
6-83
INITIALIZATION
S5935
Byte
Offset
68h
Byte
Length
8
Binary
Value
not used
Description
Example
70h
4
[Expansion
ROM base addr.]
(example shows 32K bytes)
FFFF8001h
74h
8
not used
7Ch
1
[Interrupt line]
0Ch
7Dh
1
[Interrupt pin]
01h
7Eh
1
[Min-Grant]
00h
7Fh
1
[Max_lat]
00h
80h —
application specific
(1FFh), or
(2FFh), or
(3FFh), etc.
Byte checksum, location dependent on value for length field at offset 0002h.
Table 2. PC Compatible Expansion ROM (Continued)
A 16-bit pointer at location 18h of the PC expansion
ROM identifies the start offset of the PCI data struc-
ture. The PCI data structure is shown in Table 3 and
contains various vendor, product, and program evolu-
tions. If a valid external nv memory is identified by
the S5935, the PCI data structure is used to config-
ure the S5935. The PCI data structure is not neces-
sary for this device to operate. If no external nv
memory is implemented, the S5935 boots with the
default configuration values.
Byte
Offset
0h
Byte Binary
Length Value
4
Description
Signature, the ASCII string ‘PCIR’ where ‘P’ is at offset 0,
‘C’ at offset 1, and so on.
Vendor Identification
Device Identification
Pointer to Vital Product Data
PCI Data Structure Length (starts with signature field)
PCI Data Structure Revision (=0 for this definition)
Class Code
Image Length
Revision Level
Code Type
Indicator (bit D7=1 signifies “l(fā)ast image”)
Reserved
‘PCIR’
4h
6h
8h
Ah
Ch
Dh
10h
12h
14h
15h
16h
2
2
2
2
1
3
2
2
1
1
2
var.
var.
var.
var.
var.
var.
var.
var.
var.
var.
0000h
Table 3. PCI Data Structure
Note: If a serial BIOS ROM is used, the access time
for large serial devices should be considered, since it
may cause a lengthy system delay during initializa-
tion. For example, a 2-Kbyte serial device takes
about 1 second to be read. Many systems, even
when BIOS ROMs are ultimately shadowed into sys-
tem RAM, may read this memory space twice (once
to validate its size and checksum, and once to move
it into RAM). Execution directly from a serial BIOS
ROM, although possible, may be unacceptably slow.