6. Arbitration
141
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
6.2.2
Bus Parking
The PowerSpan II PCI arbiter provides a flexible address bus parking scheme. When no master is
requesting the address bus, the PCI arbiter can park on either the:
•
last bus master
•
specific bus master
The bus parking mode is determined by PARK bit in the Px_ARB_CTRL register. When Specific
Master mode is selected by setting the PARK bit to 0, the BM_PARK[2:0] field selects the specific bus
master for bus parking. The parked master must enable its drivers for the following PCI signals:
•
AD[31:0]
•
Px_C/BE#[3:0]
•
PAR
Bus parking does not occur until the PCI bus is idle. When a PCI master is accessing the bus when no
Px_REQ# signals are asserted to the PowerSpan II PCI arbiter, Px_GNT# remains asserted to the
master until the bus becomes idle.
6.2.2.1
Bus Parking on a Non-functioning Master
It is possible for PowerSpan II to park the bus on a master that is considered non-functioning or to park
the bus on the last master that has a status that has changed to non-functioning by the STATUS bit is set
to 1 in the
“PCI-1 Bus Arbiter Control Register” on page 284
. Refer to
Non-functioning PCI Masters” on page 139
for a detailed description of functioning and
non-functioning PCI Masters.
When PowerSpan II parks the bus on a non-functioning PCI Master, the
PowerSpan II PCI
x
Arbiter waits for another master to request the bus. Once another master request the
bus the PCI
x
Arbiter then ignores the non-functioning master until the master is considered
functioning. The master status is considered functioning after PowerSpan II is reset (default setting) or
the STATUS bit is cleared.
6.3
Processor Bus Arbitration
PowerSpan II’s internal processor bus arbiter is enabled through a power-up option
(PWRUP_PB_ARB_EN, see
“Resets, Clocks and Power-up Options” on page 167
). When the internal
arbiter is enabled, PowerSpan II’s PB Master uses an internal arbitration mechanism to acquire the
processor bus. When the internal arbiter is disabled an external arbiter is implemented. The PB Master
uses Address Bus Request (PB_BR[1]_), Address Bus Grant (PB_BG[1]_) and Data Bus Grant
(PB_DBG[1]_) to gain external bus ownership.
PowerSpan II’s internal processor bus arbiter supports three external processor bus masters and
implements internal request and grant lines for the PowerSpan II itself
—
four processor bus masters in
total. The external masters are enabled with the External Master x Enable (Mx_EN) bits in the
“Processor Bus Arbiter Control Register” on page 307
.