6. Arbitration
142
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
The processor bus arbiter implements two levels of priority. Devices programmed into a specific
priority level operate in a round robin fashion. Each master has a External Master x Priority Level
(Mx_PRI) bit in the PB_ARB_CTRL register to determine its arbitration level for the address bus. The
arbitration level for each master can be reconfigured during system run-time.
6.3.1
Address Bus Arbitration
The PB_BG_ pins change state under the following conditions:
•
The assertion of PB_REQ_ when the bus is idle.
•
After the assertion of PB Address Acknowledge (PB_AACK_), Bus Grant (PB_BG_) changes to
the next requesting master or the parked master.
Some host processors (for example, the PowerQUICC II) and other processor bus agents require the
system signal ABB_ to qualify address bus grants. The PowerSpan II PB Master Interface does not
require ABB_ to qualify data bus grants.
6.3.1.1
Bus Parking
The PowerSpan II processor bus arbiter provides a flexible address bus parking scheme. When no
master is requesting the address bus, the processor bus arbiter can park on either the:
•
Last bus master
•
Specific bus master
The bus parking mode is determined by the PARK bit in the PB_ARB_CTRL Register. When specific
master mode is selected (PARK = 0), the BM_PARK[1:0] field selects the specific bus master for
address parking.
6.3.2
Data Bus Arbitration
The arbiter samples PB_TT[3] when PB_TS_ is asserted to generate data bus requests. The arbiter
grants the data bus to the current address bus owner by asserting one of PB_DBG[1:3]_ signals. The
signal is asserted, by default, one clock after PB_TS_. The PB arbiter can be programmed to sample
requests two clocks after the PB_TS_ signals is asserted. The arbiter is programmed through the
TS_DLY bit in the
“Processor Bus Arbiter Control Register” on page 307
.
Requesting masters are required to qualify bus grants before beginning an address tenure.
The parked master does not drive any address bus signals until it generates a request to use
the address bus.
An example application for this feature is some L2 caches hold the BR_ signal after the TS_
signal starts. The PowerSpan II arbiter could see this as a valid request and give the bus to the
L2 cache when the bus was not requested. This bit delays when the PB arbiter samples the
signal so a false bus request is not granted.
Содержание PowerSpan II
Страница 8: ...Contents 8 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 14: ...List of Tables 14 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 18: ...About this Document 18 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 82: ...2 PCI Interface 82 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 112: ...3 Processor Bus Interface 112 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 156: ...7 Interrupt Handling 156 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 380: ...12 Register Descriptions 380 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 394: ...14 Package Information 394 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 414: ...15 AC Timing 414 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 416: ...16 Ordering Information 416 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 420: ...A Hardware Implementation 420 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 428: ...B Typical Applications 428 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...
Страница 432: ...Glossary 432 PowerSpan II User Manual 80A1010_MA001_09 Integrated Device Technology www idt com ...