OSDev.org

Posted: **Tue Aug 05, 2008 6:18 pm**

I have an idea for a portable driver interface but would like feedback and direction on its development. I know UDI and EDI already exist but they dont fit the simpler design I like.

The basic idea is each driver is written as a relocatable binary, the file format is yet to be defined but ELF is a standard that might handle the loading/relocation. The entry point in the header is always to initdevice.

In general a pdi driver is written with all its supported functions passed to the OS in a device ops struct. A native OS driver acts as a wrapper to the pdi functions. Any functions not suported by the OS are ignored, any functions that an OS requires are included in a specific version. If the function is not handled by the driver the OS either drops back its function support or unloads the driver. A minimum amount of library support is included in the kernel.

The interface is designed for asm using ecx as a parameter count and edx as a pointer to the parameters. C drivers will need a save these values to use the parameters.

An example driver for vga is shown below.

pdi_vga.c

Code: Select all

struct videoop{
	// required for every device
	int opversion;			// driver operations version
	int (*initdevice)(void)		// initializes the device
	int (*resetdevice)(void)	// resets the device
	int (*enddevice)(void)		// stops the device
	int (*deviceinfo)(void)		// info about the device

	// device specific
	int (*setmode)(void)		// sets the video mode
	int (*getmode)(void)		// gets the video mode
	int (*gotoxy)(void)		// set cursor position
	int (*getxy)(void)		// get cursor position
	int (*putchar)(void)		// writes a character
	int (*getchar)(void)		// reads a character
	int (*putpixel)(void)		// puts a pixel
	int (*getpixel)(void)		// gets a pixel

	// svga/3d acceleration goes here in an extended version
};

#define	VGA_OP_VERSION	1

struct videoop vgaops={
	.opversion=VGA_OP_VERSION,
	.initdevice=initvga,
	.resetdevice=resetvga,
	.enddevice=endvga,
	.deviceinfo=infovga,
	.setmode=setmode,
	.getmode=getmode,
	.gotoxy=gotoxy,
	.getxy=getxy,
	.putchar=putchar,
	.getchar=getchar,
	.putpixel=putpixel,
	.getpixel=getpixel
};

int initvga(void)
{
	int argc,*argv;
	int ver;

	asm(
		mov	[argc],ecx
		mov	[argv],edx
	);
	
	if(!argc){
		return -1;	// no version number
	}

	ver=*argv[0];		// required version of videoop for OS
	if(ver>VGA_OP_VERSION){
		return -1;	// unsupported version
	}
	
	asm(
		mov	edx,&vgaops	// return vgaops in edx
	);
	return 0;
}

int setmode(void)
{
	int argc,*argv;
	int mode;

	asm(
		mov	[argc],ecx
		mov	[argv],edx
	);

	if(!argc){
		return -1;	// no mode number
	}

	return writeregs(mode);
}

and the OS specific driver

vgadrv.c

Code: Select all

struct videoops *vgaops;

struct videoops *initvga(int ver)
{
	struct videoops *ops;
	int (*initdevice)(void);
	
	initdevice=pdi_vga_entry;	// entry point in driver file
	asm(
		mov	edx,&ver
		mov	ecx,1
	);
	initdevice();
	asm(
		mov	[ops],edx
	);
	return ops;
}

int driver_init(...)
{
	load("pdi_vga.drv");
	vgaops=initvga(1,1);	// initdevice vgaops version 1 required
	setmode(T80x25x16);	// set display to a known mode
	return 0;
}

int setmode(int mode)
{
	asm(
		mov	edx,&mode
		mov	ecx,1
	);
	return vgaops->setmode();
}

This just the simple version to give you an idea. Id like to know if this is something useful or interesting to other OSdevers or not. Thanks.

Posted: **Tue Aug 05, 2008 9:41 pm**

Hi,

b.zaar wrote:I know UDI and EDI already exist but they dont fit the simpler design I like.

That's exactly the problem with portable/universal device driver interface ideas - they don't fit the design/s other people like; so they don't get used by other people (which would probably make it the same as a native device driver interface for your OS only, regardless of whether you call it "portable" or not)....

Cheers,

Brendan

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