7 SCSI 7.1 GENERAL 7.2 SCSI AND INTERNAL DMA 7.3 SCSI CONTROLLER MODES Automatic Sequencer Mode 7 SCSI

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1 7 SCSI 7.1 GENERAL The ETRAX 100 has two SCSI ports, SCSI0 and SCSI1. The SCSI controller is compatible with SCSI-2 and SCSI-3 Fast-20. It is configurable as either two 8-bit wide SCSI interfaces or one 16-bit wide SCSI interface. It supports synchronous and asynchronous data transfer. Only initiator (host) mode can be used. The controller requires external bus drivers. 7.2 SCSI AND INTERNAL DMA During normal transfers the internal DMA channels are used for transferring data. SCSI port 0 uses the DMA channels 2 and 3, and SCSI port 1 uses the DMA channels 4 and 5. DMA descriptors in a linked list are used to transfer data and commands, see "DMA linked lists" on page SCSI CONTROLLER MODES The SCSI controller has three basic modes. One fully automatic, one fully manual (where each byte must be transferred by software) and one semi automatic mode. The most common command sequences can be run automatically, but processing is transferred to and continued in manual mode if the sequences in any way differ from what is expected. While in manual mode data can be transferred automatically with DMA, thus giving the semi automatic mode Automatic Sequencer Mode In the automatic mode a command is run without software intervention from start of arbitration to either a disconnect or the completion of the command. When a command is going to be executed a list of DMA descriptors are set up. The command is started by writing to a register and is processed entirely by hardware. The automatic mode can not handle all possible phase sequences involved in a SCSI command. Only the most common sequences are handled. These include: Normal command sequence Disconnect sequence Reselection sequence August 3, 2000 AXIS ETRAX 100 Data Sheet 67

2 If an automatic sequence runs into something unexpected, it will defer the rest of the processing to software and the processing must continue in manual mode. Examples of what must be handled in manual mode are parity errors and message rejects Manual Mode In manual mode each byte is transferred one at a time by reading or writing data to a register and then starting a single handshaking cycle by writing to the SCSI command register Semi Automatic Mode This mode is intended to speed up the data phases when running in manual mode. DMA is used to transfer all data automatically during a data in or data out phase. In this way it is possible to combine manual mode with full speed synchronous/asynchronous transfers. However, this is limited to the data phases. 7.4 EXTERNAL SCSI BUFFERS The ETRAX 100 SCSI interface requires external bus drivers. The SCSI signals can be divided in three groups, OR-tied, unidirectional, and bidirectional. The OR-tied signals must use open collector buffers. The other signals may use open collector buffers or active negation buffers, but if Fast-20 is used only active negation buffers are allowed for the non OR-tied signals. Signal type SCSI standard signals Buffers OR-tied, -RST, and Compatible to 74F38 open collector buffer Unidirectional -ATN, -ACK, -MSG, -C/D, -REQ, and -I/O Compatible to 74ABT244 Bidirectional -DB0, -DB1, -DB2, -DB3, -DB4, -DB5, -DB6, -DB7, and -DBP Compatible to 74ABT245 transceivers Table 7-1 Recommended buffers for SCSI external bus drivers Transceiver control When the SCSI interface is not using the bus, the active negation transceivers should be set in tristate mode. In ETRAX 100 this is done by setting to GND, and to VDD, as shown in the schematics and the timing diagrams included in this section. During arbitration the SCSI interface first drives and the data bus bit corresponding to its SCSI ID, and listens on the other data bus bits. This is accomplished by setting to GND, and to VDD. The SCSI ID can 68 AXIS ETRAX 100 Data Sheet August 3, 2000

3 either be selected by a strap or by software. In the latter case a Quick Switch, QS3251 (or compatible), has to be added. When the interface wins arbitration it drives. In ETRAX 100 this is done by setting to VDD. All other units on the bus then release the SCSI bus. The winner drives the -ATN signal, its own ID and the target ID bits on the data bus. This is accomplished by setting, and to VDD, and, and s0atn to GND. This gives the interface full control over its signals and all signals on the data bus have the same direction. s0atn, s0ack -ATN, -ACK s0msg, s0cd, s0io, s0req -MSG, -CD,, -REQ s0d<7:0>, s0p -DB<7:0>, -P -RST Figure bit SCSI external buffer with strapped ID August 3, 2000 AXIS ETRAX 100 Data Sheet 69

4 s0atn, s0ack -ATN, -ACK pb4 (3) s0msg, s0cd, s0io, s0req (1) -MSG, -CD,, -REQ (2) S<2:0> _ Y E QS3251 s0d<7:0>, s0p -DB<7:0>, -P -RST Note 1: s0req is input only. Note 2: s0msg, s0cd, and s0io are connected to the QuickSwitch (QS3251). Note 3: Use pb7 on s1-bus. Figure bit SCSI external buffer with software selectable ID s0atn, s0ack -ATN, -ACK s0msg, s0cd, s0io, s0req -MSG, -CD,, -REQ s1oe s1d<7:0>, s1p -DB<15:8>, -P1 s0d<7:0>, s0p -DB<7:0>, -P -RST Figure bit SCSI external buffer with strapped ID 70 AXIS ETRAX 100 Data Sheet August 3, 2000

5 s0atn, s0ack -ATN, -ACK pb4 s0msg, s0cd, s0io, s0req (1) s1oe (2) _ Y S<2:0> E QS3251 -MSG, -CD,, -REQ s1d<7:0>, s1p -DB<15:8>, -P1 s1bsy (2) S<2:0> _ Y E QS3251 s0d<7:0>, s0p -DB<7:0>, -P pb7 -RST Note 1: s0req is input only. Note 2: s0msg, s0cd, and s0io are connected to the QuickSwitches (QS3251) Figure bit SCSI external buffer with software selectable ID August 3, 2000 AXIS ETRAX 100 Data Sheet 71

6 7.4.2 External SCSI Buffer Timing ph, pb4, pb7 s0msg s0cd s0io pb4 SCSI-ID pb4 msg-out Iiden * -MSG -CD msg-out ARB Pre DB-Turn-Around SELECTION asserted by ETRAX asserted by Target s0atn -ATN Ioe * s0d -DB -DB I + T -ID -DB All-ID. OR-tied ETRAX-ID. OR-tied I + T -ID. Active Negation s0p -P * Iiden and Ioe are ETRAX 100 internal signals I + T -ID = Initiator + Target Identification Figure 7-5 SCSI timing 72 AXIS ETRAX 100 Data Sheet August 3, 2000

7 SCSI bus driven by target SCSI bus driven by ETRAX 100 SCSI bus released by ETRAX 100 t > 0 Ioe * s0d Target data Etrax 100 data Target data -DB Target data Etrax 100 data Target data * Ioe is an ETRAX 100 internal signal Figure 7-6 SCSI bus timing August 3, 2000 AXIS ETRAX 100 Data Sheet 73

8 74 AXIS ETRAX 100 Data Sheet August 3, 2000

SCSI is often the best choice of bus for high-specification systems. It has many advantages over IDE, these include:

13 SCSI 13.1 Introduction SCSI is often the best choice of bus for high-specification systems. It has many advantages over IDE, these include: A single bus system for up to seven connected devices. It