Bus

A bus is the hardware used to connect peripheral devices to the computer. SVR5 and SCO OpenServer 5 support a number of industry-standard buses with different performance levels. Various bus standards are compared below.

Supported bus types

 Bus type   Clock speed   Bus width   Bus speed
 (Mhz)      (Mhz)         (bits)      (MB/sec)
 ------------------------------------------------------
 ISA-8      8             8           5 (continuous)
 ISA-16     8             16          10 (continuous)
 EISA       8             32          32 (burst)
 MCA        10            32          40 (burst)
 PCI        33            32          132 (continuous)
 VESA       33            32          132 (continuous)

DDI coding

Use the facilities discussed in ``Autoconfiguration'' to detect and configure devices on any supported bus type. SCO SVR5 1 and 2 and SVR5 support bus-independent APIs for access to for this purpose. bus-dependent configuration space. Specifically:

• To query the bus type, use the CM_BUSBRDTYPE parameter to cm_params(D5).

• To configure generic parameters such as the I/O address and IRQ, use the cm_getval(D3) function, specifying parameters from those listed on the cm_params(D5) manual page.

• For device-specific parameters, use the functions listed in ``Configuration manager''.

• For information about EISA configuration space, see eisa(D4) and eisa_parse_devconfig(D3). For information about PCI configuration space, see pci(D5).

• To add support for a new bus type to the system, use the non-portable si_add_bustype(D3sys) function.

ODDI coding

On SCO OpenServer 5, separate functions are defined for accessing each supported bus type. These include:

archtobus(D3oddi)

extract bus type from architecture; used for ISA, EISA, and MCA architectures.

pci_buspresent(D3oddi)

determine the presence of a PCI bus.

Because a system can have a PCI bus in combination with any other bus type, driver writers must use both functions in drivers that support both PCI and non-PCI cards.