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Proposed patch for issue #29 (related to RCM4110 Rev F hardware) #30

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Proposed patch for issue #29 (related to RCM4110 Rev F hardware) #30

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3fd046f
bios: don't disable early /OE in MTCR
tomlogic Mar 10, 2021
11168a7
bios: enable early /OE for RCM4110
tomlogic Mar 10, 2021
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2 changes: 0 additions & 2 deletions Lib/Rabbit4000/BIOSLIB/CPUPARAM.LIB
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Original file line number Diff line number Diff line change
Expand Up @@ -122,8 +122,6 @@ _enableClockModulation::
bool hl
#if ENABLE_SPREADER == 0 // spreader disabled
xor a
ld (MTCRShadow), a
ioi ld (MTCR), a // normal /OE0 and /OE1 timing
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@tomlogic tomlogic Apr 6, 2021

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Even with the spreader disabled, we should keep the "early /OE" setting on products that have enabled it.

ld (GCM0RShadow), a
ioi ld (GCM0R), a
ld (GCM1RShadow), a
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12 changes: 10 additions & 2 deletions Lib/Rabbit4000/BIOSLIB/StdBios.c
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Expand Up @@ -1874,6 +1874,13 @@ ioi ld (STACKSEG), a
#endif
//end serial flash fast RAM copy

#if _BOARD_TYPE_ == RCM4110
; RCM4110 with 55ns flash requires early output enable on MTCR when running
; with 0 wait states, so configure that before setting MB0CR.
ld a, 0x0C
ioi ld (MTCR), a
#endif

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@tomlogic tomlogic Apr 6, 2021

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This change enables "early /OE" on the RCM4110 before reaching code that configures MB0CR for 0 wait states, and therefore will access the RCM4110's 55ns flash at full speed.

.fastRAMCopyDone::
; Following a fast RAM copy, the current device mapped to MB0 and the device
; that is actually supposed to be mapped to MB0 contain the same code at this
Expand Down Expand Up @@ -2613,14 +2620,15 @@ _more_inits0::
// Initialize the status pin, clocks, clock doubler, debug baud rate
_more_inits02::
lcall _getDoublerSetting ; get doubler setting value into L (h always 0)
ld a, L ; zero value also disables /OEx early output
ld a, L
or a ; update the Zero flag
jr z, .notEarlyOutputEnable

ld a, 0x0C ; value to set both /OE0 and /OE1 early output
.notEarlyOutputEnable:
ioi ld (MTCR), a ; first, update /OE0, /OE1 early output enable
ld (MTCRShadow), a

.notEarlyOutputEnable:
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@tomlogic tomlogic Apr 6, 2021

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This change leaves MTCR unmodified when the clock doubler isn't enabled -- allowing the RCM4110 setting from line 1881 to remain in place.

ld a, L ; recover the doubler setting value
ioi ld (GCDR), a ; next, update clock doubler setting
ld (GCDRShadow), a
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