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source: trunk/softs/giet_tsar/giet.s @ 337

Last change on this file since 337 was 158, checked in by alain, 13 years ago

Introducing the three sub-directories in the softs directory:

giet_tsar
soft_filter_giet
soft_transpose_giet

File size: 31.5 KB

Rev	Line
[158]	1	/*********************************************************************************
	2	* File : giet.s
	3	* Author : Franck Wajsburt & Alain Greiner & Joel Porquet
	4	* Date : 2009 - 2010
	5	**********************************************************************************
	6	* Interruption/Exception/Trap Handler for MIPS32 processor
	7	* The base address of the segment containing this code
	8	* MUST be 0x80000000, in order to have the entry point
	9	* at address 0x80000180 !!!
	10	* All messages are printed on the TTY defined by the processor ID.
	11	**********************************************************************************
	12	* History :
	13	* 15/09/2009 : The GIET entry point has been modified to comply with
	14	* the MIPS32 specification : 0x80000180
	15	* 5/10/2009 : The syscall handler has been modified to comply with the
	16	* MIPS32 specification : the value stored in EPC register is the
	17	* syscall instruction address => it must be incremented by 4
	18	* to obtain the return address.
	19	* 15/10/2009 : The Interrupt handler has been modified to comply with the
	20	* VCI_ICU specification : The IRQ index is obtained by a read
	21	* to (icu_base_address + 16).
	22	* 26/10/2009 : The interrupt handler has been modified to support
	23	* multi-processors architectures with one ICU per processor.
	24	* Finally, the mfc0 instruction uses now the select parameter
	25	* to comply with the MIPS32 specification when accessing the
	26	* processor_id (mtfc0 $x, $15, 1)
	27	* 08/11/2009 : The syscall handler has been extended to support 32 values
	28	* for the syscall index, and to enable interrupts when processing
	29	* a system call.
	30	* Five new syscalls have been introduced to access the frame buffer
	31	* Three new syscalls have been introduced to access the block device
	32	* The two syscalls associated to the DMA have been removed.
	33	* 18/11/2009 : The syscall handler has been modified to save the SR in
	34	* the stack before enabling interrupts.
	35	* 15/03/2010 : replace the itoa_print assembler function by the itoa_hex()
	36	* function defined in the syscalls.c file.
	37	* 10/04/2010 : modify the interrupt handler to use the new ICU component
	38	* supporting up to 8 output IRQs for 8 processors.
	39	* The active IRQ index is obtained as ICU[32*PROC_ID+16].
	40	* 12/09/2010 : The ctx_switch functionhas been included in this file to
	41	* simplify the compilation process.
	42	* 25/09/2010 : add '.end' directive to end the _giet function
	43	* and modify the 'sharp' comment character into the regular "slash
	44	* asterix ... asterix slash" comment syntax
	45	* 27/09/2010 : respect stack convention with 4 minimum slots before calling
	46	* C functions
	47	* 28/09/2010 : Save all the non-persistant registers in the int_handler
	48	* 02/02/2011 : Introduce the "segment_increment" parameter in the interrupt
	49	* handler to support clusterised multi-processing.
	50	* Introducing the barrier_init() & barrier_wait() system calls.
	51	* 04/04/2011 : introducing the system call proc_num()
	52	* 12/04/2011 : modifying the _int_handler to support the XICU component in
	53	* multi_clusters/multi-processors architectures:
	54	* the XICU base address depends the cluster_id and the PRIO register
	55	* address depends on the local_id.
	56	**********************************************************************************/
	57
	58	.section .giet,"ax",@progbits
	59	.align 2
	60	.global _interrupt_vector # makes interrupt_vector an external symbol
	61
	62	.extern seg_icu_base
	63	.extern seg_tty_base
	64	.extern NB_CLUSTERS
	65	.extern NB_PROCS
	66
	67	.extern isr_default
	68
	69	.extern _procid
	70	.extern _proctime
	71	.extern _tty_write
	72	.extern _tty_read
	73	.extern _tty_read_irq
	74	.extern _timer_write
	75	.extern _timer_read
	76	.extern _icu_write
	77	.extern _icu_read
	78	.extern _gcd_write
	79	.extern _gcd_read
	80	.extern _locks_read
	81	.extern _locks_write
	82	.extern _exit
	83	.extern _fb_sync_write
	84	.extern _fb_sync_read
	85	.extern _fb_write
	86	.extern _fb_read
	87	.extern _fb_completed
	88	.extern _ioc_write
	89	.extern _ioc_read
	90	.extern _ioc_completed
	91	.extern _itoa_hex
	92	.extern _barrier_init
	93	.extern _barrier_wait
	94
	95	.ent _giet
	96
	97	/***************************************************************
	98	* Cause Table (indexed by the Cause register)
	99	***************************************************************/
	100	tab_causes:
	101	.word _int_handler # 0000 : external interrupt
	102	.word _cause_ukn # 0001 : undefined exception
	103	.word _cause_ukn # 0010 : undefined exception
	104	.word _cause_ukn # 0011 : undefined exception
	105	.word _cause_adel # 0100 : illegal address read exception
	106	.word _cause_ades # 0101 : illegal address write exception
	107	.word _cause_ibe # 0110 : instruction bus error exception
	108	.word _cause_dbe # 0111 : data bus error exception
	109	.word _sys_handler # 1000 : system call
	110	.word _cause_bp # 1001 : breakpoint exception
	111	.word _cause_ri # 1010 : illegal codop exception
	112	.word _cause_cpu # 1011 : illegal coprocessor access
	113	.word _cause_ovf # 1100 : arithmetic overflow exception
	114	.word _cause_ukn # 1101 : undefined exception
	115	.word _cause_ukn # 1110 : undefined exception
	116	.word _cause_ukn # 1111 : undefined exception
	117
	118	.space 320
	119
	120	/***************************************************************
	121	* Entry point (at address 0x80000180)
	122	***************************************************************/
	123	_giet:
	124	mfc0 $27, $13 # Cause Register analysis
	125	lui $26, 0x8000 # $26 <= tab_causes
	126	andi $27, $27, 0x3c
	127	addu $26, $26, $27
	128	lw $26, ($26)
	129	jr $26 # Jump indexed by CR
	130	.end _giet
	131
	132	/****************************************************************
	133	* System Call Handler
	134	* A system call is handled as a special function call.
	135	* - $2 contains the system call index (< 16).
	136	* - $3 is used to store the syscall address
	137	* - $4, $5, $6, $7 contain the arguments values.
	138	* - The return address (EPC) iand the SR are saved in the stack.
	139	* - Interrupts are enabled before branching to the syscall.
	140	* - All syscalls must return to the syscall handler.
	141	* - $2, $3, $4, $5, $6, $7 as well as $26 & $27 can be modified.
	142	*
	143	* In case of undefined system call, an error message displays
	144	* the value of EPC on the TTY corresponding to the processor,
	145	* and the user program is killed.
	146	****************************************************************/
	147	_sys_handler:
	148	addiu $29, $29, -24 # 2 slots for SR&EPC, 4 slots for args passing
	149	mfc0 $26, $12 # load SR
	150	sw $26, 16($29) # save it in the stack
	151	mfc0 $27, $14 # load EPC
	152	addiu $27, $27, 4 # increment EPC for return address
	153	sw $27, 20($29) # save it in the stack
	154
	155	andi $26, $2, 0x1F # $26 <= syscall index (i < 32)
	156	sll $26, $26, 2 # $26 <= index * 4
	157	la $27, tab_syscalls # $27 <= &tab_syscalls[0]
	158	addu $27, $27, $26 # $27 <= &tab_syscalls[i]
	159	lw $3, 0($27) # $3 <= syscall address
	160
	161	li $27, 0xFFFFFFED # Mask for UM & EXL bits
	162	mfc0 $26, $12 # $26 <= SR
	163	and $26, $26, $27 # UM = 0 / EXL = 0
	164	mtc0 $26, $12 # interrupt enabled
	165	jalr $3 # jump to the proper syscall
	166	mtc0 $0, $12 # interrupt disbled
	167
	168	lw $26, 16($29) # load SR from stack
	169	mtc0 $26, $12 # restore SR
	170	lw $26, 20($29) # load EPC from stack
	171	mtc0 $26, $14 # restore EPC
	172	addiu $29, $29, 24 # restore stack pointer
	173	eret # exit GIET
	174
	175	_sys_ukn: # undefined system call
	176	la $4, msg_uknsyscall # $4 <= message address
	177	li $5, 36 # $5 <= message length
	178	jal _tty_write # print unknown message
	179
	180	la $4, msg_epc # $4 <= message address
	181	li $5, 8 # $5 <= message length
	182	jal _tty_write # print EPC message
	183
	184	mfc0 $4, $14 # $4 <= EPC
	185	la $5, itoa_buffer # $5 <= buffer address
	186	addiu $5, $5, 2 # skip the 0x prefix
	187	jal _itoa_hex # fill the buffer
	188
	189	la $4, itoa_buffer # $4 <= buffer address
	190	li $5, 10 # $5 <= buffer length
	191	jal _tty_write # print EPC value
	192
	193	j _exit # end of program
	194
	195	itoa_buffer: .ascii "0x00000000"
	196
	197	.align 2
	198
	199	/****************************************************************
	200	* System Call Table (indexed by syscall index)
	201	****************************************************************/
	202	tab_syscalls:
	203	.word _procid # 0x00
	204	.word _proctime # 0x01
	205	.word _tty_write # 0x02
	206	.word _tty_read # 0x03
	207	.word _timer_write # 0x04
	208	.word _timer_read # 0x05
	209	.word _gcd_write # 0x06
	210	.word _gcd_read # 0x07
	211	.word _icu_write # 0x08
	212	.word _icu_read # 0x09
	213	.word _tty_read_irq # 0x0A
	214	.word _sys_ukn # 0x0B
	215	.word _locks_write # 0x0C
	216	.word _locks_read # 0x0D
	217	.word _exit # 0x0E
	218	.word _procnumber # 0x0F
	219	.word _fb_sync_write # 0x10
	220	.word _fb_sync_read # 0x11
	221	.word _fb_write # 0x12
	222	.word _fb_read # 0x13
	223	.word _fb_completed # 0x14
	224	.word _ioc_write # 0x15
	225	.word _ioc_read # 0x16
	226	.word _ioc_completed # 0x17
	227	.word _barrier_init # 0x18
	228	.word _barrier_wait # 0x19
	229	.word _sys_ukn # 0x1A
	230	.word _sys_ukn # 0x1B
	231	.word _sys_ukn # 0x1C
	232	.word _sys_ukn # 0x1D
	233	.word _sys_ukn # 0x1E
	234	.word _sys_ukn # 0x1F
	235
	236	/******************************************************************
	237	* Interrupt Handler
	238	* This simple interrupt handler cannot be interrupted.
	239	* It uses an external ICU component (Interrupt Controler Unit)
	240	* that concentrates up to 32 interrupts lines to a single IRQ
	241	* line that can be connected to any of the 6 MIPS IT inputs.
	242	* This component returns the highest priority active interrupt index
	243	* (smaller indexes have the highest priority).
	244	*
	245	* In case of a multi-clusters architecture, it exist one ICU
	246	* per cluster. The base address of the ICU segment depends on both
	247	* the cluster_id and the proc_id:
	248	* - icu_base_address = seg_icu_base + (32 * local_id) +
	249	* (cluster_increment * cluster _id)
	250	* - cluster_id = proc_id / NB_PROCS
	251	* - local_id = proc_id % NB_PROCS
	252	* - cluster_increment = 4G / NB_CLUSTERS
	253	*
	254	* The interrupt handler reads the XICU PRIO register,
	255	* using the offset 16.
	256	* This component returns the highest priority interrupt index
	257	* (smaller indexes have the highest priority).
	258	* Any value larger than 31 means "no active interrupt", and
	259	* the default ISR (that does nothing) is executed.
	260	* The interrupt vector (32 ISR addresses array stored at
	261	* _interrupt_vector address) is initialised with the default
	262	* ISR address. The actual ISR addresses are supposed to be written
	263	* in the interrupt vector array by the boot code.
	264	* All non persistant registers, such as $1 to $15, and $24 to $25,
	265	* as well as register $31 and EPC, are saved in the interrupted
	266	* program stack, before calling the Interrupt Service Routine.
	267	* These registers can be used by the ISR code.
	268	*******************************************************************/
	269	_int_handler:
	270	addiu $29, $29, -23*4 # stack space reservation
	271	.set noat
	272	sw $1, 4*4($29) # save $1
	273	.set at
	274	sw $2, 4*5($29) # save $2
	275	sw $3, 4*6($29) # save $3
	276	sw $4, 4*7($29) # save $4
	277	sw $5, 4*8($29) # save $5
	278	sw $6, 4*9($29) # save $6
	279	sw $7, 4*10($29) # save $7
	280	sw $8, 4*11($29) # save $8
	281	sw $9, 4*12($29) # save $9
	282	sw $10, 4*13($29) # save $10
	283	sw $11, 4*14($29) # save $11
	284	sw $12, 4*15($29) # save $12
	285	sw $13, 4*16($29) # save $13
	286	sw $14, 4*17($29) # save $14
	287	sw $15, 4*18($29) # save $15
	288	sw $24, 4*19($29) # save $24
	289	sw $25, 4*20($29) # save $25
	290	sw $31, 4*21($29) # save $31
	291	mfc0 $27, $14
	292	sw $27, 4*22($29) # save EPC
	293
	294	# XICU PRIO register address computation (depending on cluster_id & local_id)
	295	mfc0 $10, $15, 1 # $10 <= proc_id
	296	andi $10, $10, 0x3FF # at most 1024 processors
	297	la $11, NB_PROCS # $11 <= NB_PROCS
	298	divu $10, $11
	299	mflo $12 # $12 <= cluster_id
	300	mfhi $13 # $13 <= local_id
	301	la $11, NB_CLUSTERS # $11 <= NB_CLUSTERS
	302	li $14, 0x80000000
	303	divu $14, $11
	304	mflo $15
	305	sll $15, $15, 1 # $15 <= cluster_increment = 4G / NB_CLUSTERS
	306	multu $15, $12
	307	mflo $6 # $6 <= cluster_increment * cluster_id
	308	li $7, 0b011110000000 # $7 <= PRIO offset
	309	sll $8, $13, 2 # $8 <= local_id*4
	310	addu $9, $7, $8 # $9 <= PRIO offset + local_id*4
	311	la $27, seg_icu_base
	312	addu $26, $9, $27 # $26 <= seg_icu_base + PRIO offset + local_id*4
	313	addu $26, $26, $6 # $26 <= seg_icu_base + incrementcluster_id + PRIO offset + local_id4
	314
	315	# XICU access and interrupt vector access
	316	lw $26, ($26) # $26 <= PRIO register value
	317	andi $27, $26, 0x2 # test bit HWI active
	318	beq $27, $0, restore # do nothing if no active IRQ
	319	srl $26, $26, 14 # $26 <= $26 >> 14
	320	andi $26, $26, 0x7C # $26 <= interrupt_index * 4
	321	la $27, _interrupt_vector
	322	addu $26, $26, $27
	323	lw $26, ($26) # read ISR address
	324	jalr $26 # call ISR
	325	restore:
	326	.set noat
	327	lw $1, 4*4($29) # restore $1
	328	.set at
	329	lw $2, 4*5($29) # restore $2
	330	lw $3, 4*6($29) # restore $3
	331	lw $4, 4*7($29) # restore $4
	332	lw $5, 4*8($29) # restore $5
	333	lw $6, 4*9($29) # restore $6
	334	lw $7, 4*10($29) # restore $7
	335	lw $8, 4*11($29) # restore $8
	336	lw $9, 4*12($29) # restore $9
	337	lw $10, 4*13($29) # restore $10
	338	lw $11, 4*14($29) # restore $11
	339	lw $12, 4*15($29) # restore $12
	340	lw $13, 4*16($29) # restore $13
	341	lw $14, 4*17($29) # restore $14
	342	lw $15, 4*18($29) # restore $15
	343	lw $24, 4*19($29) # restore $24
	344	lw $25, 4*20($29) # restore $25
	345	lw $31, 4*21($29) # restore $31
	346	lw $27, 4*22($29) # return address (EPC)
	347	addiu $29, $29, 23*4 # restore stack pointer
	348	mtc0 $27, $14 # restore EPC
	349	eret # exit GIET
	350
	351	/* The default ISR is called when no specific ISR has been installed in the
	352	interrupt vector. It simply displays a message on TTY 0. */
	353
	354	isr_default:
	355	addiu $29, $29, -20 # get space in stack
	356	sw $31, 16($29) # to save the return address
	357	la $4, msg_default # $4 <= string address
	358	addi $5, $0, 36 # $5 <= string length
	359	jal _tty_write # print
	360	lw $31, 16($29) # restore return address
	361	addiu $29, $29, 20 # free space
	362	jr $31 # returns to interrupt handler
	363
	364	/*****************************************************
	365	Interrupt Vector Table (indexed by interrupt index)
	366	32 words corresponding to 32 ISR addresses
	367	******************************************************/
	368	_interrupt_vector:
	369	.word isr_default # ISR 0
	370	.word isr_default # ISR 1
	371	.word isr_default # ISR 2
	372	.word isr_default # ISR 3
	373	.word isr_default # ISR 4
	374	.word isr_default # ISR 5
	375	.word isr_default # ISR 6
	376	.word isr_default # ISR 7
	377	.word isr_default # ISR 8
	378	.word isr_default # ISR 9
	379	.word isr_default # ISR 10
	380	.word isr_default # ISR 11
	381	.word isr_default # ISR 12
	382	.word isr_default # ISR 13
	383	.word isr_default # ISR 14
	384	.word isr_default # ISR 15
	385	.word isr_default # ISR 16
	386	.word isr_default # ISR 17
	387	.word isr_default # ISR 18
	388	.word isr_default # ISR 19
	389	.word isr_default # ISR 20
	390	.word isr_default # ISR 21
	391	.word isr_default # ISR 22
	392	.word isr_default # ISR 23
	393	.word isr_default # ISR 24
	394	.word isr_default # ISR 25
	395	.word isr_default # ISR 26
	396	.word isr_default # ISR 27
	397	.word isr_default # ISR 28
	398	.word isr_default # ISR 29
	399	.word isr_default # ISR 30
	400	.word isr_default # ISR 31
	401
	402	/***********************************************************
	403	* Exception Handler
	404	* Same code for all fatal exceptions :
	405	* Print the exception type and the values of EPC & BAR
	406	* on the TTY correspondintg to the processor PROCID,
	407	* and the user program is killed.
	408	***********************************************************/
	409	_cause_bp:
	410	_cause_ukn:
	411	_cause_ri:
	412	_cause_ovf:
	413	_cause_adel:
	414	_cause_ades:
	415	_cause_ibe:
	416	_cause_dbe:
	417	_cause_cpu:
	418	mfc0 $26, $13 # $26 <= CR
	419	andi $26, $26, 0x3C # $26 <= _cause_index * 4
	420	la $27, mess_causes # mess_cause table base address
	421	addu $27, $26, $27 # pointer on the message base address
	422
	423	lw $4, ($27) # $4 <= message address
	424	li $5, 36 # $5 <= message length
	425	jal _tty_write # print message cause
	426
	427	la $4, msg_epc # $4 <= message address
	428	li $5, 8 # $5 <= message length
	429	jal _tty_write # print message EPC
	430
	431	mfc0 $4, $14 # $4 <= EPC value
	432	la $5, itoa_buffer # $5 <= buffer address
	433	addiu $5, $5, 2 # skip 0x prefix
	434	jal _itoa_hex # fill buffer
	435
	436	la $4, itoa_buffer # $4 <= buffer address
	437	li $5, 10 # $5 <= buffer length
	438	jal _tty_write # print EPC value
	439
	440	la $4, msg_bar # $4 <= mesage address
	441	li $5, 8 # $5 <= message length
	442	jal _tty_write # print message BAR
	443
	444	mfc0 $4, $8 # $4 <= BAR value
	445	la $5, itoa_buffer # $5 <= buffer address
	446	addiu $5, $5, 2 # skip 0x prefix
	447	jal _itoa_hex # fill buffer
	448
	449	la $4, itoa_buffer # $4 <= mesage address
	450	li $5, 10 # $5 <= message length
	451	jal _tty_write # print BAR value
	452
	453	j _exit # end program
	454
	455	# Exceptions Messages table (indexed by CAUSE)
	456	mess_causes:
	457	.word msg_ukncause
	458	.word msg_ukncause
	459	.word msg_ukncause
	460	.word msg_ukncause
	461	.word msg_adel
	462	.word msg_ades
	463	.word msg_ibe
	464	.word msg_dbe
	465	.word msg_ukncause
	466	.word msg_bp
	467	.word msg_ri
	468	.word msg_cpu
	469	.word msg_ovf
	470	.word msg_ukncause
	471	.word msg_ukncause
	472	.word msg_ukncause
	473
	474	/*****************************************************************
	475	* All messages
	476	* Messages length are fixed : 8 or 36 characters...
	477	*****************************************************************/
	478	msg_bar: .asciiz "\nBAR = "
	479	msg_epc: .asciiz "\nEPC = "
	480	msg_default: .asciiz "\n\n !!! Default ISR !!! \n"
	481	msg_uknsyscall: .asciiz "\n\n !!! Undefined System Call !!! \n"
	482	msg_ukncause: .asciiz "\n\nException : strange unknown cause\n"
	483	msg_adel: .asciiz "\n\nException : illegal read address \n"
	484	msg_ades: .asciiz "\n\nException : illegal write address\n"
	485	msg_ibe: .asciiz "\n\nException : inst bus error \n"
	486	msg_dbe: .asciiz "\n\nException : data bus error \n"
	487	msg_bp: .asciiz "\n\nException : breakpoint \n"
	488	msg_ri: .asciiz "\n\nException : reserved instruction \n"
	489	msg_ovf: .asciiz "\n\nException : arithmetic overflow \n"
	490	msg_cpu: .asciiz "\n\nException : illegal coproc access\n"
	491	.align 2
	492
	493
	494	/***************************************************************************
	495	* _ctx_switch
	496	* The _ctx_switch function performs a context switch between the
	497	* current task and another task.
	498	* It can be used in a multi-processor architecture, with the assumption
	499	* that the tasks are statically allocated to processors.
	500	* The max number of processorsi is 8, and the max number of tasks is 4.
	501	* The scheduling policy is very simple : For each processor, the task index
	502	* is incremented, modulo the number of tasks allocated to the processor.
	503	*
	504	* It has no argument, and no return value.
	505	*
	506	* It uses three global variables:
	507	* - _current_task_array : an array of 8 task index:
	508	* (index of the task actually running on each processor)
	509	* - _task_number_array : an array of 8 numbers:
	510	* (the number of tasks allocated to each processor)
	511	* - _task_context_array : an array of 32 task contexts:
	512	* (at most 8 processors / each processor can run up to 4 tasks)
	513	* A task context is an array of 64 words = 256 bytes.
	514	* It is indexed by m = (proc_id*4 + task_id)
	515	* It contains copies of the processor registers.
	516	* As much as possible a register is stored at the index defined by its number
	517	* ( for example, $8 is saved in ctx[8]).
	518	* The exception are :
	519	* $0 is not saved since always 0
	520	* $26, $27 are not saved since not used by the task
	521	*
	522	* 04(ctx) SR 84(ctx) $8 164(ctx) $16 244(ctx) $24 32*4(ctx) EPC
	523	* 14(ctx) $1 94(ctx) $9 174(ctx) $17 254(ctx) $25 33*4(ctx) CR
	524	* 24(ctx) $2 104(ctx) $10 184(ctx) $18 264(ctx) LO 34*4(ctx) reserved
	525	* 34(ctx) $3 114(ctx) $11 194(ctx) $19 274(ctx) HI 35*4(ctx) reserved
	526	* 44(ctx) $4 124(ctx) $12 204(ctx) $20 284(ctx) $28 36*4(ctx) reserved
	527	* 54(ctx) $5 134(ctx) $13 214(ctx) $21 294(ctx) $29 37*4(ctx) reserved
	528	* 64(ctx) $6 144(ctx) $14 224(ctx) $22 304(ctx) $30 38*4(ctx) reserved
	529	* 74(ctx) $7 154(ctx) $15 234(ctx) $23 314(ctx) $31 39*4(ctx) reserved
	530	*
	531	* The return address contained in $31 is saved in the _current task context
	532	* (in the ctx[31] slot), and the function actually returns to the address contained
	533	* in the ctx[31] slot of the new task context.
	534	*
	535	* Caution : This function is intended to be used with periodic interrupts.
	536	* It can be directly called by the OS, but interrupts must be disabled before calling.
	537	***************************************************************************************/
	538
	539	.section .ksave
	540
	541	.global _task_context_array # initialised in reset.s
	542	.global _current_task_array # initialised in reset.s
	543	.global _task_number_array # initialised in reset.s
	544
	545	_task_context_array: # 32 contexts : indexed by (proc_id*4 + task_id)
	546	.space 8192
	547
	548	_current_task_array: # 8 words : indexed by the proc_id
	549	.word 0 # _current_task_array[0] <= 0
	550	.word 0 # _current_task_array[1] <= 0
	551	.word 0 # _current_task_array[2] <= 0
	552	.word 0 # _current_task_array[3] <= 0
	553	.word 0 # _current_task_array[4] <= 0
	554	.word 0 # _current_task_array[5] <= 0
	555	.word 0 # _current_task_array[6] <= 0
	556	.word 0 # _current_task_array[7] <= 0
	557
	558	_task_number_array: # 8 words : indexed by the proc_id
	559	.word 1 # _task_number_array[0] <= 1
	560	.word 1 # _task_number_array[1] <= 1
	561	.word 1 # _task_number_array[2] <= 1
	562	.word 1 # _task_number_array[3] <= 1
	563	.word 1 # _task_number_array[4] <= 1
	564	.word 1 # _task_number_array[5] <= 1
	565	.word 1 # _task_number_array[6] <= 1
	566	.word 1 # _task_number_array[7] <= 1
	567
	568	/***************************************************************************************/
	569
	570	.section .switch
	571
	572	.global _ctx_switch # makes it an external symbol
	573	.align 2
	574
	575	_ctx_switch:
	576
	577	# test if more than one task on the processor
	578
	579	mfc0 $26, $15, 1
	580	andi $26, $26, 0x7 # $26 <= proc_id
	581	sll $26, $26, 2 # $26 <= 4*proc_id
	582	la $27, _task_number_array # $27 <= base address of _task_number_array
	583	addu $27, $27, $26 # $27 <= _task_number_array + 4*proc_id
	584	lw $27, ($27) # $27 <= task number
	585	addi $26, $27, -1 # $26 <= _task_number - 1
	586	bnez $26, do_it # 0 if only one task
	587	jr $31 # return
	588
	589	# save _current task context
	590
	591	do_it:
	592	mfc0 $26, $15, 1
	593	andi $26, $26, 0x7 # $26 <= proc_id
	594	sll $26, $26, 2 # $26 <= 4*proc_id
	595	la $27, _current_task_array # $27 <= base address of _current_task_array
	596	addu $27, $27, $26 # $27 <= _current_task_array + 4*proc_id
	597	lw $26, ($27) # $26 <= current task index
	598	sll $26, $26, 8 # $26 <= 256*task_id
	599	la $27, _task_context_array # $27 <= base address of context array
	600	addu $27, $27, $26 # $27 <= _task_context_array + 256*task_id
	601	mfc0 $26, $15, 1
	602	andi $26, $26, 0x7 # $26 <= proc_id
	603	sll $26, $26, 10 # $26 <= 1024*proc_id
	604	addu $27, $27, $26 # $27 <= taxk_context_array + 256(proc_id4 + task_id)
	605
	606	mfc0 $26, $12 # $26 <= SR
	607	sw $26, 0*4($27) # ctx[0] <= SR
	608	.set noat
	609	sw $1, 1*4($27) # ctx[1] <= $1
	610	.set at
	611	sw $2, 2*4($27) # ctx[2] <= $2
	612	sw $3, 3*4($27) # ctx[3] <= $3
	613	sw $4, 4*4($27) # ctx[4] <= $4
	614	sw $5, 5*4($27) # ctx[5] <= $5
	615	sw $6, 6*4($27) # ctx[6] <= $6
	616	sw $7, 7*4($27) # ctx[7] <= $7
	617	sw $8, 8*4($27) # ctx[8] <= $8
	618	sw $9, 9*4($27) # ctx[9] <= $9
	619	sw $10, 10*4($27) # ctx[10] <= $10
	620	sw $11, 11*4($27) # ctx[11] <= $11
	621	sw $12, 12*4($27) # ctx[12] <= $12
	622	sw $13, 13*4($27) # ctx[13] <= $13
	623	sw $14, 14*4($27) # ctx[14] <= $14
	624	sw $15, 15*4($27) # ctx[15] <= $15
	625	sw $16, 16*4($27) # ctx[16] <= $16
	626	sw $17, 17*4($27) # ctx[17] <= $17
	627	sw $18, 18*4($27) # ctx[18] <= $18
	628	sw $19, 19*4($27) # ctx[19] <= $19
	629	sw $20, 20*4($27) # ctx[20] <= $20
	630	sw $21, 21*4($27) # ctx[21] <= $21
	631	sw $22, 22*4($27) # ctx[22] <= $22
	632	sw $23, 23*4($27) # ctx[23] <= $23
	633	sw $24, 24*4($27) # ctx[24] <= $24
	634	sw $25, 25*4($27) # ctx[25] <= $25
	635	mflo $26
	636	sw $26, 26*4($27) # ctx[26] <= LO
	637	mfhi $26
	638	sw $26, 27*4($27) # ctx[27] <= H1
	639	sw $28, 28*4($27) # ctx[28] <= $28
	640	sw $29, 29*4($27) # ctx[29] <= $29
	641	sw $30, 30*4($27) # ctx[30] <= $30
	642	sw $31, 31*4($27) # ctx[31] <= $31
	643	mfc0 $26, $14
	644	sw $26, 32*4($27) # ctx[32] <= EPC
	645	mfc0 $26, $13
	646	sw $26, 33*4($27) # ctx[33] <= CR
	647
	648	# select the new task
	649
	650	mfc0 $15, $15, 1
	651	andi $15, $15, 0x7 # $15 <= proc_id
	652	sll $16, $15, 2 # $16 <= 4*proc_id
	653	la $17, _current_task_array # $17 <= base address of _current_task_array
	654	addu $17, $17, $16 # $17 <= _current_task_array + 4*proc_id
	655	lw $18, ($17) # $18 <= _current task index
	656	la $19, _task_number_array # $19 <= base address of _task_number_array
	657	addu $19, $19, $16 # $19 <= _task_number_array + 4*proc_id
	658	lw $20, ($19) # $20 <= max = number of tasks
	659	addiu $18, $18, 1 # $18 <= new task index
	660	sub $2, $18, $20 # test modulo max
	661	bne $2, $0, no_wrap
	662	add $18, $0, $0 # $18 <= new task index
	663	no_wrap:
	664	sw $18, ($17) # update _current_task_array
	665
	666	# restore next task context
	667
	668	sll $19, $18, 8 # $19 <= 256*task_id
	669	la $27, _task_context_array # $27 <= base address of context array
	670	addu $27, $27, $19 # $27 <= _task_context_array + 256*task_id
	671	sll $19, $15, 10 # $19 <= 1024*proc_id
	672	addu $27, $27, $19 # $27 <= _task_context_array + 256(proc_id4 + task_id)
	673
	674	lw $26, 0*4($27)
	675	mtc0 $26, $12 # restore SR
	676	.set noat
	677	lw $1, 1*4($27) # restore $1
	678	.set at
	679	lw $2, 2*4($27) # restore $2
	680	lw $3, 3*4($27) # restore $3
	681	lw $4, 4*4($27) # restore $4
	682	lw $5, 5*4($27) # restore $5
	683	lw $6, 6*4($27) # restore $6
	684	lw $7, 7*4($27) # restore $7
	685	lw $8, 8*4($27) # restore $8
	686	lw $9, 9*4($27) # restore $9
	687	lw $10, 10*4($27) # restore $10
	688	lw $11, 11*4($27) # restore $11
	689	lw $12, 12*4($27) # restore $12
	690	lw $13, 13*4($27) # restore $13
	691	lw $14, 14*4($27) # restore $14
	692	lw $15, 15*4($27) # restore $15
	693	lw $16, 16*4($27) # restore $16
	694	lw $17, 17*4($27) # restore $17
	695	lw $18, 18*4($27) # restore $18
	696	lw $19, 19*4($27) # restore $19
	697	lw $20, 20*4($27) # restore $20
	698	lw $21, 21*4($27) # restore $21
	699	lw $22, 22*4($27) # restore $22
	700	lw $23, 23*4($27) # restore $23
	701	lw $24, 24*4($27) # restore $24
	702	lw $25, 25*4($27) # restore $25
	703	lw $26, 26*4($27)
	704	mtlo $26 # restore LO
	705	lw $26, 27*4($27)
	706	mthi $26 # restore HI
	707	lw $28, 28*4($27) # restore $28
	708	lw $29, 29*4($27) # restore $29
	709	lw $30, 30*4($27) # restore $30
	710	lw $31, 31*4($27) # restore $31
	711	lw $26, 32*4($27)
	712	mtc0 $26, $14 # restore EPC
	713	lw $26, 33*4($27)
	714	mtc0 $26, $13 # restore CR
	715
	716	jr $31 # returns to caller
	717
	718	/* Local Variables:
	719	tab-width: 4;
	720	c-basic-offset: 4;
	721	c-file-offsets:((innamespace . 0)(inline-open . 0));
	722	indent-tabs-mode: nil;
	723	End: */
	724
	725	/* vim: set filetype=asm expandtab shiftwidth=4 tabstop=4 softtabstop=4: */
	726

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