Specification Update

December 2008

12

5.

Problem:

If an exception occurs in thumb mode and a non-branch instruction is executed at the

corresponding exception vector, that instruction may execute twice. Instructions

located at exception vectors must be branch instructions that go to the appropriate

handler, but the ARM architecture allows the FIQ handler to be placed directly at the

FIQ vector (0x0000001c/0xffff001c) without requiring a branch. Because of this

condition, the first instruction of such an FIQ handler may be executed twice if it is not

a branch instruction.

non-branch instruction.

and there will not be any incorrect behavior. If a branch instruction is placed at the

beginning of the handler, it will not be executed twice.

Status:

No Fix.

6.

EX_IOWAIT_N Timing

Problem:

There are two problems with the functionality of the expansion bus IOWAIT protocol. If

both T2 and T3 are programmed to be 0 (normal timing), the expansion bus controller

will not extend the T3 data state as described in Section 12.4.1.5 “Using I/O Wait” on

- Rev. 001 (April 2007). This occurs because there is a synchronizer on the

EX_IOWAIT_N signal that causes the expansion bus controller to transition to the T4

state before the EX_IOWAIT_N is detected.

states that the expansion bus controller will transition to the T4 state upon the de-

assertion of EX_IOWAIT_N. The expansion bus controller does not do this — instead it

waits for the T3 count to expire before proceeding to T4.

2007).

and assurances made that EX_IOWAIT_N is asserted at least three cycles before the

deasserting edge of EX_RD_N. Additionally, the extended wait states will not be

changed after the deassertion of EX_IOWAIT_N.

Status:

No Fix.

7.

Ethernet Coprocessors — Ethernet Pad Enable Overrides Append FCS

Problem:

via the Ethernet Transmit Control Registers to either append or not append the FCS on

the transmitted Ethernet frames. When the frame payload size is less than 60 bytes,

the Pad Enable control bit has priority over the Append FCS control bit on whether or

not the FCS is appended on a frame.

Transmit frames even though the Append FCS control bit is not set because the Pad

Enable control bit overrides the Append FCS control bit.

Status:

No Fix.

8.

Ethernet Coprocessors — Length Errors on Received Frames

indicate length error on received frames only when stripping of pad bytes from the

received frame is enabled.

bit-1) is disabled will not be indicated to the NPE software when it reads the Receive

status. When pad stripping is enabled, length error indicates that the packet length is