Changeset 835ece1 in rtems-docs

Timestamp:

Nov 26, 2021, 1:42:03 PM (7 weeks ago)

Author:

Sebastian Huber <sebastian.huber@…>

Branches:

master

Children:

732d8bc

Parents:

87d1f4d

git-author:

Sebastian Huber <sebastian.huber@…> (11/26/21 13:42:03)

git-committer:

Sebastian Huber <sebastian.huber@…> (11/26/21 13:47:12)

Message:

cpu-supplement: Update trap handling for SPARC

Close #4459.

File:

• cpu-supplement/sparc.rst (modified) (4 diffs)

cpu-supplement/sparc.rst

@@ -1 +1 @@
 .. SPDX-License-Identifier: CC-BY-SA-4.0
 
+.. Copyright (C) 2021 embedded brains GmbH (http://www.embedded-brains.de)
 .. Copyright (C) 1988, 2002 On-Line Applications Research Corporation (OAR)
 
@@ -564 +565 @@
 and the following instruction.
 
+Trap Table
+----------
+
+A SPARC processor uses a trap table to execute the trap handler associated with
+a trap.  The trap table location is defined by the Trap Base Register
+(``TBR``).  The trap table has 256 entries.  Each entry has space for four
+instructions (16 bytes).  RTEMS uses a statically initialized trap table.  The
+start address of the trap table is associated with the ``trap_table`` global
+symbol.  The first action of the system initialization (entry points ``_start``
+and ``hard_reset``) is to set the ``TBR`` to ``trap_table``.  The interrupt
+traps (trap numbers 16 to 31) are connected with the RTEMS interrupt handling.
+Some traps are connected to standard services defined by the SPARC
+architecture, for example the window overflow, underflow, and flush handling.
+Most traps are connected to a fatal error handler.  The fatal error trap
+handler saves the processor context to an exception frame and starts the system
+termination procedure.
+
 Vectoring of Interrupt Handler
 ------------------------------
 
-Upon receipt of an interrupt the SPARC automatically performs the following
-actions:
-
-- disables traps (sets the ET bit of the ``PSR`` to 0),
-
-- the S bit of the ``PSR`` is copied into the Previous Supervisor Mode (PS) bit of
-  the ``PSR``,
+Upon receipt of an interrupt a SPARC processor automatically performs the
+following actions:
+
+- disables traps (sets the ``PSR.ET`` bit to 0 in the ``PSR``),
+
+- the ``PSR.S`` bit is copied into the Previous Supervisor Mode (``PSR.PS``)
+  bit in the ``PSR``,
 
 - the ``CWP`` is decremented by one (modulo the number of register windows) to
   activate a trap window,
 
-- the PC and nPC are loaded into local register 1 and 2 (l0 and l1),
-
-- the trap type (tt) field of the Trap Base Register (``TBR``) is set to the
-  appropriate value, and
+- the PC and nPC are loaded into local register 1 and 2 (``%l0`` and ``%l1``),
+
+- the trap type (``tt``) field of the Trap Base Register (``TBR``) is set to
+  the appropriate value, and
 
 - if the trap is not a reset, then the PC is written with the contents of the
-  ``TBR`` and the nPC is written with ``TBR`` + 4.  If the trap is a reset, then the PC
-  is set to zero and the nPC is set to 4.
+  ``TBR`` and the nPC is written with ``TBR`` + 4.  If the trap is a reset,
+  then the PC is set to zero and the nPC is set to 4.
 
 Trap processing on the SPARC has two features which are noticeably different
@@ -591 +609 @@
 register in effect immediately before the trap occurred is not explicitly
 saved.  Instead only reversible alterations are made to it.  Second, the
-Processor Interrupt Level (pil) is not set to correspond to that of the
-interrupt being processed.  When a trap occurs, ALL subsequent traps are
+Processor Interrupt Level (``PSR.PIL``) is not set to correspond to that of the
+interrupt being processed.  When a trap occurs, **all** subsequent traps are
 disabled.  In order to safely invoke a subroutine during trap handling, traps
 must be enabled to allow for the possibility of register window overflow and
@@ -699 +717 @@
 by default, trap handlers would execute on the stack of the RTEMS task which
 they interrupted.  This artificially inflates the stack requirements for each
-task since EVERY task stack would have to include enough space to account for
-the worst case interrupt stack requirements in addition to it's own worst case
-usage.  RTEMS addresses this problem on the SPARC by providing a dedicated
+task since **every** task stack would have to include enough space to account
+for the worst case interrupt stack requirements in addition to it's own worst
+case usage.  RTEMS addresses this problem on the SPARC by providing a dedicated
 interrupt stack managed by software.
 
-During system initialization, RTEMS allocates the interrupt stack from the
-Workspace Area.  The amount of memory allocated for the interrupt stack is
-determined by the interrupt_stack_size field in the CPU Configuration Table.
-As part of processing a non-nested interrupt, RTEMS will switch to the
+The interrupt stack is statically allocated by RTEMS.  There is one interrupt
+stack for each configured processor.  The interrupt stack is used to initialize
+the system.  The amount of memory allocated for the interrupt stack is
+determined by the ``CONFIGURE_INTERRUPT_STACK_SIZE`` application configuration
+option.  As part of processing a non-nested interrupt, RTEMS will switch to the
 interrupt stack before invoking the installed handler.