ICC_MSRE, Interrupt Controller Monitor System Register Enable register
The ICC_MSRE characteristics are:
Purpose
Controls whether the System register interface or the memory-mapped interface to the GIC CPU interface is used for EL3.
Configuration
AArch32 System register ICC_MSRE bits [31:0] can be mapped to AArch64 System register ICC_SRE_EL3[31:0] , but this is not architecturally mandated.
Some or all RW fields of this register have defined reset values. These apply only if the PE resets into an Exception level that is using AArch32. Otherwise, RW fields in this register reset to architecturally UNKNOWN values.
Attributes
ICC_MSRE is a 32-bit register.
Field descriptions
The ICC_MSRE bit assignments are:
Bits [31:4]
Reserved, RES0.
Enable, bit [3]
Enable. Enables lower Exception level access to ICC_SRE and ICC_HSRE.
| Enable | Meaning |
|---|---|
| 0b0 |
Secure EL1 accesses to Secure ICC_SRE trap to EL3. EL2 accesses to Non-secure ICC_SRE and ICC_HSRE trap to EL3. Non-secure EL1 accesses to ICC_SRE trap to EL3, unless these accesses are trapped to EL2 as a result of ICC_HSRE.Enable == 0. |
| 0b1 |
Secure EL1 accesses to Secure ICC_SRE do not trap to EL3. EL2 accesses to Non-secure ICC_SRE and ICC_HSRE do not trap to EL3. Non-secure EL1 accesses to ICC_SRE do not trap to EL3. |
If ICC_MSRE.SRE is RAO/WI, an implementation is permitted to make the Enable bit RAO/WI.
If ICC_MSRE.SRE is 0, the Enable bit behaves as 1 for all purposes other than reading the value of the bit.
This field resets to an architecturally UNKNOWN value.
DIB, bit [2]
Disable IRQ bypass.
| DIB | Meaning |
|---|---|
| 0b0 |
IRQ bypass enabled. |
| 0b1 |
IRQ bypass disabled. |
In systems that do not support IRQ bypass, this bit is RAO/WI.
This field resets to 0.
DFB, bit [1]
Disable FIQ bypass.
| DFB | Meaning |
|---|---|
| 0b0 |
FIQ bypass enabled. |
| 0b1 |
FIQ bypass disabled. |
In systems that do not support FIQ bypass, this bit is RAO/WI.
This field resets to 0.
SRE, bit [0]
System Register Enable.
| SRE | Meaning |
|---|---|
| 0b0 |
The memory-mapped interface must be used. Accesses at EL3 or below to any ICH_* System register, or any EL1, EL2, or EL3 ICC_* register other than ICC_SRE, ICC_HSRE, or ICC_MSRE, are UNDEFINED. |
| 0b1 |
The System register interface to the ICH_* registers and the EL1, EL2, and EL3 ICC_* registers is enabled for EL3. |
If software changes this bit from 1 to 0, the results are UNPREDICTABLE.
If an implementation supports only a System register interface to the GIC CPU interface, this bit is RAO/WI.
This field resets to 0.
Accessing the ICC_MSRE
This register is always System register accessible.
The GIC architecture permits, but does not require, that registers can be shared between memory-mapped registers and the equivalent System registers. This means that if the memory-mapped registers have been accessed while ICC_MSRE.SRE==0, then the System registers might be modified. Therefore, software must only rely on the reset values of the System registers if there has been no use of the GIC functionality while the memory-mapped registers are in use. Otherwise, the System register values must be treated as UNKNOWN.
This register is only accessible when executing in Monitor mode.
Accesses to this register use the following encodings:
MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}
| coproc | opc1 | CRn | CRm | opc2 |
|---|---|---|---|---|
| 0b1111 | 0b110 | 0b1100 | 0b1100 | 0b101 |
if PSTATE.EL == EL0 then
UNDEFINED;
elsif PSTATE.EL == EL1 then
if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T12 == '1' then
AArch64.AArch32SystemAccessTrap(EL2, 0x03);
elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T12 == '1' then
AArch32.TakeHypTrapException(0x03);
else
UNDEFINED;
elsif PSTATE.EL == EL2 then
UNDEFINED;
elsif PSTATE.EL == EL3 then
return ICC_MSRE;
MCR{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}
| coproc | opc1 | CRn | CRm | opc2 |
|---|---|---|---|---|
| 0b1111 | 0b110 | 0b1100 | 0b1100 | 0b101 |
if PSTATE.EL == EL0 then
UNDEFINED;
elsif PSTATE.EL == EL1 then
if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T12 == '1' then
AArch64.AArch32SystemAccessTrap(EL2, 0x03);
elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T12 == '1' then
AArch32.TakeHypTrapException(0x03);
else
UNDEFINED;
elsif PSTATE.EL == EL2 then
UNDEFINED;
elsif PSTATE.EL == EL3 then
if SCR.NS == '0' && CP15SDISABLE2 == HIGH then
UNDEFINED;
else
ICC_MSRE = R[t];