• State Accepted Answer
  • Locked Locked
  • Replies 6 replies
  • Subscribers 346 subscribers
  • Views 8199 views
  • Users 0 members are here
Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

AMBA AHB

VT

Hi ,

In AHB specs, There is one note as below.

Note

Every slave must have a predetermined maximum number of wait states that it will insert before it backs off the bus, in order to allow the calculation of the latency of accessing the bus. It is recommended, but not mandatory, that slaves do not insert more than 16 wait states to prevent any single access locking the bus for a large number of clock cycles.

we have to care for this while design or in verification, if this scenario has to be checked then ??? If yes then after 16 wait state , slave must be give HREADY high after 16 wait state. Right?

Kindly do needful.

Thanks in advance.

Parents
  • 0

    Hi Ajoo,

    The maximum 16 cycles before possibly giving a RETRY or SPLIT response (during which HREADY will be driven high) is only a protocol recommendation, 16 cycles seen as possibly a reasonable maximum time you might be able to accept your bus stalled to other master accesses.

    If you only had one master on your bus you could simply ignore this recommendation (unless you wanted to consider if the slave was sensibly designed - does it really need that many wait states to respond ? - is the slave still functioning ?)

    Or if it was imperative that this slave access completed before anything else could sensibly happen in your system, regardless of how many wait states that was, you as the system designer would decide whether this 16 cycle recommendation was appropriate.

    If you are using some sort of protocol checker, it might report if the 16 cycle "maximum" is exceeded, but this should only be reported as an advisory "warning", not a "protocol violation".

    So the 16 cycle recommendation is an advisory point, at which time you need to consider if the slave is sensibly designed, and if you need to consider responding with a SPLIT or RETRY response to allow other masters to access the bus.

    Remember it is a design "recommendation", not a protocol "requirement", so use the figure of 16 as appropriate for your application.

    JD

Reply
  • 0

    Hi Ajoo,

    The maximum 16 cycles before possibly giving a RETRY or SPLIT response (during which HREADY will be driven high) is only a protocol recommendation, 16 cycles seen as possibly a reasonable maximum time you might be able to accept your bus stalled to other master accesses.

    If you only had one master on your bus you could simply ignore this recommendation (unless you wanted to consider if the slave was sensibly designed - does it really need that many wait states to respond ? - is the slave still functioning ?)

    Or if it was imperative that this slave access completed before anything else could sensibly happen in your system, regardless of how many wait states that was, you as the system designer would decide whether this 16 cycle recommendation was appropriate.

    If you are using some sort of protocol checker, it might report if the 16 cycle "maximum" is exceeded, but this should only be reported as an advisory "warning", not a "protocol violation".

    So the 16 cycle recommendation is an advisory point, at which time you need to consider if the slave is sensibly designed, and if you need to consider responding with a SPLIT or RETRY response to allow other masters to access the bus.

    Remember it is a design "recommendation", not a protocol "requirement", so use the figure of 16 as appropriate for your application.

    JD

Children