Page "OS_Byte CMOS 140" does not exist. Please create it now, or hit the "back" button in your browser.
HAL_Video_SetDAG
Hardware Abstraction Layer
HAL entry points from RISC OS
ยป HAL_Video_SetDAG
HAL_Video_SetDAG
(HAL entry #47)
void HAL_Video_SetDAG(uint DAG, uint paddr)
| Entry | |
|---|---|
| DAG | 0 = Set start address of current video display |
| 1 = Set start address of total video buffer | |
| 2 = Set end address (exclusive) of total video buffer | |
| 3 = Set start address of VDU buffer (i.e. as set by OS_Byte 112) | |
| All other values reserved | |
| paddr | Physical address for given DAG |
| Exit | |
|---|---|
| - |
Use
This is an internal call for OS use only and should not be used by user software. User software should use GraphicsV? instead of interacting with the HAL directly.
The OS has a video buffer which is >= total display size, and may be using bank switching (several display buffers) or hardware scroll within the total video buffer.
- DAG=1 will be start address of current total video buffer
- DAG=2 will be end address (exclusive) of current total video buffer
- DAG=0 will be start address in buffer for current display
HALs should respond differently depending on whether hardware scroll is supported or not. (The OS will already know this from HAL_Video_Features).
No hardware scroll
Only DAG=0 is significant, and the end address of the current display is implied by the size of the current mode. Calls with DAG=1,2 should be ignored.
Hardware scroll
DAG=0 again defines display start. DAG=2 defines the last address (exclusive) that should be displayed before wrapping back (if reached within display size), and DAG=1 defines the address to which accesses should wrap back.