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nexus: reduce OSCA worst case to 7%

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The current version of Crosslink-NX Family Data Sheet lists the high
frequency oscillator maximum frequency as 481.5MHz (that is, 7% higher
than its nominal 450MHz):

https://www.latticesemi.com/-/media/LatticeSemi/Documents/DataSheets/CrossLink/FPGA-DS-02049-1-2-1-CrossLink-NX-Family.ashx?document_id=52780

Older documents listed a wider frequency range but ±7% is the range for
production parts.
This commit is contained in:
Dan Callaghan 2022-02-10 15:48:06 +11:00
parent 74c99f9195
commit 5c30093360
1 changed files with 1 additions and 1 deletions
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2
nexus/pack.cc
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@ -1987,7 +1987,7 @@ struct NexusPacker
copy_constraint(ci, id_CLKI, id_CLKO, 1);
} else if (ci->type == id_OSC_CORE) {
int div = int_or_default(ci->params, ctx->id("HF_CLK_DIV"), 128);
const float tol = 1.15f; // OSCA has +/-15% frequency tolerance, assume the worst case.
const float tol = 1.07f; // OSCA has +/-7% frequency tolerance, assume the worst case.
set_period(ci, id_HFCLKOUT, delay_t((1.0e6 / 450) * (div + 1) / tol));
set_period(ci, id_LFCLKOUT, delay_t((1.0e3 / 10) / tol));
} else if (ci->type == id_PLL_CORE) {