HP OpenVMS systems documentation

Drivers written in C use the ini_fdt_act macro to initialize an FDT entry for an I/O function. This macro uses the DRIVER$INI_FDT_ACT routine. Both the macro and the routine have been enhanced for OpenVMS Alpha Version 7.0.

The format of the macro in releases prior to OpenVMS Alpha Version 7.0 was:

ini_fdt_act (fdt, func, action, bufflag)

where the bufflag parameter must be one of the following:

	BUFFERED	The specified function is buffered.
	NOT_BUFFERED	The specified function is direct. This is a synonym for DIRECT.
	DIRECT	The specified function is direct. This is a synonym for NOT_BUFFERED.

The use of the bufflag parameter has been enhanced to include the declaration of 64-bit support by allowing 3 additional values:

	BUFFERED_64	The specified function is buffered and supports a 64-bit address in the p1 parameter.
	NOT_BUFFERED_64	The specified function is direct and supports a 64-bit address in the p1 parameter.
	DIRECT_64	The specified function is direct and supports a 64-bit address in the p1 parameter.

If a driver does not support a 64-bit address on any of its functions, there is no need to change its use of the ini_fdt_act macro.

For example, the following C code segment declares that the IO$_READVBLK and IO$_READLBLK functions support 64-bit addresses.

ini_fdt_act (&driver$fdt, IO$_SENSEMODE, my_sensemode_fdt, BUFFERED); ini_fdt_act (&driver$fdt, IO$_SETMODE, my_setmode_fdt, BUFFERED); ini_fdt_act (&driver$fdt, IO$_READVBLK, acp_std$readblk, DIRECT_64); ini_fdt_act (&driver$fdt, IO$_READLBLK, acp_std$readblk, DIRECT_64);

The interpretation of the bufflag parameter to the DRIVER$INI_FDT_ACT routine has been enhanced to support the new values and the setting of the 64-bit support mask in the FDT data structure.

4.4.2 Drivers Written in MACRO-32

As of OpenVMS Alpha Version 7.0, drivers written in MACRO-32 use a new FDT_64 macro to declare the set of I/O functions for which the driver supports 64-bit addresses. The use of the FDT_64 macro is similar to the use of the existing FDT_BUF macro. If a driver does not support a 64-bit address on any of its functions, there is no need to use the new FDT_64 macro.

For example, the following MACRO-32 code segment declares that the IO$_READVBLK and IO$_READLBLK functions support 64-bit addresses.

FDT_INI MY_FDT FDT_BUF <SENSEMODE,SETMODE> FDT_64 <READVBLK,READLBLK> FDT_ACT ACP_STD$READBLK, <READVBLK,READLBLK>

4.4.3 Drivers Written in BLISS

As of OpenVMS Alpha Version 7.0, drivers written in BLISS-32 and BLISS-64 use a new optional keyword parameter, FDT_64, to the existing FDTAB macro to declare the set of I/O functions that support 64-bit addresses. The use of the new FDT_64 parameter is similar to the use of the existing FDT_BUF parameter. If a driver does not support a 64-bit address on any of its functions, there is no need to use the new FDT_64 parameter.

For example, the following BLISS code segment declares that the IO$_READVBLK and IO$_READLBLK functions support 64-bit addresses.

FDTAB ( FDT_NAME = MY_FDT, FDT_BUF = (SENSEMODE,SETMODE), FDT_64 = (READVBLK,READLBLK), FDT_ACT = (ACP_STD$READBLK, (READVBLK,READLBLK) ) );

4.5 I/O Mechanisms

Table 4-2 summarizes the I/O mechanisms that support 64-bit addresses.

Table 4-2 Summary of 64-Bit Support by I/O Mechanism

Mechanism	64-Bits	Comments
Simple buffered I/O	Yes	32/64-bit BUFIO packet headers
Complex Buffered I/O	No	Used by XQP and ACPs
Complex Chained Buffered I/O	Yes	New cells in CXB
Direct I/O	Yes	Cross-process PTE problem
LAN VCI	Yes	Cross-process PTE problem
VMS I/O Cache	Yes	64-bit support is transparent to other components
Buffer Objects	Yes	Special case of direct I/O
Diagnostic buffers	Yes	Driver-wide attribute

4.5.1 Simple Buffered I/O

Figure 4-1 shows a 32-bit buffered I/O packet header.

Figure 4-1 32-Bit Buffered I/O Packet Header

• No symbolic offsets currently defined.
• Frequent use of manifest constants; for example:

  MOVAB 12(R2),(R2)

  
  

• Dependencies on the packet header layout can be anywhere in the driver code path.
• Drivers allocate and initialize these packets.

A 64-bit buffered packet header is as shown in Figure 4-2.

Figure 4-2 New 64-Bit Buffered I/O Packet Header

• BUFIO structures and offsets now defined.
• Both 32-bit and 64-bit formats supported.
• BUFIO packets are self-identifying.
• New routines are EXE_STD$ALLOC_BUFIO_64, EXE_STD$ALLOC_BUFIO_32.
• Used for diagnostic buffers as well.