2 * arch/ppc/kernel/except_8xx.S
5 * Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
6 * Rewritten by Cort Dougan (cort@cs.nmt.edu) for PReP
7 * Copyright (C) 1996 Cort Dougan <cort@cs.nmt.edu>
8 * Low-level exception handlers and MMU support
9 * rewritten by Paul Mackerras.
10 * Copyright (C) 1996 Paul Mackerras.
11 * MPC8xx modifications by Dan Malek
12 * Copyright (C) 1997 Dan Malek (dmalek@jlc.net).
14 * This file contains low-level support and setup for PowerPC 8xx
15 * embedded processors, including trap and interrupt dispatch.
17 * This program is free software; you can redistribute it and/or
18 * modify it under the terms of the GNU General Public License
19 * as published by the Free Software Foundation; either version
20 * 2 of the License, or (at your option) any later version.
24 #include <linux/config.h>
25 #include <asm/processor.h>
28 #include <asm/cache.h>
29 #include <asm/pgtable.h>
30 #include <asm/cputable.h>
31 #include <asm/thread_info.h>
32 #include <asm/ppc_asm.h>
33 #include <asm/offsets.h>
35 /* Macro to make the code more readable. */
36 #ifdef CONFIG_8xx_CPU6
37 #define DO_8xx_CPU6(val, reg) \
42 #define DO_8xx_CPU6(val, reg)
52 * This port was done on an MBX board with an 860. Right now I only
53 * support an ELF compressed (zImage) boot from EPPC-Bug because the
54 * code there loads up some registers before calling us:
55 * r3: ptr to board info data
56 * r4: initrd_start or if no initrd then 0
57 * r5: initrd_end - unused if r4 is 0
58 * r6: Start of command line string
59 * r7: End of command line string
61 * I decided to use conditional compilation instead of checking PVR and
62 * adding more processor specific branches around code I don't need.
63 * Since this is an embedded processor, I also appreciate any memory
66 * The MPC8xx does not have any BATs, but it supports large page sizes.
67 * We first initialize the MMU to support 8M byte pages, then load one
68 * entry into each of the instruction and data TLBs to map the first
69 * 8M 1:1. I also mapped an additional I/O space 1:1 so we can get to
70 * the "internal" processor registers before MMU_init is called.
72 * The TLB code currently contains a major hack. Since I use the condition
73 * code register, I have to save and restore it. I am out of registers, so
74 * I just store it in memory location 0 (the TLB handlers are not reentrant).
75 * To avoid making any decisions, I need to use the "segment" valid bit
76 * in the first level table, but that would require many changes to the
77 * Linux page directory/table functions that I don't want to do right now.
79 * I used to use SPRG2 for a temporary register in the TLB handler, but it
80 * has since been put to other uses. I now use a hack to save a register
81 * and the CCR at memory location 0.....Someday I'll fix this.....
86 mr r31,r3 /* save parameters */
92 /* We have to turn on the MMU right away so we get cache modes
97 /* We now have the lower 8 Meg mapped into TLB entries, and the caches
103 ori r0,r0,MSR_DR|MSR_IR
106 ori r0,r0,start_here@l
109 rfi /* enables MMU */
112 * Exception entry code. This code runs with address translation
113 * turned off, i.e. using physical addresses.
114 * We assume sprg3 has the physical address of the current
115 * task's thread_struct.
117 #define EXCEPTION_PROLOG \
121 EXCEPTION_PROLOG_1; \
124 #define EXCEPTION_PROLOG_1 \
125 mfspr r11,SRR1; /* check whether user or kernel */ \
126 andi. r11,r11,MSR_PR; \
127 tophys(r11,r1); /* use tophys(r1) if kernel */ \
130 lwz r11,THREAD_INFO-THREAD(r11); \
131 addi r11,r11,THREAD_SIZE; \
133 1: subi r11,r11,INT_FRAME_SIZE /* alloc exc. frame */
136 #define EXCEPTION_PROLOG_2 \
138 stw r10,_CCR(r11); /* save registers */ \
139 stw r12,GPR12(r11); \
142 stw r10,GPR10(r11); \
144 stw r12,GPR11(r11); \
146 stw r10,_LINK(r11); \
151 tovirt(r1,r11); /* set new kernel sp */ \
152 li r10,MSR_KERNEL & ~(MSR_IR|MSR_DR); /* can take exceptions */ \
153 MTMSRD(r10); /* (except for mach check in rtas) */ \
155 SAVE_4GPRS(3, r11); \
159 * Note: code which follows this uses cr0.eq (set if from kernel),
160 * r11, r12 (SRR0), and r9 (SRR1).
162 * Note2: once we have set r1 we are in a position to take exceptions
163 * again, and we could thus set MSR:RI at that point.
169 #define EXCEPTION(n, label, hdlr, xfer) \
173 addi r3,r1,STACK_FRAME_OVERHEAD; \
176 #define EXC_XFER_TEMPLATE(n, hdlr, trap, copyee, tfer, ret) \
186 #define COPY_EE(d, s) rlwimi d,s,0,16,16
189 #define EXC_XFER_STD(n, hdlr) \
190 EXC_XFER_TEMPLATE(n, hdlr, n, NOCOPY, transfer_to_handler_full, \
191 ret_from_except_full)
193 #define EXC_XFER_LITE(n, hdlr) \
194 EXC_XFER_TEMPLATE(n, hdlr, n+1, NOCOPY, transfer_to_handler, \
197 #define EXC_XFER_EE(n, hdlr) \
198 EXC_XFER_TEMPLATE(n, hdlr, n, COPY_EE, transfer_to_handler_full, \
199 ret_from_except_full)
201 #define EXC_XFER_EE_LITE(n, hdlr) \
202 EXC_XFER_TEMPLATE(n, hdlr, n+1, COPY_EE, transfer_to_handler, \
206 EXCEPTION(0x100, Reset, UnknownException, EXC_XFER_STD)
216 addi r3,r1,STACK_FRAME_OVERHEAD
217 EXC_XFER_STD(0x200, MachineCheckException)
219 /* Data access exception.
220 * This is "never generated" by the MPC8xx. We jump to it for other
221 * translation errors.
230 EXC_XFER_EE_LITE(0x300, handle_page_fault)
232 /* Instruction access exception.
233 * This is "never generated" by the MPC8xx. We jump to it for other
234 * translation errors.
241 EXC_XFER_EE_LITE(0x400, handle_page_fault)
243 /* External interrupt */
244 EXCEPTION(0x500, HardwareInterrupt, do_IRQ, EXC_XFER_LITE)
246 /* Alignment exception */
254 addi r3,r1,STACK_FRAME_OVERHEAD
255 EXC_XFER_EE(0x600, AlignmentException)
257 /* Program check exception */
258 EXCEPTION(0x700, ProgramCheck, ProgramCheckException, EXC_XFER_STD)
260 /* No FPU on MPC8xx. This exception is not supposed to happen.
262 EXCEPTION(0x800, FPUnavailable, UnknownException, EXC_XFER_STD)
265 EXCEPTION(0x900, Decrementer, timer_interrupt, EXC_XFER_LITE)
267 EXCEPTION(0xa00, Trap_0a, UnknownException, EXC_XFER_EE)
268 EXCEPTION(0xb00, Trap_0b, UnknownException, EXC_XFER_EE)
274 EXC_XFER_EE_LITE(0xc00, DoSyscall)
276 /* Single step - not used on 601 */
277 EXCEPTION(0xd00, SingleStep, SingleStepException, EXC_XFER_STD)
278 EXCEPTION(0xe00, Trap_0e, UnknownException, EXC_XFER_EE)
279 EXCEPTION(0xf00, Trap_0f, UnknownException, EXC_XFER_EE)
281 /* On the MPC8xx, this is a software emulation interrupt. It occurs
282 * for all unimplemented and illegal instructions.
284 EXCEPTION(0x1000, SoftEmu, SoftwareEmulation, EXC_XFER_STD)
288 * For the MPC8xx, this is a software tablewalk to load the instruction
289 * TLB. It is modelled after the example in the Motorola manual. The task
290 * switch loads the M_TWB register with the pointer to the first level table.
291 * If we discover there is no second level table (the value is zero), the
292 * plan was to load that into the TLB, which causes another fault into the
293 * TLB Error interrupt where we can handle such problems. However, that did
294 * not work, so if we discover there is no second level table, we restore
295 * registers and branch to the error exception. We have to use the MD_xxx
296 * registers for the tablewalk because the equivalent MI_xxx registers
297 * only perform the attribute functions.
300 #ifdef CONFIG_8xx_CPU6
303 DO_8xx_CPU6(0x3f80, r3)
304 mtspr M_TW, r10 /* Save a couple of working registers */
308 mfspr r10, SRR0 /* Get effective address of fault */
309 DO_8xx_CPU6(0x3780, r3)
310 mtspr MD_EPN, r10 /* Have to use MD_EPN for walk, MI_EPN can't */
311 mfspr r10, M_TWB /* Get level 1 table entry address */
313 /* If we are faulting a kernel address, we have to use the
314 * kernel page tables.
316 andi. r11, r10, 0x0800 /* Address >= 0x80000000 */
318 lis r11, swapper_pg_dir@h
319 ori r11, r11, swapper_pg_dir@l
320 rlwimi r10, r11, 0, 2, 19
322 lwz r11, 0(r10) /* Get the level 1 entry */
323 rlwinm. r10, r11,0,0,19 /* Extract page descriptor page address */
324 beq 2f /* If zero, don't try to find a pte */
326 /* We have a pte table, so load the MI_TWC with the attributes
327 * for this "segment."
329 ori r11,r11,1 /* Set valid bit */
330 DO_8xx_CPU6(0x2b80, r3)
331 mtspr MI_TWC, r11 /* Set segment attributes */
332 DO_8xx_CPU6(0x3b80, r3)
333 mtspr MD_TWC, r11 /* Load pte table base address */
334 mfspr r11, MD_TWC /* ....and get the pte address */
335 lwz r10, 0(r11) /* Get the pte */
337 ori r10, r10, _PAGE_ACCESSED
340 /* The Linux PTE won't go exactly into the MMU TLB.
341 * Software indicator bits 21, 22 and 28 must be clear.
342 * Software indicator bits 24, 25, 26, and 27 must be
343 * set. All other Linux PTE bits control the behavior
347 rlwimi r10, r11, 0, 24, 28 /* Set 24-27, clear 28 */
348 DO_8xx_CPU6(0x2d80, r3)
349 mtspr MI_RPN, r10 /* Update TLB entry */
351 mfspr r10, M_TW /* Restore registers */
355 #ifdef CONFIG_8xx_CPU6
360 2: mfspr r10, M_TW /* Restore registers */
364 #ifdef CONFIG_8xx_CPU6
371 #ifdef CONFIG_8xx_CPU6
374 DO_8xx_CPU6(0x3f80, r3)
375 mtspr M_TW, r10 /* Save a couple of working registers */
379 mfspr r10, M_TWB /* Get level 1 table entry address */
381 /* If we are faulting a kernel address, we have to use the
382 * kernel page tables.
384 andi. r11, r10, 0x0800
386 lis r11, swapper_pg_dir@h
387 ori r11, r11, swapper_pg_dir@l
388 rlwimi r10, r11, 0, 2, 19
390 lwz r11, 0(r10) /* Get the level 1 entry */
391 rlwinm. r10, r11,0,0,19 /* Extract page descriptor page address */
392 beq 2f /* If zero, don't try to find a pte */
394 /* We have a pte table, so load fetch the pte from the table.
396 ori r11, r11, 1 /* Set valid bit in physical L2 page */
397 DO_8xx_CPU6(0x3b80, r3)
398 mtspr MD_TWC, r11 /* Load pte table base address */
399 mfspr r10, MD_TWC /* ....and get the pte address */
400 lwz r10, 0(r10) /* Get the pte */
402 /* Insert the Guarded flag into the TWC from the Linux PTE.
403 * It is bit 27 of both the Linux PTE and the TWC (at least
404 * I got that right :-). It will be better when we can put
405 * this into the Linux pgd/pmd and load it in the operation
408 rlwimi r11, r10, 0, 27, 27
409 DO_8xx_CPU6(0x3b80, r3)
412 mfspr r11, MD_TWC /* get the pte address again */
413 ori r10, r10, _PAGE_ACCESSED
416 /* The Linux PTE won't go exactly into the MMU TLB.
417 * Software indicator bits 21, 22 and 28 must be clear.
418 * Software indicator bits 24, 25, 26, and 27 must be
419 * set. All other Linux PTE bits control the behavior
423 rlwimi r10, r11, 0, 24, 28 /* Set 24-27, clear 28 */
424 DO_8xx_CPU6(0x3d80, r3)
425 mtspr MD_RPN, r10 /* Update TLB entry */
427 mfspr r10, M_TW /* Restore registers */
431 #ifdef CONFIG_8xx_CPU6
436 2: mfspr r10, M_TW /* Restore registers */
440 #ifdef CONFIG_8xx_CPU6
445 /* This is an instruction TLB error on the MPC8xx. This could be due
446 * to many reasons, such as executing guarded memory or illegal instruction
447 * addresses. There is nothing to do but handle a big time error fault.
453 /* This is the data TLB error on the MPC8xx. This could be due to
454 * many reasons, including a dirty update to a pte. We can catch that
455 * one here, but anything else is an error. First, we track down the
456 * Linux pte. If it is valid, write access is allowed, but the
457 * page dirty bit is not set, we will set it and reload the TLB. For
458 * any other case, we bail out to a higher level function that can
463 #ifdef CONFIG_8xx_CPU6
466 DO_8xx_CPU6(0x3f80, r3)
467 mtspr M_TW, r10 /* Save a couple of working registers */
472 /* First, make sure this was a store operation.
475 andis. r11, r10, 0x0200 /* If set, indicates store op */
478 /* The EA of a data TLB miss is automatically stored in the MD_EPN
479 * register. The EA of a data TLB error is automatically stored in
480 * the DAR, but not the MD_EPN register. We must copy the 20 most
481 * significant bits of the EA from the DAR to MD_EPN before we
482 * start walking the page tables. We also need to copy the CASID
483 * value from the M_CASID register.
484 * Addendum: The EA of a data TLB error is _supposed_ to be stored
485 * in DAR, but it seems that this doesn't happen in some cases, such
486 * as when the error is due to a dcbi instruction to a page with a
487 * TLB that doesn't have the changed bit set. In such cases, there
488 * does not appear to be any way to recover the EA of the error
489 * since it is neither in DAR nor MD_EPN. As a workaround, the
490 * _PAGE_HWWRITE bit is set for all kernel data pages when the PTEs
491 * are initialized in mapin_ram(). This will avoid the problem,
492 * assuming we only use the dcbi instruction on kernel addresses.
495 rlwinm r11, r10, 0, 0, 19
496 ori r11, r11, MD_EVALID
498 rlwimi r11, r10, 0, 28, 31
499 DO_8xx_CPU6(0x3780, r3)
502 mfspr r10, M_TWB /* Get level 1 table entry address */
504 /* If we are faulting a kernel address, we have to use the
505 * kernel page tables.
507 andi. r11, r10, 0x0800
509 lis r11, swapper_pg_dir@h
510 ori r11, r11, swapper_pg_dir@l
511 rlwimi r10, r11, 0, 2, 19
513 lwz r11, 0(r10) /* Get the level 1 entry */
514 rlwinm. r10, r11,0,0,19 /* Extract page descriptor page address */
515 beq 2f /* If zero, bail */
517 /* We have a pte table, so fetch the pte from the table.
519 ori r11, r11, 1 /* Set valid bit in physical L2 page */
520 DO_8xx_CPU6(0x3b80, r3)
521 mtspr MD_TWC, r11 /* Load pte table base address */
522 mfspr r11, MD_TWC /* ....and get the pte address */
523 lwz r10, 0(r11) /* Get the pte */
525 andi. r11, r10, _PAGE_RW /* Is it writeable? */
526 beq 2f /* Bail out if not */
528 /* Update 'changed', among others.
530 ori r10, r10, _PAGE_DIRTY|_PAGE_ACCESSED|_PAGE_HWWRITE
531 mfspr r11, MD_TWC /* Get pte address again */
532 stw r10, 0(r11) /* and update pte in table */
534 /* The Linux PTE won't go exactly into the MMU TLB.
535 * Software indicator bits 21, 22 and 28 must be clear.
536 * Software indicator bits 24, 25, 26, and 27 must be
537 * set. All other Linux PTE bits control the behavior
541 rlwimi r10, r11, 0, 24, 28 /* Set 24-27, clear 28 */
542 DO_8xx_CPU6(0x3d80, r3)
543 mtspr MD_RPN, r10 /* Update TLB entry */
545 mfspr r10, M_TW /* Restore registers */
549 #ifdef CONFIG_8xx_CPU6
554 mfspr r10, M_TW /* Restore registers */
558 #ifdef CONFIG_8xx_CPU6
563 EXCEPTION(0x1500, Trap_15, UnknownException, EXC_XFER_EE)
564 EXCEPTION(0x1600, Trap_16, UnknownException, EXC_XFER_EE)
565 EXCEPTION(0x1700, Trap_17, UnknownException, EXC_XFER_EE)
566 EXCEPTION(0x1800, Trap_18, UnknownException, EXC_XFER_EE)
567 EXCEPTION(0x1900, Trap_19, UnknownException, EXC_XFER_EE)
568 EXCEPTION(0x1a00, Trap_1a, UnknownException, EXC_XFER_EE)
569 EXCEPTION(0x1b00, Trap_1b, UnknownException, EXC_XFER_EE)
571 /* On the MPC8xx, these next four traps are used for development
572 * support of breakpoints and such. Someday I will get around to
575 EXCEPTION(0x1c00, Trap_1c, UnknownException, EXC_XFER_EE)
576 EXCEPTION(0x1d00, Trap_1d, UnknownException, EXC_XFER_EE)
577 EXCEPTION(0x1e00, Trap_1e, UnknownException, EXC_XFER_EE)
578 EXCEPTION(0x1f00, Trap_1f, UnknownException, EXC_XFER_EE)
587 * This is where the main kernel code starts.
592 ori r2,r2,init_task@l
594 /* ptr to phys current thread */
596 addi r4,r4,THREAD /* init task's THREAD */
599 mtspr SPRG2,r3 /* 0 => r1 has kernel sp */
602 lis r1,init_thread_union@ha
603 addi r1,r1,init_thread_union@l
605 stwu r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
607 bl early_init /* We have to do this with MMU on */
610 * Decide what sort of machine this is and initialize the MMU.
621 * Go back to running unmapped so we can load up new values
622 * and change to using our exception vectors.
623 * On the 8xx, all we have to do is invalidate the TLB to clear
624 * the old 8M byte TLB mappings and load the page table base register.
626 /* The right way to do this would be to track it down through
627 * init's THREAD like the context switch code does, but this is
628 * easier......until someone changes init's static structures.
630 lis r6, swapper_pg_dir@h
631 ori r6, r6, swapper_pg_dir@l
633 #ifdef CONFIG_8xx_CPU6
634 lis r4, cpu6_errata_word@h
635 ori r4, r4, cpu6_errata_word@l
644 li r3,MSR_KERNEL & ~(MSR_IR|MSR_DR)
648 /* Load up the kernel context */
650 SYNC /* Force all PTE updates to finish */
651 tlbia /* Clear all TLB entries */
652 sync /* wait for tlbia/tlbie to finish */
653 TLBSYNC /* ... on all CPUs */
655 /* set up the PTE pointers for the Abatron bdiGDB.
658 lis r5, abatron_pteptrs@h
659 ori r5, r5, abatron_pteptrs@l
660 stw r5, 0xf0(r0) /* Must match your Abatron config file */
664 /* Now turn on the MMU for real! */
666 lis r3,start_kernel@h
667 ori r3,r3,start_kernel@l
670 rfi /* enable MMU and jump to start_kernel */
672 /* Set up the initial MMU state so we can do the first level of
673 * kernel initialization. This maps the first 8 MBytes of memory 1:1
674 * virtual to physical. Also, set the cache mode since that is defined
675 * by TLB entries and perform any additional mapping (like of the IMMR).
676 * If configured to pin some TLBs, we pin the first 8 Mbytes of kernel,
677 * 24 Mbytes of data, and the 8M IMMR space. Anything not covered by
678 * these mappings is mapped by page tables.
681 tlbia /* Invalidate all TLB entries */
682 #ifdef CONFIG_PIN_TLB
688 mtspr MI_CTR, r8 /* Set instruction MMU control */
690 #ifdef CONFIG_PIN_TLB
691 lis r10, (MD_RSV4I | MD_RESETVAL)@h
695 lis r10, MD_RESETVAL@h
697 #ifndef CONFIG_8xx_COPYBACK
698 oris r10, r10, MD_WTDEF@h
700 mtspr MD_CTR, r10 /* Set data TLB control */
702 /* Now map the lower 8 Meg into the TLBs. For this quick hack,
703 * we can load the instruction and data TLB registers with the
706 lis r8, KERNELBASE@h /* Create vaddr for TLB */
707 ori r8, r8, MI_EVALID /* Mark it valid */
710 li r8, MI_PS8MEG /* Set 8M byte page */
711 ori r8, r8, MI_SVALID /* Make it valid */
714 li r8, MI_BOOTINIT /* Create RPN for address 0 */
715 mtspr MI_RPN, r8 /* Store TLB entry */
717 lis r8, MI_Kp@h /* Set the protection mode */
721 /* Map another 8 MByte at the IMMR to get the processor
722 * internal registers (among other things).
724 #ifdef CONFIG_PIN_TLB
725 addi r10, r10, 0x0100
728 mfspr r9, 638 /* Get current IMMR */
729 andis. r9, r9, 0xff80 /* Get 8Mbyte boundary */
731 mr r8, r9 /* Create vaddr for TLB */
732 ori r8, r8, MD_EVALID /* Mark it valid */
734 li r8, MD_PS8MEG /* Set 8M byte page */
735 ori r8, r8, MD_SVALID /* Make it valid */
737 mr r8, r9 /* Create paddr for TLB */
738 ori r8, r8, MI_BOOTINIT|0x2 /* Inhibit cache -- Cort */
741 #ifdef CONFIG_PIN_TLB
742 /* Map two more 8M kernel data pages.
744 addi r10, r10, 0x0100
747 lis r8, KERNELBASE@h /* Create vaddr for TLB */
748 addis r8, r8, 0x0080 /* Add 8M */
749 ori r8, r8, MI_EVALID /* Mark it valid */
751 li r9, MI_PS8MEG /* Set 8M byte page */
752 ori r9, r9, MI_SVALID /* Make it valid */
754 li r11, MI_BOOTINIT /* Create RPN for address 0 */
755 addis r11, r11, 0x0080 /* Add 8M */
758 addis r8, r8, 0x0080 /* Add 8M */
761 addis r11, r11, 0x0080 /* Add 8M */
765 /* Since the cache is enabled according to the information we
766 * just loaded into the TLB, invalidate and enable the caches here.
767 * We should probably check/set other modes....later.
774 #ifdef CONFIG_8xx_COPYBACK
777 /* For a debug option, I left this here to easily enable
778 * the write through cache mode
789 * Set up to use a given MMU context.
790 * r3 is context number, r4 is PGD pointer.
792 * We place the physical address of the new task page directory loaded
793 * into the MMU base register, and set the ASID compare register with
798 #ifdef CONFIG_BDI_SWITCH
799 /* Context switch the PTE pointer for the Abatron BDI2000.
800 * The PGDIR is passed as second argument.
807 #ifdef CONFIG_8xx_CPU6
808 lis r6, cpu6_errata_word@h
809 ori r6, r6, cpu6_errata_word@l
814 mtspr M_TWB, r4 /* Update MMU base address */
818 mtspr M_CASID, r3 /* Update context */
820 mtspr M_CASID,r3 /* Update context */
822 mtspr M_TWB, r4 /* and pgd */
827 #ifdef CONFIG_8xx_CPU6
828 /* It's here because it is unique to the 8xx.
829 * It is important we get called with interrupts disabled. I used to
830 * do that, but it appears that all code that calls this already had
831 * interrupt disabled.
835 lis r7, cpu6_errata_word@h
836 ori r7, r7, cpu6_errata_word@l
840 mtspr 22, r3 /* Update Decrementer */
846 * We put a few things here that have to be page-aligned.
847 * This stuff goes at the beginning of the data segment,
848 * which is page-aligned.
853 .globl empty_zero_page
857 .globl swapper_pg_dir
862 * This space gets a copy of optional info passed to us by the bootstrap
863 * Used to pass parameters into the kernel like root=/dev/sda1, etc.
869 /* Room for two PTE table poiners, usually the kernel and current user
870 * pointer to their respective root page table (pgdir).
875 #ifdef CONFIG_8xx_CPU6
876 .globl cpu6_errata_word