doc: Clarify ABI in SPARC CPU supplement

1 files changed, 16 insertions, 11 deletions

diff --git a/doc/cpu_supplement/sparc.t b/doc/cpu_supplement/sparc.t
index d0b7641e28..5ed0ec6334 100644
--- a/doc/cpu_supplement/sparc.t
+++ b/doc/cpu_supplement/sparc.t
@@ -214,11 +214,9 @@ initialization time.
 
 @section Calling Conventions
 
-
-Each high-level language compiler generates
-subroutine entry and exit code based upon a set of rules known
-as the compiler's calling convention.   These rules address the
-following issues:
+Each high-level language compiler generates subroutine entry and exit code
+based upon a set of rules known as the application binary interface (ABI)
+calling convention.   These rules address the following issues:
 
 @itemize @bullet
 @item register preservation and usage
@@ -228,12 +226,13 @@ following issues:
 @item call and return mechanism
 @end itemize
 
-A compiler's calling convention is of importance when
-interfacing to subroutines written in another language either
-assembly or high-level.  Even when the high-level language and
-target processor are the same, different compilers may use
-different calling conventions.  As a result, calling conventions
-are both processor and compiler dependent.
+An ABI calling convention is of importance when interfacing to subroutines
+written in another language either assembly or high-level.  It determines also
+the set of registers to be saved or restored during a context switch and
+interrupt processing.
+
+The ABI relevant for RTEMS on SPARC is defined by SYSTEM V APPLICATION BINARY
+INTERFACE, SPARC Processor Supplement, Third Edition.
 
 @subsection Programming Model
 
@@ -567,6 +566,12 @@ call and return mechanism does not automatically save and
 restore any registers.  This is accomplished via the save and
 restore instructions which manage the set of registers windows.
 
+In case a floating-point unit is supported, then floating-point return values
+appear in the floating-point registers.  Single-precision values occupy %f0;
+double-precision values occupy %f0 and %f1.  Otherwise, these are scratch
+registers.  Due to this the hardware and software floating-point ABIs are
+incompatible.
+
 @subsection Calling Mechanism
 
 All RTEMS directives are invoked using the regular