Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus interface architecture
Reexamination Certificate
1999-06-30
2002-09-24
Auve, Glenn A. (Department: 2181)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus interface architecture
Reexamination Certificate
active
06457090
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to data transfers over a SCSI bus, and in particular to automated synchronous data transfers over a SCSI bus.
2. Description of Related Art
Prior single chip parallel SCSI host adapters have included a plurality of modules and an on-chip processor that controlled operation of the modules. For example, see U.S. Pat. No. 5,659,690, entitled “Programmably Configurable Host Adapter Integrated Circuit Including a RISC Processor,” issued on Aug. 19, 1997 to Stuber et al., which is incorporated herein by reference.
A typical parallel SCSI host adapter
100
included a SCSI module
130
(FIG.
1
), a sequencer
120
, data FIFO memory circuit
160
, a memory
140
, and a host interface module
110
that were interconnected by an internal chip I/O bus CIOBUS, which was used for control of host adapter integrated circuit
100
both by a host microprocessor
170
through a host adapter driver
165
and by sequencer
120
. The combination of host adapter driver
165
, sequencer
120
, and SCSI module
130
were used for controlling both synchronous and asynchronous transfers over SCSI bus
150
As is known to those of skill in the art, information transfers over SCSI bus
150
use a handshake method that utilizes request signals REQs and acknowledge signals ACKs. SCSI command, message, and status phases utilize only the asynchronous transfer mode in which an acknowledge signal ACK cannot be asserted until after a request signal REQ is asserted; request signal REQ cannot be de-asserted until acknowledge signal ACK is asserted; and acknowledge signal ACK cannot be de-asserted until signal REQ is re-asserted.
Synchronous data transfers are faster than asynchronous data transfers because the overhead is reduced. The SCSI data phase is the only phase that can transfer data using either a synchronous data transfer mode or an asynchronous data transfer mode. The synchronous data transfer mode is optional for the data phase, and must be negotiated between an initiator, e.g., host adapter
100
, and a target device, e.g., any one of SCSI peripherals
151
and
152
.
In the negotiation between initiator
100
and the target device, two parameters are determined, a transfer period and a REQ/ACK offset. The transfer period is the minimum time period from a rising edge of one request signal to the rising edge of the next request signal, and also is the minimum time period from a rising edge of one acknowledge signal to the rising edge of the next acknowledge signal. The width of the transfer period dictates the speed at which data can be transferred over SCSI bus
150
. The REQ/ACK offset is a maximum number of request signals REQs that a target device can send over SCSI bus
150
before an acknowledge signal ACK is received from host adapter.
Since the transfer period and REQ/ACK offset are dependent upon characteristics of the target device, they can be different for each target device
151
,
152
on SCSI bus
150
. While
FIG. 1
illustrates only two target devices, typically SCSI bus
150
can have up to sixteen target devices.
When host adapter
100
selects a target device, or is reselected by a target device, SCSI module
130
must be configured with the transfer period and the REQ/ACK offset for that target device. Typically, host adapter driver
165
provides the transfer period and the REQ/ACK offset in a sequencer control block (SCB) for the target device. Sequencer
120
transfers the transfer period and the REQ/ACK offset from the SCB for the selected or reselecting target device to a SCSI rate register and a SCSI offset register, respectively, in SCSI module
130
to configure SCSI module
130
for the data transfer.
This explanation of configuring SCSI module
130
assumed that host adapter driver had the REQ/ACK offset and the transfer period for the target device stored in a table in the host computer memory. However, initially the values of these parameters for a particular target device an unknown and must be determined by negotiation. The negotiation is done during the execution of a SCSI command specified in the SCB.
Host adapter driver
165
that manages host adapter
100
notifies sequencer
120
that a negotiation is required by loading an invalid transfer period in the SCB that is sent to host adapter
100
. During execution of the SCB, sequencer
120
detects the invalid transfer period. Those of skill in the art will appreciate that sequencer
120
is a processor that executes instructions. Thus, when it is stated that sequencer
120
takes a particular action this means that an instruction or sequence of instructions executed by sequencer
120
configures sequencer
120
so that the action is performed.
Upon detection of the invalid transfer period, sequencer
120
causes SCSI module
130
to assert the SCSI attention signal at the appropriate time during execution of the SCSI command according to the SCSI protocol, i.e., sequencer
120
programs the hardware so that the SCSI attention signal can be generated. The target device can respond to the SCSI attention signal either by entering a Message Out phase, or by ignoring the SCSI attention signal and entering a Command phase. If the SCSI attention signal is ignored, sequencer
120
continues with execution of the SCB by configuring SCSI module
130
for an asynchronous data transfer.
However, if the target device responds by entering the Message Out phase, sequencer
120
interrupts host adapter driver
165
with a request to execute the negotiation. Execution of the SCB by sequencer
120
is stopped for the negotiation because neither the transfer period nor the REQ/ACK offset is available to sequencer
120
.
In response to the interrupt, host adapter driver
165
conducts the negotiation to determine the values for the two parameters. When the negotiation is completed, host adapter driver
165
saves the values for the two parameters in a table within the host computer memory for future use. Host adapter driver
165
also loads the values in the SCB currently being executed by sequencer
120
, and into the appropriate registers in SCSI module
130
. Finally, host adapter driver
165
releases sequencer
120
so that execution of the SCB can continue. Hence, all the operations associated with configuring SCSI module
120
for a synchronous transfer are performed by sequencer
120
and host adapter driver
165
. The simple transfer of the transfer period and the REQ/ACK offset from the SCB to the appropriate registers required several sequencer instructions.
SUMMARY OF THE INVENTION
According to the principles of this invention, automating the setup of the data transfers enhances a data transfer during a SCSI data phase. Unlike the prior art host adapters that required a plurality of sequencer operations to configure the prior art SCSI module with the synchronous data transfer parameters, a SCSI module of this invention automatically configures the synchronous data transfer parameters using only hardware within the SCSI module of a parallel SCSI host adapter integrated circuit. The automatic configuration of the synchronous data transfer parameters eliminates the sequence of sequencer firmware instructions that were previously required to perform these operations as well as the time required to execute those firmware instructions.
In one embodiment, a parallel SCSI host adapter integrated circuit includes a memory containing a table having a plurality of entries. Each entry in the plurality of entries is a parameter used to configure the parallel SCSI host adapter integrated circuit for a data transfer over a SCSI bus to a target device. A target identification register stores a pointer to the table. A SCSI transfer parameter register is coupled to the memory. An entry in the plurality of entries pointed to by the value stored in the target identification register is loaded automatically into the SCSI transfer parameter register when a target identification (ID) is loaded into the target identification register.
Another SCSI transfer par
Adaptec, Inc.
Auve Glenn A.
Gunnison Forrest E.
Gunnison McKay & Hodgson, L.L.P.
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