updated Morello build instructions, based on my experience

building on CheriBSD 22.12

Author: jeremysinger

ports/unix/README-morello.md

@@ -1,23 +1,41 @@
-# Compiling on Morello
+# Compiling MicroPython on Morello
 
-I compiled MicroPython directly on the CheriBSD/Morello machine, using the
-`llvm-morello` toolchain and `gmake`. The makefiles are not compatible with
-BSD `make`.
+MicroPython can be compiled using hybrid tools on a CheriBSD/Morello machine.
+It's possible to compile both hybrid and purecap builds for MicroPython.
+
+## Dependencies
+
+On CheriBSD 22.12, the following packages need to be installed:
+
+```
+pkg64 install git gmake libffi llvm-morello pkgconf python3
+```
+
+For building purecap MicroPython, the purecap libffi is also required:
+
+```
+pkg64c install libffi
+```
+
+Note the requirement to use `gmake` rather than the default BSD `make`.
+Also note that MicroPython build requires a working Python interpreter.
 
 ## Hybrid ABI
 
-To compile MicroPython for the Hybrid ABI, execute the following command in this folder:
+To compile MicroPython for the Hybrid ABI, execute the following commands in this folder:
 
 ```
+gmake CC='clang-morello' CXX='clang++-morello' submodules
 gmake CC='clang-morello' CXX='clang++-morello'
 ```
 
 ## Purecap ABI
 
-To compile MicroPython for the Purecap ABI, execute the following command in this folder:
+To compile MicroPython for the purecap ABI, execute the following commands in this folder:
 
 ```
-gmake CC='clang-morello -march=morello+c64 -mabi=purecap' CXX='clang++-morello -march=morello+c64 -mabi=purecap' LIBFFI_LDFLAGS='-L/usr/local/lib -lffi'
+gmake CC='clang-morello -march=morello -mabi=purecap' CXX='clang++-morello -march=morello -mabi=purecap' LIBFFI_LDFLAGS='-L/usr/local/lib -lffi' submodules
+gmake CC='clang-morello -march=morello -mabi=purecap' CXX='clang++-morello -march=morello -mabi=purecap' LIBFFI_LDFLAGS='-L/usr/local/lib -lffi'
 ```
 
 The `LIBFFI_LDFLAGS` argument can be omitted if FFI has been turned off in `mpconfigport.mk` 
@@ -27,4 +45,3 @@ The `LIBFFI_LDFLAGS` argument can be omitted if FFI has been turned off in `mpco
 To compile the coverage variant, simply append `VARIANT=coverage` to the `gmake` command.
 If you get an internal error in Clang, remove the two lines in
 `variants/coverage/mpconfigvariant.h` which add the flags`-fprofile-arcs -ftest-coverage`.
-