1. Functional Description
28
Tsi308 User Manual
80D4000_MA001_02
Tundra Semiconductor Corporation
www.tundra.com
1.7
Clocking
During functional operation, the Tsi308’s reference clocks (P0_CLK and P1_CLK) come from
respective PCI-X bus clocks. These clocks are received from same sources that drive clocks to
devices on the bridge’s PCI-X buses and are nominally in phase with them; although they may
be delayed relative to other PCI-X bus clocks. The P1_CLK is only used to clock the PCI-X
interface logic of second PCI-X port (PCI_B) while the device is operating in split bus mode.
The reference clock frequencies and bus mode (traditional PCI or PCI-X) are indicated by
Px_M66EN, Px_PCIX_N and Px_133_N input pins where x denotes PCI-X bus (0 for PCI_A
and 1 for PCI_B). The Px_PCIX_N and Px_133_N are normal TTL level signals derived from
standard 3-state add-in card connector pin PCIXCAP. Since Tsi308 does not decode PCIXCAP,
user has to implement an external three-level Comparator circuitry to generate Px_PCIX_N and
Px_133_N. A reference circuit can be found in [3]. Though three pins above indicate operating
mode (PCI or PCI-X) and frequency group (33MHz or 66 MHz or 133 MHz), Tsi308 needs
exact operating frequency of a given bus to generate internal clocks as well as to generate PCI-X
Initialization Pattern for devices on PCI-X bus as specified in [3]. This is done through
hardware straps. These straps are sampled using combinational logic while warm/cold reset is in
progress and used to combinationally generate PCI-X initialization pattern that is sampled by
devices on PCI-X bus at the rising edge of PCI reset. Refer Chapter 4 for more details on
Clocking and Hardware strap settings.
1.8
Reset
All the internal resets of Tsi308 and resets for secondary PCI-X ports are derived from
HyperTransport PWROK and RESET# signals. The combination of these two signals defines
ColdReset and WarmReset windows on HyperTransport chain. While PWROK is implemented
as input-only, RESET# is implemented as in-out in Tsi308. The asserted state of RESET# is
stretched by Tsi308 and released after internal PLLs are locked. The PCI-X and CORE PLLs are
only reset upon ColdReset but WarmReset resets HyperTransport PLLs. This way software
could re-program link frequencies and issue WarmReset for new frequencies to take effect.
Содержание TSI308
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Страница 187: ...4 Register Descriptions 187 Tsi308 User Manual 80D4000_MA001_02 Tundra Semiconductor Corporation www tundra com ...
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