Bus Master Mode of PCI-Bus. Part III

Another method of setting the sequence of access to a bus is direct indication of a device that has got the highest priority which is carried out using the parameter “PCI Bus Parking” that enables to turn on/off the mode of device “parking” on PCI-bus. This parameter may have two values: Enabled and Disabled. If you set the value “Enabled”, a device on PCI-bus would have a full control over a bus for some time. This increases the operating productivity of this device but slows down the operation of the rest devices.

To control the data exchange via PCI-bus, use the parameter “Preempt PCI Master Option”. This parameter may have two values: Enabled and Disabled. If you set the value “Enabled”, the reading/writing operation on PCI-bus may be interrupted by some other system operations, for example, memory regeneration. The value “Disabled” enables the parallel operation that speeds up the system operation but may also cause some failures.

If you carry out reading/writing operations on PCI-bus the same way as on the other devices, you can use the buffering operation. It is necessary when the parameter “Preempt PCI Master Option” has got the value “Enabled”. During data reading, all recorded information are stored and transmitted as a packet at the end of reading, thus minimizing the required time. Use the parameter “ CPU Mstr Post-WR Buffer” to include the ability to use the buffer of posted record. But, unlike the other device, it is possible to identify several buffers for PCI-bus, that’s why this parameter may have the following values: NA – buffering is off; 1, 2, or 4 – a number of used buffers. The greater the number of buffer is used, the better.