IBM Translation Control Entry

A Translation Control Entry (TCE) on IBM eServer pSeries computers is used by the I/O bridge to translate addresses generated by I/O devices into physical addresses. The technology is also called an I/O memory management unit, or IOMMU.

External links

• ibm.com "Logical Partition Security in the IBM eServer pSeries 690", an explanation of logical partitioning on IBM pSeries systems.

Generally speaking, a Peripheral Component Interconnect (PCI) host bridge provides communications between a processor and an input/output (I/O) subsystem within a data processing system. The PCI host bridge provides data buffering capabilities to allow read and write data to be transferred between the processor and the I/O subsystem. The I/O subsystem can be a group of PCI devices connected to a PCI bus. When a PCI device on the PCI bus originates a read or write command to a system memory via a direct memory access (DMA), the PCI host bridge translates a PCI address of the DMA to a system memory address of the system memory.

Each PCI device on the PCI bus is associated with a corresponding translation control entry (TCE) table resided within the system memory. The TCE tables can be utilized to preform TCE translations from PCI addresses to system memory addresses. In response to a DMA read or write operation, a corresponding TCE table is read by the PCI host bridge to provide a TCE translation.