QG80331M667 datasheet(45/67 Pages) INTEL

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Specification Update

Intel® 80331 I/O Processor

Core Errata

Accesses to the CP15 ID register with opcode2 > 0b001 returns

unpredictable values

Problem:

The ARM Architecture Reference Manual (ARM DDI 0100E) states the following in chapter B-2,

section 2.3:

When an <opcode2> value corresponding to an unimplemented or reserved ID register is

encountered, the System Control processor returns the value of the main ID register. ID registers

other than the main ID register are defined so that when implemented, their value cannot be equal

to that of the main ID register. Software can therefore determine whether they exist by reading both

the main ID register and the desired register and comparing their values. When the two values are

not equal, the desired register exists.

The Intel XScale® core does not implement any CP15 ID code registers other than the Main ID

unimplemented registers are accessed by software (e.g., mrc p15, 0, r3, c15, c15, 2), the value of

the Main ID register was to be returned. Instead, an unpredictable value is returned.

Workaround:

No workaround.

Status:

No Fix. See the Table , “Summary Table of Changes” on page 9.

Disabling and re-enabling the MMU can hang the core or cause it to execute

the wrong code

Problem:

When the MMU is disabled via the CP15 control register (CP15, CR1, opcode_2 = 0, bit 0) after

being enabled, certain timing cases can cause the processor to hang. In addition to this, re-enabling

the MMU after disabling it can cause the processor to fetch and execute code from the wrong

physical address. To avoid these issues, the code sequence below must be used whenever disabling

the MMU or re-enabling it afterwards.

Workaround:

The following code sequence can be used to disable and/or re-enable the MMU safely. The

alignment of the mcr instruction that disables or re-enables the MMU must be controlled carefully,

so that it resides in the first word of an instruction cache line.

@ The following code sequence takes r0 as a parameter. The value of r0 will be

@ written to the CP15 control register to either enable or disable the MMU.

mcr p15, 0, r0, c10, c4, 1 @ unlock I-TLB

mcr p15, 0, r0, c8, c5, 0 @ invalidate I-TLB

mrc p15, 0, r0, c2, c0, 0 @ CPWAIT

mov r0, r0

sub pc, pc, #4

b 1f @ branch to aligned code

.align 5

mcr p15, 0, r0, c1, c0, 0 @ enable/disable MMU, caches

mrc p15, 0, r0, c2, c0, 0 @ CPWAIT

mov r0, r0

sub pc, pc, #4

Status:

No Fix. See the Table , “Summary Table of Changes” on page 9.

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