below
F110 Mapper See link
F118 Keyboard Single address F118 with 8 mirrors
F120 Sound chip
F130 Clock chip
F140 Free space Onboard memory or expansion
F800
FFF8
FFFA Decrementer
FFFC NMI vector
FFFE

Video ports

Decoding: 1111 0001 0000 xpp0 (pp = port number; x = don't care)

Addresses are mirrored at position+8 (F100 = F108,...)

Read Write
F100 (Port 0) VRAM VRAM
F102 (Port 1) Status register Address counter or video register
F104 (Port 2) - Palette register
F106 (Port 3) - Indirect video register access

GPL mode

The GPL mode is the compatibility mode, which is provided to run TI-99/4A programs.

Memory map

0000 GPL interpreter Operating system
2000 Free space 8 KiB Onboard memory or expansion
3000
3FFE
4000 DSR space Normally used by the GeneveOS DSR
6000 Cartridge ROM contents Loaded from disk
8000 Mapper See link
8008 Keyboard
8010 Clock chip
8020 Free space Also includes the "PAD RAM" (16-bit RAM of the TI-99/4A)
8300 Here, its speed depends on SRAM or DRAM mapping
8400 Sound chip
8600 External bus Any device in the PEB that maps to this address
8800 Video ports
9000 Speech synthesizer if plugged into the PEB
9800 GRAM
A000 Free space 24 KiB
C000
E000
F000 On-chip memory Hides mapped page
F100 Free space
FFFA Decrementer
FFFC NMI vector
FFFE

Video ports

Decoding: 1000 1wxx xxxx xpp0 (pp = port number; x = don't care; w = write)

Addresses are mirrored 64 times (8800 = 8810 = 8820 = ... 8BF0)

Read Write
8800 (Port 0) VRAM -
8C00 (Port 0) - VRAM
8802 (Port 1) Status register -
8C02 (Port 1) - Address counter or video register
8C04 (Port 2) - Palette register
8C06 (Port 3) - Indirect video register access