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/*
* Creation Date: <2001/06/21 17:10:35 samuel>
* Time-stamp: <2001/06/24 00:25:37 samuel>
*
* <dec.S>
*
* DEC / TimeBase stuff
*
* Copyright (C) 2001 Samuel Rydh (samuel@ibrium.se)
*
* This program 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
*
*/
/************************************************************************/
/* TBWU / TBWL */
/************************************************************************/
#if 0
spr_tbwu:
blr // read (won't come here)
mr r3,r0
mftb r4
b update_tb
spr_tbwl:
blr // read (won't come here)
mftbu r3
mr r4,r0
// ...fall through...
// r3 = tbu, r4 = tbl, r0,r2,r5 free.
update_tb:
lwz r5,K_LOADED_DEC(r1)
mfdec r2
sub r5,r5,r2 // r5 = elapsed ticks
li r2,0 // Set timebase
mttbl r4
mttbu r3
mttbl r4
mfxer r2
subfc r4,r5,r4
addme r3,r3
stw r4,xTBL(r1)
stw r3,xTBU(r1)
mtxer r2
b emulation_done
#endif
/************************************************************************/
/* Load/restore DEC and TB */
/************************************************************************/
//////////////////////////////////////////////////////////////
// recalc_int_stamp
//
// May modify: r0,r2-r5
//
recalc_int_stamp:
crclr FBIT_RecalcDecInt
lwz r5,xTIMER_STAMP(r1)
bf FBIT_DecSeenZero, 2f // FBIT_DecSeenZero must be set when DEC is loaded
mftb r3
lwz r4,xDEC_STAMP(r1) // Has the xDEC overflown already?
sub. r0,r4,r3
blt 3f
sub. r0,r4,r5
bge 2f // branch if xDEC > xTIMER
mr r5,r4
2: stw r5,K_INT_STAMP(r1) // dec = xTIMER
blr
// We should consider a fb-bit to throw an exceptions direcltly instead.
// All exceptions could be handled that way.
3: stw r4,K_INT_STAMP(r1) // dec = 0
blr
//////////////////////////////////////////////////////////////
// set_mol_dec
//
// May modify: r0,r2-r5
//
// Old 2.4 kernels assume that linux-DEC never ticks faster
// than the DEC interval measured from TB. Unfortunately,
// it is virtually impossible to keep DEC/TB in sync.
//
// Experimentally, the "worst case" senario is a linux DEC tick
// beeing delayed 0.04 ms (to be compare with the 20 ms period).
//
// Sequences similar to
//
// 1: mftb r2; mfdec r3; mftb r4; cmp r2,r4; bne 1b
//
// do *not* work - DEC and TB probably ticks on different edges.
set_mol_dec:
lwz r5,K_INT_STAMP(r1) // DEC = K_INT_STAMP - tbl
mfdec r3 // Make sure linux interrupt *never*
mftb r2 // occur too fast
sub r4,r5,r2
cmpw r4,r3
bgtlr
add r5,r3,r2 // K_DEC_STAMP = DEC + tbl
mtdec r4
stw r5,K_DEC_STAMP(r1)
crset FBIT_MolDecLoaded
blr
///////////////////////////////////////////////////////////////
// set_kernel_dec
//
// May modify: r0,r2, cr
//
set_kernel_dec:
lwz r0,K_DEC_STAMP(r1)
crclr FBIT_MolDecLoaded
mftb r2 // Keep linux-DEC coherent
sub r2,r0,r2 // DEC = stamp - tbl
mtdec r2
blr
/************************************************************************/
/* DEC read/write */
/************************************************************************/
spr_dec:
b _dec_read
// dec write. r0 = spr_value
// r2=sprn# (used after a blr)
rlwinm. r5,r0,0,0,0 // seen zero?
mftb r4
cror FBIT_DecSeenZero,FBIT_DecSeenZero,eq
add r5,r4,r0
stw r5,xDEC_STAMP(r1) // set new dec value
bf FBIT_DecSeenZero, emulation_done
bl recalc_int_stamp // M: r0,r2-r5
btl FBIT_MolDecLoaded, set_kernel_dec // M: r0,r2
bl set_mol_dec // M: r0,r2-r5
b emulation_done
// r0 = ret value, r3,r4 = scratch
_dec_read:
lwz r4,xDEC_STAMP(r1)
mftb r3
sub r0,r4,r3
blr
/************************************************************************/
/* Decrementer Exception */
/************************************************************************/
// __dec_VECTOR (non-MOL dec exception)
//
// r3=cr, sprg1=saved_r1, sprg0=saved_r3
//
// An exception with DEC>=0 can occur if a mac-DEC overflows occurs
// just prior to a context switch. These exceptions should be
// dropped silently.
__dec_VECTOR:
mfdec r1
cmpwi r1,0
blt+ 1f
mtcr r3 // Restore and exit
mfsprg1 r1
mfsprg0 r3
rfi
1:
mtcr r3 // Restore and continue trap
mfsprg1 r1
mfsprg0 r3
b continue_trap_0x900
VECTOR_( 0x900, "Decrementer", secint_bad, __dec_VECTOR )
EXCEPTION_PREAMBLE // r0-r5, CR, LR
TRACE(0x900, "Decrementer")
mfdec r4
cmpwi r4,0
bge exception_return
bl save_middle_regs // We *will* take an exception
bf FBIT_MolDecLoaded, take_linux_dec_exception
lis r8,0x1000 // DEC rearm constant
mftb r3
bf FBIT_DecSeenZero, 1f // check for xDEC overflow
lwz r4,xDEC_STAMP(r1)
sub. r6,r4,r3
bge 1f
crset FBIT_DecINT
crclr FBIT_DecSeenZero
1:
lwz r5,xTIMER_STAMP(r1) // check for xTIMER overflow
sub. r5,r5,r3
bge 2f
crset FBIT_TimerINT
2:
crset FBIT_RecalcDecInt
crset FBIT_CheckFlags
mtdec r8 // rearm DEC
MAC_EXIT( RVEC_INTERRUPT ) // XXX: Something else?
take_linux_dec_exception:
TAKE_EXCEPTION
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