Revisions: IC660ELB912A , IC660ELB912B , IC660ELB912C , IC660ELB912D , IC660ELB912E , IC660ELB912F , IC660ELB912G , IC660ELB912H , IC660ELB912I , IC660ELB912J , IC660ELB912K , IC660ELB912L , IC660ELB912M , IC660ELB912N , IC660ELB912O , IC660ELB912P , IC660ELB912Q , IC660ELB912R , IC660ELB912S , IC660ELB912T , IC660ELB912U , IC660ELB912V , IC660ELB912W , IC660ELB912X , IC660ELB912Y , IC660ELB912Z ,
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SHARED RAM INTERFACE As you remember, all data passed between the Host system and the. PCIM goes through Host shared RAM, referred to as the Shared RAM Interface (SRI). As stated, this RAM looks like an 16Kx8 static memory device to the Host system. Although all areas of RAM are read/write , that is, fully accessible by the Host to read or write to any RAM location, some areas of the RAM are not accessed by the Software Driver during normal operation (as shown in figure 2.4). Shared RAM Updates Some data is transferred between the Shared RAM and the serial bus automatically by the PCIM manager. This type of communication includes I/O circuit updates, fault reports, and the like. The rest of the calls and message types must be initiated by the Host system using the Software Driver, explained in more detail in chapter 4. Device tog In The PCIM Manager will log in a device whenever control data is received from a device that is NOT listed in the Host s SRI. A device is considered logged in, or on-line, when the PCIM Manager has that device s configuration data translated and stored in the SRI (a GetBusConfig call can be used to verify the presence of the device on the bus). At this point, the device is considered logged in and input control data from that device will be transferred to the SRI Input Table. Heavy log in activity occurs after power up of the PCIM Manager if there are no devices logged in the SRI. Once in steady state, Jog in activity occurs whenever Broadcast Control data is received from a device that has just been included on the serial bus. You may want to code the InitlM call (see chapter 4) in your program logic first (in order to allow devices on the bus to log in with the PCIM), and then perform the rest of your program logic initializations in order to optimize front-end timing. Device Log Out The PClM Manager will log a device out whenever Broadcast Control data is not received for three (3) consecutive serial bus scans. This timeout period is fixed by the PCIM Manager. When Device Log Out occurs, the PCIM Manager will not direct output data to that device from the Serial Interface, and will inform the Host of the Loss of Device. The device remains logged off until the PCIM Manager receives identification data from it. When new Broadcast Control data is received from any device which is not logged in, the PCIM Manager will begin its device log in procedure. Memory Configuration Following is the memory map for the PCIM 16K Shared RAM Interface. It shows the different areas used to convey data, status, control and diagnostic information to and from the Host system. A complete map of the Shared RAM Interface is shown in figure * Host write to these locations causes Interrupt to PCIM Manager Figure 2.4 Shared RAM Interface Map (Cont d). Theory of Operation 2-l 7 GFK-0074 I/O Table Lockout To ensure data coherency for all control data to and from the Host, the PCN Manager will implement a lockout of all control data tables during an I/O Lockout Request. This feature prevents the PClM Manager from accessing the SRI at the same time that the Host is updating it. Two bytes in the Shared RAM Interface (SRI) are dedicated to the I/O Lockout feature: I/O lockout Request/Relinquish, and t/O Table Lockout State. The maximum response time to the t/O Table Lockout Request will be determined by the time required for the PCIM Manager to transfer 128 bytes to or from the Input or Output Table. Normally, the response will be less than this time. However, if the PCIM Manager is currently transferring data to or from the Input or Output Table, it will complete the current data transfer before accepting and enabling the lockout. When the Host has completed its control data access, the PCIM Manager will resume normal operation in servicing control data to and from the SRI. Device I/O Table The Device l/O Table resides in the last 8K bytes of the Shared RAM memory and is divided into two tables - the Device Input Table, and the Device Output Table (see chapter 5). The Input Table wili contain the Broadcast Control Data from each logged in device. The input Table is updated every serial bus scan unless I/O Lockout is enabled. Data placed in the Output Table by the Host will be sent to each logged in device every serial bus scan. Both the Input and Output Tables are organized in groups of up to 32 segments each (corresponding to the maximum possible number of devices on the bus). Segment lengths are fixed at 128 bytes. Jnput Table All Broadcast Controt Data will be placed in the Input Table in the segment associated with that particular device. That is, control data from device #I2 will be placed in segment 12. As such, the Input Table can be thought of as an array table. The Host will be able to determine the type of I/O Block from the Device Configuration Table. Output Table The PClM Manager will take the data placed in the Output Table and direct that data to the device associated with the given Output Table segment. If the Host wants to send control data to I/O Block #l2, it must place that data in segment 12 of the Output Table. As with the Input Table, the format of each individual segment is established in the lnitlM call. 2-1 8 Theory of Operation PCIM Broadcast Control Output Table The PCIM Manager will transmit its own Broadcast Control Data onto the serial bus once per scan. The Host will place data in the Broadcast Control Output Table for the PCIM Manager to broadcast (see chapter 5). PCIM Directed Control Input Table The PCIM Manager may receive Directed Control Data from any device capable of sending this type of message to the PCIM. The Directed Control Input Table is provided in the SRI for this data (see chapter 5). Thus, a series of Hosts may be placed on a single bus and communicate with each other. Using the Broadcast Control Output Table, all PCIMs can broadcast control data to all other PClMs on that serial bus. Using the Directed Control input Table, a single PCIM can be controlled by another PCIM. This a powerful feature of the PCIM Manager. Device Configuration Table The Device Configuration Table, 256 bytes long, contains the device ID, status, setup and other characteristics of each device connected to the serial bus controlled by this PCIM. Parameters are received by the PCIM Manager via an InitlM or ChglMSetup call. These tables are formatted into 32 segments of 8 bytes per segment. One 8 byte segment is reserved for each of the 32 possible devices, with the lowest, device number 0, residing in the first 8 byte segment. PCIM Setup Table The PCIM Setup Table contains parameters unique to a particular PCIM. These parameters consist of device related values. When the Host changes one or more of these parameters, the PCIM Manager will log all devices out of the database and drop all bus transmissions for 1.5 seconds, the time period necessary to cause all receiving devices to log out the PCIM. When the PCIM begins re-transmitting, these devices will re-log in to the PCIM with the new parameters. PCIM Status Table The PCIM Status Table contains six bytes indicating the veracity of the PCIM software and the status of the PCIM hardware. When certain status bits change, the PCIM Manager will set the PCIM Status Change byte in the Interrupt Status Table. If this interrupt is not disabled, the PCIM Manager also will cause a Host interrupt to occur. interrupt Status will be set when for a RAM fault, an EPROM fault, or for excessive bus errors. Theory of Operation 2-19 GFK-0074 Interrupt Tables Several conditions occur which can cause the PCIM Manager to set a byte in the Interrupt Status Table, and possibly result in the generation of an interrupt for the Host. The following is an explanation of each condition: - Interrupt Summary Status - Whenever the PClM Manager causes an interrupt to the Host, the interrupt Summary Status byte will be set in the Interrupt Status Table. If this byte is set in the Interrupt Disable Table, the PCIM Manager will not interrupt the Host for any reason. ? Request Queue Entry - Certain messages received from devices on the bus will be separated out from all other messages and placed in the Request Queue. The PCIM Manager will then set the Request Queue Entry byte. - PCIM Status Change - When certain items within the PCIM Status Table change, the PCIM Manager will indicate this change by setting the PClM Status Change byte. - Device Status Change - Anytime that a device on the bus is logged in, logged out or changes its configuration data, the PCIM Manager will set the Device Status Change byte. - Outputs Sent - This status byte is set whenever the PCIM relinquishes its access to the serial bus. This interrupt status can be used to synchronize to the serial bus scan if required. - Command Complete - Each time the Host initiates a command, and the PCIM Manager completes that command (with or without errors), this status byte will be set. - Receive Queue Not Empty - Whenever any message is received from a device on the serial bus that is not part of Request Queue Entry, Serial Bus Requests, or a response from the command Transmit with Reply, this status byte will be set. Since these messages will be queued, the Host may retrieve them via the Read Datagram Command. - I/O Table Lockout Grant - When the Host requests an l/O Table Lockout (not a Relinquish), this byte will be set to indicate when the PClM Manager is able to enforce the lockout. The lockout is not enforced until this byte is returned to the Host. |
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