GraphicsV
Programmer's Reference Manuals
» Part 1 - Introduction
» Vectors
» Software Vector Numbers
» GraphicsV
Graphics Vector (42)
| Entry | |
|---|---|
| R4 | Bits 0-23: Reason Code |
| Bits 24-31: Driver number | |
| Other registers dependant on call | |
Use
This vector is used by the RISC OS 5 kernel to communicate with the video driver.
User software should always aim to use the appropriate OS SWI instead of calling GraphicsV directly. The information presented here is mainly of use to OS maintainers and video driver developers.
R4 is used by all GraphicsV calls to store both the reason code and to indicate whether the call has been claimed (i.e. acted upon by a driver). When a driver claims a call it will set R4 to zero. By checking R4 after calling GraphicsV it is possible to determine whether the driver supports that call or not.
Reason Codes
| # | |
|---|---|
| 0 | Null reason code for when vector has been claimed |
| 1 | VSync interrupt occurred |
| 2 | Set mode |
| 3 | Set interlace |
| 4 | Set blank |
| 5 | Update pointer |
| 6 | Set DAG |
| 7 | Vet mode |
| 8 | Features |
| 9 | Framestore information |
| 10 | Write palette entry |
| 11 | Write palette entries |
| 12 | Read palette entry |
| 13 | Render |
| 14 | IIC op |
| 15 | Select head |
| 16 | Select startup mode |
| 17 | List pixel formats |
Notes
GraphicsV based video drivers should perform the following sequence of events on startup:
- Call OS_ScreenMode 64 to request a driver number
- Store the number, for use by their GraphicsV handler
- Call OS_Claim to install their GraphicsV handler
- Start generating VSync calls if possible
- Perform any other initialisation that’s required to prepare the driver/hardware
- Call OS_ScreenMode 65 to let the OS know that the driver is ready for use
Once OS_ScreenMode 65 is called the driver should expect to start receiving GraphicsV calls from the OS and from other software. Before that point no calls should be received, and if they are then it’s a bug in someone else’s code and not yours.
On shutdown drivers should use the following sequence:
- Call OS_ScreenMode 66 to indicate that the driver is stopping. Once this call returns the driver should no longer receive GraphicsV calls.
- Halt generation of VSync calls
- Call OS_Release to release the GraphicsV handler
- Call OS_ScreenMode 67 to release the driver number and allow it to be allocated for use by other drivers.
See also HAL Video API for details on how the OS translates GraphicsV calls to HAL calls for systems which contain a video driver in their HAL.
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