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There may be instances where we want a non-zero MTCR even if the spectrum spreader is disabled. By leaving it unmodified, it might still be zero from the default startup value, or set non-zero elsewhere.
This increases the /OE timing margin for 29MHz products with 55ns flash memory for the brief moment before _enableClockModulation() enables it, and ensures it's still enabled if the spectrum spreader is disabled.
tomlogic
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Apr 6, 2021
| 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.
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| 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).
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This branch addresses issue #7 affecting updated 29MHz products using 55ns flash memory, and will become part of the master branch once approved for release.