Atmel AT697E [ERRATA SHEET]

4409D-AERO-04/12

2

Errata Description

1.

Multiplier/Divider Failure on Negative Operands Treatments

The embedded multiplier/divider block can generate wrong values when negative operands are used. The bug occurs

with negative dividends and positive divisors. As the dividend is 64-bit including the y register, the y-register needs to be

initialised to a negative value in order to reproduce this error.

In all cases observed, the absolute error is a maximum of 2, but in case of small quotients, this can be a large relative

error, for example -2/1 = 0 instead of -2. Since the bug can also cause zero or sign change, the ICC flags can also be

wrong.

This Multiplier/Divider failure is due to a LEON2 VHDL model error.

Workarounds

If you want to maintain the hardware multiplier functional, it is sufficient to avoid negative operands or to avoid SDIV

operations.

If you do not need the multiplier to remain available, you can simply not use the -mv8 flag when compiling the project

with LECCS / BCC / RCC compilers. This will disable use of both the divider and the multiplier.

2.

Call Return Address Failure with Large Displacement

CALL instruction saves the return address in an FPU register rather than in an IU %o7 register when the call address is

larger than 64Mbytes (forward) or 8Mbytes(backward). The return address is normally expected by the return operation

in %o7 register at the end of a called function.

The bug is triggered exactly and only by opcodes matching the following condition:(bit 31 == 0) & (bit 30 == 1) & (bit 24

== 1) & (bit 21 == 0)

corresponding to bits 26/23 of the offset in terms of byte addresses.

As a consequence, the failure will only occur if the displacement is >= 64 MByte for forward calls or >= 8 MByte for

backward calls. Due to the specific condition however, not all calls above this limit will trigger the failure.

The called function is executed normally, but the return fails.

This “Call Return Address” failure is due to a LEON2 VHDL model error.

Workarounds

Use only calls with an address displacement smaller than 64 Mbytes (forward) or 8 Mbytes (backward).

If dynamic linking is used, the memory configuration should be constrained to avoid calls beyond the given limits. If the

operating system is moved to the upper memory area, all OS calls are forward calls, allowing the use of up to 64 MByte

program memory.

3.

Byte and Half-word Write to SRAM Failure when Executing from SDRAM

If an application is executing in SDRAM, byte- and half-word writes to SRAM can fail if the EDAC or read-modify-write

cycles are used.

This “SRAM Write access” failure is due to a LEON2 VHDL model error.

Workarounds

Do not perform byte and half-word write operations to SRAM when executing code from SDRAM (in assembler

language, byte/half-word stores are performed by the instructions STB, STH, LDSTUB -- CLRB and CLRH also, they

are

synthetic instructions for STB and STH -- and their alternate space equivalents, whereas in C-code, they are typically

assignments to char and short data types).