gem5: minimally test VExpress_GEM5_V2

README.adoc

@@ -1328,6 +1328,8 @@ The reason for that is that on baremetal we don't parse the <<device-tree,device
 ./run --arch aarch64 --baremetal userland/c/hello.c --emulator gem5 --machine RealViewPBX
 ....
 
+see also: xref:gem5-arm-platforms[xrefstyle=full].
+
 This generates yet new separate images with new magic constants:
 
 ....
@@ -12187,6 +12189,19 @@ xdg-open "$(./getvar --arch aarch64 --gem5-build-id ruby gem5_build_build_dir)/A
 
 A minimized ruby config which was not merged upstream can be found for study at: https://gem5-review.googlesource.com/c/public/gem5/+/13599/1
 
+=== gem5 ARM platforms
+
+The gem5 platform is selectable with the `--machine` option, which is named after the analogous QEMU `-machine` option, and which sets the `--machine-type`.
+
+Each platform represents a different system with different devices, memory and interrupt setup.
+
+TODO: describe the main characteristics of each platform, as of gem5 5e83d703522a71ec4f3eb61a01acd8c53f6f3860:
+
+* `VExpress_GEM5_V1`: good sane base platform
+* `VExpress_GEM5_V1_DPU`: `VExpress_GEM5_V1` with DP650 instead of HDLCD, selected automatically by `./run --dp650`, see also: <<gem5-graphic-mode-dp650>>
+* `VExpress_GEM5_V2`: VExpress_GEM5_V1 with GICv3, uses a different bootloader `arm/aarch64_bootloader/boot_emm_v2.arm64` TODO is it because of GICv3?
+* anything that does not start with: `VExpress_GEM5_`: old and bad, don't use them
+
 === gem5 internals
 
 ==== gem5 Python C++ interaction