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Enable early /OE in more configurations #8

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Enable early /OE in more configurations #8

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eabee26
BIOS: don't modify MTCR if spectrum spreading disabled
tomlogic Mar 25, 2021
b529bc8
BIOS: enable early /OE before clock doubler
tomlogic Apr 6, 2021
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9 changes: 1 addition & 8 deletions Lib/BIOSLIB/CPUPARAM.LIB
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Original file line number Diff line number Diff line change
Expand Up @@ -162,14 +162,7 @@ END DESCRIPTION ***************************************************************/
#asm xmem nodebug
_enableClockModulation::
bool hl
#if _CPU_ID_ < R2000_R3
ld l, h
lret
#elif ENABLE_SPREADER == 0 // spreader disabled
xor a
ld (MTCRShadow), a
; ioi ld (MTCR), a // normal /OE0 and /OE1 timing
IOWRITE_A(MTCR)
#if _CPU_ID_ < R2000_R3 || ENABLE_SPREADER == 0
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This change ensures that we don't disable "early /OE" if it was previously enabled. Startup default is disabled (0x00), but the StdBios.c change around line 2455 will automatically enable it on all products with a doubled clock, and later code in this function enables it before turning on the spectrum spreader.

ld l, h
lret
#else
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17 changes: 12 additions & 5 deletions Lib/BIOSLIB/StdBios.c
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Expand Up @@ -2452,12 +2452,19 @@ _more_inits02::
ld hl, GCSRShadow
ld (hl), a

lcall _getDoublerSetting

ld a, l
lcall _getDoublerSetting ; get doubler setting value into L (h always 0)
ld a, L
or a ; update the Zero flag
jr z, .notDoubled

ld a, 0x0C ; value to set both /OE0 and /OE1 early output
ioi ld (MTCR), a ; first, update /OE0, /OE1 early output enable
ld (MTCRShadow), a
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This change, backported from Dynamic C PR 30, enables "early /OE" before enabling the clock doubler.

Note that Dynamic C 9 could use the existing code from that sets MTCR and its shadow to 0 if the clock doubler is disabled, since there isn't any code earlier in the BIOS attempting to set it (as the Dynamic C 10 patch does for the RCM4110).


.notDoubled:
ld a, L ; recover the doubler setting value
ioi ld (GCDR), a ; next, update clock doubler setting
ld (GCDRShadow), a
ioi ld (GCDR), a ; set clock doubler now


#if _CPU_ID_ >= R2000_R3
lcall _enableClockModulation ; enables spreader
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