cpukit/microblaze: Add debug vector and handler

This patch adds a vector for debug events along with a hook similar to
the exception framework. The debug vector generates an exception frame
for use by libdebugger.

bsps/microblaze/microblaze_fpga/start/_debug_sw_break_handler.S

@@ -0,0 +1,106 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+
+/**
+ * @file
+ *
+ * @ingroup RTEMSBSPsMicroBlaze
+ *
+ * @brief MicroBlaze debug trap handler implementation
+ */
+
+/*
+ * Copyright (C) 2022 On-Line Applications Research Corporation (OAR)
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <rtems/score/cpu.h>
+
+	.text
+	.globl _debug_sw_break_handler    # HW Exception Handler Label
+	.extern _MicroBlaze_Debug_handle
+	.align 2
+
+	_debug_sw_break_handler:
+	/* The stack used here does not matter since debug cannot recurse */
+
+	/* Subtract exception frame */
+	addik r1, r1, -(CPU_EXCEPTION_FRAME_SIZE)
+
+	/* Store program state */
+	swi  r2, r1, MICROBLAZE_EXCEPTION_FRAME_R2
+	swi  r3, r1, MICROBLAZE_EXCEPTION_FRAME_R3
+	swi  r4, r1, MICROBLAZE_EXCEPTION_FRAME_R4
+	swi  r5, r1, MICROBLAZE_EXCEPTION_FRAME_R5
+	swi  r6, r1, MICROBLAZE_EXCEPTION_FRAME_R6
+	swi  r7, r1, MICROBLAZE_EXCEPTION_FRAME_R7
+	swi  r8, r1, MICROBLAZE_EXCEPTION_FRAME_R8
+	swi  r9, r1, MICROBLAZE_EXCEPTION_FRAME_R9
+	swi r10, r1, MICROBLAZE_EXCEPTION_FRAME_R10
+	swi r11, r1, MICROBLAZE_EXCEPTION_FRAME_R11
+	swi r12, r1, MICROBLAZE_EXCEPTION_FRAME_R12
+	swi r13, r1, MICROBLAZE_EXCEPTION_FRAME_R13
+	swi r14, r1, MICROBLAZE_EXCEPTION_FRAME_R14
+	swi r15, r1, MICROBLAZE_EXCEPTION_FRAME_R15
+	swi r16, r1, MICROBLAZE_EXCEPTION_FRAME_R16
+	swi r17, r1, MICROBLAZE_EXCEPTION_FRAME_R17
+	swi r18, r1, MICROBLAZE_EXCEPTION_FRAME_R18
+	swi r19, r1, MICROBLAZE_EXCEPTION_FRAME_R19
+	swi r20, r1, MICROBLAZE_EXCEPTION_FRAME_R20
+	swi r21, r1, MICROBLAZE_EXCEPTION_FRAME_R21
+	swi r22, r1, MICROBLAZE_EXCEPTION_FRAME_R22
+	swi r23, r1, MICROBLAZE_EXCEPTION_FRAME_R23
+	swi r24, r1, MICROBLAZE_EXCEPTION_FRAME_R24
+	swi r25, r1, MICROBLAZE_EXCEPTION_FRAME_R25
+	swi r26, r1, MICROBLAZE_EXCEPTION_FRAME_R26
+	swi r27, r1, MICROBLAZE_EXCEPTION_FRAME_R27
+	swi r28, r1, MICROBLAZE_EXCEPTION_FRAME_R28
+	swi r29, r1, MICROBLAZE_EXCEPTION_FRAME_R29
+	swi r30, r1, MICROBLAZE_EXCEPTION_FRAME_R30
+	swi r31, r1, MICROBLAZE_EXCEPTION_FRAME_R31
+
+	/* Retrieve and store MSR */
+	mfs r3, rmsr
+	swi r3, r1, MICROBLAZE_EXCEPTION_FRAME_MSR
+
+	/* Retrieve and store EAR */
+	mfs r3, rear
+	swi r3, r1, MICROBLAZE_EXCEPTION_FRAME_EAR
+
+	/* Retrieve and store ESR */
+	mfs r3, resr
+	swi r3, r1, MICROBLAZE_EXCEPTION_FRAME_ESR
+
+	/* Retrieve and store BTR */
+	mfs r3, rbtr
+	swi r3, r1, MICROBLAZE_EXCEPTION_FRAME_BTR
+
+	/* Calculate and store original stack pointer */
+	addik r3, r1, CPU_EXCEPTION_FRAME_SIZE
+	swi r3, r1, MICROBLAZE_EXCEPTION_FRAME_R1
+
+	/* set parameter 1 to CPU Exception frame */
+	addi r5, r1, 0
+
+	/* call into the debug framework */
+	braid _MicroBlaze_Debug_handle
+	nop

bsps/microblaze/shared/start/start.S

@@ -46,7 +46,7 @@
 		# 0x14 #				Hardware Interrupt          _interrupt_handler
 
 		# 0x18 #				(-- IMM --)
-		# 0x1C #				Breakpoint Exception        (-- Don't Care --)
+		# 0x1C #				Breakpoint Exception        _debug_sw_break_handler
 
 		# 0x20 #				(-- IMM --)
 		# 0x24 #				Hardware Exception          _hw_exception_handler
@@ -73,6 +73,11 @@ _vector_sw_exception:
 _vector_interrupt:
 	brai _interrupt_handler
 
+	.section .vectors.debug_sw_break, "ax"
+	.align 2
+_vector_debug_sw_break:
+	brai _debug_sw_break_handler
+
 	.section .vectors.hw_exception, "ax"
 	.align 2
 _vector_hw_exception:

cpukit/score/cpu/microblaze/cpu.c

@@ -203,3 +203,29 @@ void _MicroBlaze_Exception_handle( CPU_Exception_frame *ef )
 
   rtems_fatal( RTEMS_FATAL_SOURCE_EXCEPTION, (rtems_fatal_code) ef );
 }
+
+MicroBlaze_Exception_handler installed_debug_handler = NULL;
+
+void _MicroBlaze_Debug_install_handler(
+  MicroBlaze_Exception_handler  new_handler,
+  MicroBlaze_Exception_handler *old_handler
+)
+{
+  if ( old_handler != NULL ) {
+    *old_handler = installed_debug_handler;
+  }
+
+  installed_debug_handler = new_handler;
+}
+
+void _MicroBlaze_Debug_handle( CPU_Exception_frame *ef )
+{
+  /* BiP is not set for software debug events, set it here */
+  ef->msr |= MICROBLAZE_MSR_BIP;
+
+  if ( installed_debug_handler != NULL ) {
+    installed_debug_handler( ef );
+  }
+
+  rtems_fatal( RTEMS_FATAL_SOURCE_EXCEPTION, (rtems_fatal_code) ef );
+}

cpukit/score/cpu/microblaze/include/rtems/score/cpu.h

@@ -344,6 +344,15 @@ void _MicroBlaze_Exception_handle(
   CPU_Exception_frame *ef
 );
 
+void _MicroBlaze_Debug_install_handler(
+  MicroBlaze_Exception_handler  new_handler,
+  MicroBlaze_Exception_handler *old_handler
+);
+
+void _MicroBlaze_Debug_handle(
+  CPU_Exception_frame *ef
+);
+
 void _CPU_Context_switch(
   Context_Control  *run,
   Context_Control  *heir

spec/build/bsps/microblaze/microblaze_fpga/obj.yml

@@ -25,6 +25,7 @@ source:
 - bsps/microblaze/microblaze_fpga/console/debug-io.c
 - bsps/microblaze/microblaze_fpga/fdt/bsp_fdt.c
 - bsps/microblaze/microblaze_fpga/irq/irq.c
+- bsps/microblaze/microblaze_fpga/start/_debug_sw_break_handler.S
 - bsps/microblaze/microblaze_fpga/start/_exception_handler.S
 - bsps/microblaze/microblaze_fpga/start/_interrupt_handler.S
 - bsps/microblaze/microblaze_fpga/start/bspreset.c