
Glossary
SBO | See Should Be One. |
SBZ | See Should Be Zero. |
SBZP | See Should Be Zero or Preserved. |
Scan chain | A scan chain is made up of |
| technology using a standard JTAG TAP interface. Each device contains at least one TAP |
| controller containing shift registers that form the chain connected between TDI and |
| TDO, through which test data is shifted. Processors can contain several shift registers |
| to enable you to access selected parts of the device. |
Should Be One (SBO) |
|
| Should be written as 1 (or all 1s for bit fields) by software. Writing a 0 produces |
| Unpredictable results. |
Should Be Zero (SBZ) |
|
| Should be written as 0 (or all 0s for bit fields) by software. Writing a 1 produces |
| Unpredictable results. |
Should Be Zero or Preserved (SBZP)
Should be written as 0 (or all 0s for bit fields) by software, or preserved by writing the same value back that has been previously read from the same field on the same processor.
Unaligned | A data item stored at an address that is not divisible by the number of bytes that defines |
| the data size is said to be unaligned. For example, a word stored at an address that is not |
| divisible by four. |
Undefined | Indicates an instruction that generates an Undefined instruction trap. See the ARM |
| Architecture Reference Manual for more information on ARM exceptions. |
UNP | See Unpredictable. |
Unpredictable | Means that the behavior of the ETM cannot be relied on. Such conditions have not been |
| validated. When applied to the programming of an event resource, only the output of |
| that event resource is Unpredictable. |
| Unpredictable behavior can affect the behavior of the entire system, because the ETM |
| is capable of causing the core to enter debug state, and external outputs can be used for |
| other purposes. |
Unpredictable | For reads, the data returned when reading from this location is unpredictable. It can have |
| any value. For writes, writing to this location causes unpredictable behavior, or an |
| unpredictable change in device configuration. Unpredictable instructions must not halt |
| or hang the processor, or any part of the system. |
Copyright © 2006 ARM Limited. All rights reserved. | ARM DDI 0389B |