baremetal: arm multicore attempt

README.adoc

@@ -10419,7 +10419,13 @@ help architecture
 
 shows ARM version up to `armv6`, so maybe `armv6` is not implemented?
 
-=== ARM exception level
+=== ARM baremetal
+
+In this section we will focus on learning ARM architecture concepts that can only learnt on baremetal setups.
+
+Userland information can be found at: https://github.com/cirosantilli/arm-assembly-cheat
+
+==== ARM exception level
 
 ARM exception levels are analogous to x86 <<ring0,rings>>.
 
@@ -10491,6 +10497,25 @@ output:
 3
 ....
 
+==== ARM multicore
+
+TODO get working: CPU1 not waking up:
+
+....
+./run --arch aarch64 --baremetal arch/aarch64/no_bootloader/multicore
+....
+
+Source: link:baremetal/arch/aarch64/no_bootloader/multicore.S[]
+
+CPU 0 of this program enters a spinlock loop: it repeatedly checks if a given memory address is `1`.
+
+So, we need CPU 1 to come to the rescue to that memory address be `1`, otherwise CPU 0 will be stuck there forever.
+
+Bibliography:
+
+* https://stackoverflow.com/questions/20055754/arm-start-wakeup-bringup-the-other-cpu-cores-aps-and-pass-execution-start-addre
+* https://stackoverflow.com/questions/980999/what-does-multicore-assembly-language-look-like/33651438#33651438
+
 === How we got some baremetal stuff to work
 
 It is nice when thing just work.