Specifications

AHB Monitor

The total number of different NRs and NWs states, that are valid, is dependent upon the

layer - some masters only perform reads and most have connections to only a subset of

the possible slaves. Similarly the number of valid Sb states is dependent upon the layer

because most masters are not capable of producing all possible burst types. For these

reasons, the format of the encoded signals has been developed to allow the bit allocation

per layer as stated in the previous section.

Assigning different states for Sequential and Nonsequential transfers means that it is

possible to reconstruct burst information from the data stream. It is not necessary to

identify either the transfer direction or the slave number in a sequential transfer because

the bus protocol defines that both of these must remain constant throughout a burst, so

is the same as the most recent NRs or NWs state. Similarly, it is not necessary to identify

the burst type in a nonsequential transfer because this is indicated in any subsequent

sequential transfers.

The Error_Next and Retry_Next responses are indicated during the first cycle of the two

cycle response sequence, which allows the progress of the burst in second cycle as can

occur with an error response.

Table 4-2 shows an example pattern of transfers and the data stream produced.

Table 4-2 Sample output

Pattern on bus Description

I Idle Transfer

WB First write transfer to slave 1 incurring one wait state imposed by the bus matrix

NW1 -

S_INCR4 Second write transfer to slave 1 in an incrementing burst of four

S_INCR4 Third write transfer to slave 1 in an incrementing burst of four

S_INCR4 Fourth write transfer to slave 1 in an incrementing burst of four

WB First read transfer from slave 2, one wait states from the bus connect latency and one

from the arbitration latency

WA -

NR2 -

WS Second read transfer from slave 2 in a wrapping burst of 4, one wait state inserted by

the slave

S_WRAP4 -