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authorRob Austein <sra@hactrn.net>2015-09-27 13:17:55 -0400
committerRob Austein <sra@hactrn.net>2015-09-27 13:17:55 -0400
commitcf8167215459811f8047f7c6d4f5972d924f6689 (patch)
tree2a6652039b18c15b9d8b4476f4b32b3640db8713 /config
parent19e4044fcf47360dcc5aa68f6eae5a62a6cdb61b (diff)
Comments noting the strange history of the addressing scheme.
Diffstat (limited to 'config')
-rwxr-xr-xconfig/config.py38
1 files changed, 38 insertions, 0 deletions
diff --git a/config/config.py b/config/config.py
index 970b339..4648f9d 100755
--- a/config/config.py
+++ b/config/config.py
@@ -3,6 +3,44 @@
Generate core_selector.v for a set of cores.
"""
+# History of cryptech bus addressing scheme, as best I understand it.
+#
+# The old old addressing scheme that Joachim and Paul came up with
+# was:
+#
+# 3 bits of segment selector [16:14]
+# 6 bits of core selector [13:8]
+# 8 bits of register selector [7:0]
+#
+# modexp6s needed more register bits than that, so Pavel changed
+# addressing within the math segment to:
+#
+# 3 bits of segment selector [16:14]
+# 4 bits of core selector [13:10]
+# 10 bits of register selector [9:0]
+#
+# Meanwhile, Paul eliminated segments entirely when writing the
+# ancestor of this script, resulting in:
+#
+# 9 bits of core selector [16:8]
+# 8 bits of register selector [7:0]
+#
+# Taking Pavel's and Paul's changes together, we want:
+#
+# 7 bits of core selector [16:10]
+# 10 bits of register selector [9:0]
+#
+# Open issue: what effect does all this have on the sub-core muxing
+# within trng cores? trng core plus its (currently) four sub-cores
+# still takes up more than one new core slot even if trng uses the old
+# scheme internally. How many slots should we allocate, and what
+# addressing scheme is the trng core expecting to see?
+
+# Unrelated: Timing delays. Paul added extra registers to slow cores
+# other than modexps6 down by one clock cycle, to compensate for the
+# one cycle delay that seems to be built into the block memories that
+# modexps6 uses. Templates will need to reflect that somehow.
+
def main():
"""
Parse arguments and config file, generate core list, generate output.