[mark_k]

To get DPMS blanking to work in AmigaOS I think you'd need the monitor driver to support it (poking custom registers from a user program is probably not a good idea...).

If you want to experiment, you can boot the Aminet Debian HDF. Log in as root, then quit X by typing /etc/init.d/xdm stop
Log in as root then run this command: setterm -blank 1 -powersave hsync -powerdown 2

After a minute of inactivity horizontal sync signals are disabled. WinUAE log says:

PAL mode dblscan V=55.3710Hz H=31113.1140Hz (114x561+1) IDX=10 (PAL) D=1 RTG=0
P96FREQ: 561*55.3710 = 31063.1579 / 55.4 = 561
BEAMCON0=5BB6 VTOTAL=0230  HTOTAL=0071
  HSSTOP=0074 HBSTRT=0001  HBSTOP=0023
  VSSTOP=000E VBSTRT=0230  VBSTOP=0030
  HSSTRT=0074 VSSTRT=000C HCENTER=0045
PAL mode dblscan V=55.3710Hz H=31113.1140Hz (114x561+1) IDX=10 (PAL) D=1 RTG=0
P96FREQ: 561*55.3710 = 31063.1579 / 55.4 = 561

After another couple of minutes:

BEAMCON0=5BB6 VTOTAL=0230  HTOTAL=0071
  HSSTOP=0074 HBSTRT=0001  HBSTOP=0023
  VSSTOP=000E VBSTRT=0230  VBSTOP=0030
  HSSTRT=0074 VSSTRT=0233 HCENTER=0045
BEAMCON0=5BB6 VTOTAL=0230  HTOTAL=0071
  HSSTOP=0074 HBSTRT=0001  HBSTOP=0023
  VSSTOP=0233 VBSTRT=0230  VBSTOP=0030
  HSSTRT=0074 VSSTRT=0233 HCENTER=0045
BEAMCON0=5BB6 VTOTAL=0230  HTOTAL=0071
  HSSTOP=0074 HBSTRT=0001  HBSTOP=0023
  VSSTOP=0233 VBSTRT=0230  VBSTOP=0030
  HSSTRT=0074 VSSTRT=0233 HCENTER=0045
Buffer size (656*1) Native
D3D9Ex: working texture allocated pre 656*1, post 768*576, bits per pixel 16
D3D9Ex: 656*1 texture allocated, bits per pixel 16
PAL mode dblscan V=55.3710Hz H=31113.1140Hz (114x561+1) IDX=10 (PAL) D=1 RTG=0
P96FREQ: 561*55.3710 = 31063.1579 / 55.4 = 561
POS (0 0 768 576) - (-56 -287 712 289)[768,576] (0 0)
BEAMCON0=5BB6 VTOTAL=0230  HTOTAL=0071
  HSSTOP=0074 HBSTRT=0001  HBSTOP=0023
  VSSTOP=0233 VBSTRT=0230  VBSTOP=0030
  HSSTRT=0074 VSSTRT=0233 HCENTER=0045
PAL mode dblscan V=55.3710Hz H=31113.1140Hz (114x561+1) IDX=10 (PAL) D=1 RTG=0
P96FREQ: 561*55.3710 = 31063.1579 / 55.4 = 561