[gcc r14-9094] pru: Document how -mmcu option uses MCU specs

[gcc r14-9094] pru: Document how -mmcu option uses MCU specs

[Dimitar Dimitrov]

https://gcc.gnu.org/g:608d40fde0c7e7e72a0acf4f262bf76c16443be0

commit r14-9094-g608d40fde0c7e7e72a0acf4f262bf76c16443be0
Author: Dimitar Dimitrov <dimitar@dinux.eu>
Date:   Thu Feb 1 19:19:54 2024 +0200

    pru: Document how -mmcu option uses MCU specs
    
    The plan to maintain PRU hardware-specific specs in newlib tree has been
    abandoned in favour of a new distinct GIT project.  Update the
    documentation accordingly.
    
    gcc/ChangeLog:
    
            * doc/invoke.texi (-mmcu): Add information about MCU specs.
    
    Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>

Diff:
---
 gcc/doc/invoke.texi | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 69020245b256..d75b28484bb2 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -30106,8 +30106,14 @@ This is already the norm for most firmware projects.
 
 @opindex mmcu
 @item -mmcu=@var{mcu}
-Specify the PRU MCU variant to use.  Check Newlib for the exact list of
-supported MCUs.
+Specify the PRU hardware variant to use.  A correspondingly named
+spec file would be loaded, passing the memory region sizes to
+the linker and defining hardware-specific C macros.
+
+Newlib provides only the @code{sim} spec, intended for running
+regression tests using a simulator.  Specs for real hardware can be
+obtained by installing the
+@w{@uref{https://github.com/dinuxbg/gnuprumcu/,GnuPruMcu}} package.
 
 @opindex mno-relax
 @item -mno-relax