Memory map

All services of the ATW800/2 are memory mapped. So, reading/writing to a specific address in memory, you can e.g. communicate with the Transputer(s) or draw to the screen. This is the memory map depending on the Atari system used

As of April 2025

ATW800/2	Mega-ST	Mega-STe	TT
VidMem	0xC00000	0xA00000	0xFEC00000
SharedMem	0xDF4000	0xBF4000	0xFEDF4000
ATWinfo	0xDFDC00	0xBFDC00	0xFEDFDC00
CLUT shadow	0xDFDE00	0xBFDE00	0xFEDFDE00
VDI caches	0xDFE000	0xBFE000	0xFEDFE000
FPGA LUT	0xDFF000	0xBFF000	0xFEDFF000
FPGA Info	0xDFF200	0xBFF200	0xFEDFF200
FPGA VTG	0xDFF800	0xBFF800	0xFEDFF800
FPGA Blit	0xDFF900	0xBFF900	0xFEDFF900
FPGA link	0xDFFAC0	0xBFFAC0	0xFEDFFAC0
C011 Link	0xFFFAC0	0xDFFA80	0xFEFFFAC0
CPLD version	0xFFFAD8	0xDFFA98	0xFEFFFAD8

VidMem

This is where ATW800/2’s video memory starts. For the default firmware, this covers a range of 2 megabytes.

SharedMem

Serves for fast data exchange between Atari and the synthetic Transputer in parallel operation.

ATWInfo

An info structure, created by NVDI/XVDI. Helios, for example, can use it to calculate its video RAM or to exit a Transputer program in an orderly manner.

struct nanoxk_atwinfo {
  long kennung_a;       /*[0] 'ATW8'      -> 0x41545738  */
  long kennung_b;       /*[4] 'XVDI'      -> 0x58564449 / 'NVDI' -> 0x4E564449  */
  long version;         /*[8]  z.B '0100' -> 0x30313030 , struct version, *NOT* VDI-version */
  long version_fpga;    /*[12] z.B '0106' -> 0x30313036  */
  long vdi_memstart;    /*[16] Startaddress videomem for VDI  */
  long vdi_memsize;     /*[20] Videomemory used by Atari, often vdi_stride * vdi_height * byteperpixel  */
  int  vdi_vstride;     /*[24] # of bytes per line  */
  int  vdi_bpp;         /*[26] bit per pixel 1(monochrome), 8, 15, 16  */
  int  vdi_width;       /*[28] width used by VDI */
  int  vdi_height;      /*[30] hight used by VDI */
  int  vtg[16];         /*[32] shadow VTG register, as set by VDI - used for re-init after running a Transputer program */
  int  endmagic;        /*[64] currently 0x4711 - prevents using corrupted data */
  int  stuffing         /*[66] alignment to 32-Bit, currently also 0x4711 */
  /* everything else until byte 511 is currently reserved */
 };

CLUT shadow

This contains a shadow of the VDI color look-up table (CLUT). It needs to be kept up-to-date by the VDI. It’s important if the Transputer is used e.g as an accelerator for the Atari.

VDI caches

This can be used for e.g. fill patterns for VDI acceleration - currently only used by XVDI - total size: 4kB

FPGA LUT / VTG / Blit

These addresses provide means to control the video-output.

FPGA Link / C011 Link

These are the addresses which can be used to communicate with the virtual Transputer inside the FPGA or a real Transputer(s) plugged into the ATW800/2 TRAM sockets.

FPGA Info / CPLD Version

These addresses return information about the currently programmed firmware inside the FPGA and CPLD.