MAC7200 datasheet(266/976 Pages) FREESCALE

266 / 976 page

Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

188

Freescale Semiconductor

NOTE

The actual RWA value as well as the CNT field within the RWCS are not

changed when executing a block read access. The original values can be

read by the external development tool at any time.

3. The data can then be read from the Read/Write Access Data Register (RWD) through the JTAG

access method outlined in Section 11.11.5.2, “Read/Write Access to Internal Nexus Registers,”

using the Nexus Register Index of 0xA (see Table 11-21).

4. Repeat Steps 3 and 4 in Section 11.11.5.3.3, “Single Read Access,” until the CNT value is zero (0).

When this occurs, the DV bit within the RWCS is set to indicate the end of the block read access.

11.11.5.4 Error Handling

The A7S Nexus3 module handles various error conditions as follows:

11.11.5.4.1

AHB Read/Write Error

All address and data errors that occur on read/write accesses to the AHB will return a transfer error

encoding on the HRESP[1:0] signals. If HRESP[1:0] = 2'b01:

1. The access is terminated without re-trying (AC bit is cleared)

2. The ERR bit in the RWCS Register is set

3. The Error Message is sent (TCODE = 8) indicating Read/Write Error

11.11.5.4.2

Access Termination

The following cases are defined for sequences of the Read/Write protocol that differ from those described

in the above sections.

1. If the AC bit in the RWCS Register is set to start Read/Write accesses and invalid values are loaded

into the RWD and/or RWA, then an AHB access error may occur. This is handled as described

above.

2. If a block access is in progress (all cycles not completed), and the RWCS Register is written, then

the original block access is terminated at the boundary of the nearest completed access.

a) If the RWCS is written with the AC bit set, the next Read/Write access will begin and the RWD

can be written to/ read from.

b) If the RWCS is written with the AC bit cleared, the Read/Write access is terminated at the

nearest completed access. This method can be used to break (early terminate) block accesses.

11.11.5.4.3

Read/Write Access Error Message

The Read/Write Access Error Message is sent out when an AHB access error (read or write) error has

occurred.

Error information is messaged out in the following format:

MAC7200 Datasheet(PDF) 266 Page - Freescale Semiconductor, Inc