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bertos/cpu/dsp56k/hw/switch_dsp56k.c

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+/**
+ * \file
+ * <!--
+ * This file is part of BeRTOS.
+ *
+ * Bertos is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As a special exception, you may use this file as part of a free software
+ * library without restriction.  Specifically, if other files instantiate
+ * templates or use macros or inline functions from this file, or you compile
+ * this file and link it with other files to produce an executable, this
+ * file does not by itself cause the resulting executable to be covered by
+ * the GNU General Public License.  This exception does not however
+ * invalidate any other reasons why the executable file might be covered by
+ * the GNU General Public License.
+ *
+ * Copyright 2004, 2008 Develer S.r.l. (http://www.develer.com/)
+ * -->
+ *
+ * \author Giovanni Bajo <rasky@develer.com>
+ *
+ * \brief DSP5680x task switching support
+ */
+
+void asm_switch_context(void ** new_sp /* R2 */, void ** save_sp /* R3 */);
+asm void asm_switch_context(void ** new_sp, void ** save_sp)
+{
+	lea   (SP)+
+
+	; From the manual:
+	; The compiler uses page 0 address locations X: 0x0030 - 0x003F as register
+	; variables. Frequently accessed local variables are assigned to the page 0
+	; registers instead of to stack locations so that load and store instructions
+	; are shortened. Addresses X: 0x0030 - 0x0037 (page 0 registers MR0-MR7) are
+	; volatile registers and can be overwritten. The remaining registers (page 0
+	; registers MR8-MR15) are treated as non-volatile and, if used by a routine,
+	; must be saved on entry and restored on exit.
+	;
+	; So, register 0x30-0x37 are caller-save, while 0x38-0x3F are callee-save.
+	move  x:<$38,y1
+	move  y1,x:(SP)+
+	move  x:<$39,y1
+	move  y1,x:(SP)+
+	move  x:<$3A,y1
+	move  y1,x:(SP)+
+	move  x:<$3B,y1
+	move  y1,x:(SP)+
+	move  x:<$3C,y1
+	move  y1,x:(SP)+
+	move  x:<$3D,y1
+	move  y1,x:(SP)+
+	move  x:<$3E,y1
+	move  y1,x:(SP)+
+	move  x:<$3F,y1
+	move  y1,x:(SP)
+
+	;
+	; Switch stacks
+	nop
+	move SP, x:(R3)
+	nop
+	move x:(R2), SP
+	nop
+
+	;
+	; restore all saved registers
+	;
+	pop   y1
+	move  y1,x:<$3F
+	pop   y1
+	move  y1,x:<$3E
+	pop   y1
+	move  y1,x:<$3D
+	pop   y1
+	move  y1,x:<$3C
+	pop   y1
+	move  y1,x:<$3B
+	pop   y1
+	move  y1,x:<$3A
+	pop   y1
+	move  y1,x:<$39
+	pop   y1
+	move  y1,x:<$38
+
+	; SR is already pushed on the stack (normal call context). Use RTI to restore
+	; it, so that interrupt status is preserved across the tasks.
+	rti
+}