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How do I tell whether I am on a Morello machine?
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Every Arm processor has a *main id register* ``MDIR_EL1`` which
contains a unique CPUID identity number for the system.
The full 32-bit CPUID value for Morello is ``0x3F0F4120``, as specified
in the `Morello Technical Reference Manual <https://developer.arm.com/documentation/102278/latest>`_.

You can query the main id register using the C code below, with the
inline assembler to fetch the ``MDIR_EL1`` value.

.. code-block:: C
   :emphasize-lines: 12

   #include <stdio.h>

   /* see Arm Morello System Development Platform
    * Technical Reference Manual
    * Document ID: 102278_0001_04_en Issue: 04 Rainier clusters
    * Appendix B2 Main ID Register, MIDR_EL1
    */
   #define MORELLO 0x3f0f4120
   
   int main() {
     long arm_cpuid;
     __asm__("mrs %0, MIDR_EL1" : "=r"(arm_cpuid));
     printf("CPU ID %lx\n", arm_cpuid);
     if (arm_cpuid == MORELLO)
       printf("This is a Morello prototype system\n");
     return 0;
   }