System Controller Functions; System Clock Driver; Arbitration Module; Fixed Priority Arbitration Mode (Pri) - Caen V2718 Technical Information Manual

Document type: Title:
User's Manual (MUT) Mod. V2718 VME PCI Optical Link Bridge

2.9. System Controller Functions

When located in Slot 1 of the VME crate, the V2718 assumes the role of SYSTEM
CONTROLLER and sets the SYSTEM CONTROLLER status bit in the STATUS register.
In accordance with the VME64 specification, as SYSTEM CONTROLLER the V2718
provides:
−
a system clock driver,
−
an arbitration module,
−
an IACK Daisy Chain Driver (DCD)
−
a bus timer.

2.9.1. System Clock Driver

The V2718 provides a 16.66 MHz SYSCLK signal when configured as System Controller.

2.9.2. Arbitration Module

When the V2718 is SYSTEM CONTROLLER, the Arbitration Module is enabled. The
Arbitration
Module supports the following arbitration modes:
−

Fixed Priority Arbitration Mode (PRI),

−
Round Robin Arbitration Mode (RRS) (default setting).
These are set with the Arbiter bit in the STATUS register
2.9.2.1.
In this mode, the order of priority is BR[3], BR[2], BR[1], and BR[0] as
defined by the VME64 specification. The Arbitration Module issues a Bus Grant (BGO
[3:0]) to the highest requesting level.
If a Bus Request of higher priority than the current bus owner becomes asserted, the
Arbitration Module asserts BCLR until the owner releases the bus (BBSY is negated).
2.9.2.2.
This mode arbitrates all levels in a round robin mode, repeatedly scanning from levels 3
to 0.
Only one grant is issued per level and one owner is never forced from the bus in favor of
another requester (BCLR is never asserted).
Since only one grant is issued per level on each round robin cycle, several scans will be
required to service a queue of requests at one level.

2.10. Bus Timer

A programmable bus timer allows users to select a VMEbus time-out period. The time-
out period is programmed through the Bus Timeout bit in the Control register ( = 0 →
timeout = 50 µs; = 1 → timeout = 400µs). The VMEbus Timer module asserts BERR if a
VMEbus transaction times out (indicated by one of the VMEbus data strobes remaining
asserted beyond the time-out period).
NPO:
00106/03:V2718.MUTx/11
Fixed Priority Arbitration Mode (PRI)

Round Robin Arbitration Mode (RRS)

Filename:
V2718_REV11.DOC
Revision date: Revision:
03/07/2018 11
Number of pages:
79
Page:
18