From 82cc71261d3d32012d33d3bebe56ca5e3b0bcdbd Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sun, 2 Oct 2022 15:32:49 -0700
Subject: Initial commit.

---
 BigGolf | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 135 insertions(+)
 create mode 100644 BigGolf

(limited to 'BigGolf')

diff --git a/BigGolf b/BigGolf
new file mode 100644
index 0000000..9a308bd
--- /dev/null
+++ b/BigGolf
@@ -0,0 +1,135 @@
+The "Big Golf" Microarchitecture
+
+
+
+Allowed memory combinations:
+  * Any two loads
+  * Any two stores with different addresses (n.b. LLC is limited to 1 eviction per cycle)
+  * Any load with any younger store
+
+Instruction opcodes:
+  0 AND logical AND from memory to accumulator
+  1 TAD Two's-complement ADd from memory to accumulator
+  2 ISZ Increment and Skip if Zero
+  3 DCA Deposit and Clear Accumulator
+  4 JMS JuMp Subroutine
+  5 JMP JuMP
+  6 IOT In-Out Transfer (device accesses)
+  7 OPR microsequenced OPeRations (miscellaneous, like clear/rotate/etc)
+
+Memory transactions:       Opcodes that do it: (second set is the indirect versions)
+  * Fetch instruction        01234567 01234567
+  * Indirect address load             0123
+  * Autoincrement store               0123
+  * Execution load           012      012 45
+  * Execution store            234      234
+
+
+
+┌─────┐       ┌──────┐                ┌────┐
+│Fetch├──────►│Decode│              ┌►│Exec│
+└─────┘       └──────┘              │ └────┘
+                                    │
+ next_pc    ┌──init_indirect_load   │  init_execution_store
+            │  init_execution_load──┤  retire
+            │  init_execution_store │
+            │  retire               │
+            │  rubberband_stall(1/2)│
+            │                       │
+            │ ┌───────┐             │
+            └►│Autoinc│             │
+              └───────┘             │
+                                    │
+            ┌──init_autoinc_store   │
+            │  init_execution_load──┤
+            │  init_execution_store │
+            │  retire               │
+            │                       │
+            │ ┌─────┐               │
+            └►│Indir│               │
+              └─────┘               │
+                                    │
+               init_execution_load──┘
+               init_execution_store
+               retire
+
+
+
+Possible arbitration techniques:
+  * Rubberband stalling in Decode + positional arbitration
+  * Age/address/operation comparison without rubberbanding
+    * Longer clock cycles, or
+    * Extra cycle
+
+What to do with cache misses?
+  * Stall entire pipeline to maintain simpler ordering constraints
+  * If only loads are missing, allow everything else to proceed?
+  * Always allow Fetch to proceed?
+
+Need separate logic to detect SMC clobbers *anyway*
+
+
+
+OPR opcodes:
+
+    "group 1"
+         _0___1___2_ _3_ _4_ _5_ _6_ _7_ _8_ _9_ _10 _11
+        |           |   |   |   |   |   |RAR|RAL| 0 |   |
+        | 1   1   1 | 0 |CLA|CLL|CMA|CML|RTR|RTL| 1 |IAC|
+        |___|___|___|___|___|___|___|___|___|___|___|___|
+
+        CLA CLear Accumulator
+        CLL CLear Link
+        CMA CoMplement Accumulator
+        CML CoMplement Link
+        RAR Rotate Accumulator Right (if bit 10 is 0)
+        RAL Rotate Accumulator Left (if bit 10 is 0)
+        RTR Rotate (Twice) accumulator and link Right (if bit 10 is 1)
+        RTL Rotate (Twice) accumulator and link Left (if bit 10 is 1)
+        IAC Increment ACcumulator
+        BSW Byte Swap word in accumulator (if bits 8 and 9 are 0, and bit 10 is 1)
+
+        Logical order of operations:
+            CLA, CLL
+            CMA, CML
+            IAC
+            RAR, RAL, RTR, RTL, BSW
+
+    "group 2"
+         _0___1___2_ _3_ _4_ _5_ _6_ _7_ _8_ _9_ _10 _11
+        |           |   |   |SMA|SZA|SNL| 0 |   |   |   |
+        | 1   1   1 | 1 |CLA|SPA|SNA|SZL| 1 |OSR|HLT| 0 |
+        |___|___|___|___|___|___|___|___|___|___|___|___|
+
+        SMA Skip on Minus Accumulator (skip if high bit of accumulator is set) (if bit 8 is 0)
+        SPA Skip on Plus Accumulator (skip if high bit of accumulator is clear) (if bit 8 is 1)
+        SZA Skip on Zero Accumulator (if bit 8 is 0)
+        SNA Skip on Nonzero Accumulator (if bit 8 is 1)
+        SNL Skip on Nonzero Link (if bit 8 is 0)
+        SZL Skip on Zero Link (if bit 8 is 1)
+        OSR bitwise Or Switch Register into accumulator
+        HLT HaLT processor
+        CLA CLear Accumulator
+
+        Logical order of operations:
+            SMA, SZA, SNL
+            SPA, SNA, SZL
+            CLA
+            OSR, HLT
+
+    "mq"
+         _0___1___2_ _3_ _4_ _5_ _6_ _7_ _8_ _9_ _10 _11
+        |           |   |   |   |   |   |   |   |   |   |
+        | 1   1   1 | 1 |CLA|MQA|   |MQL|   |   |   | 1 |
+        |___|___|___|___|___|___|___|___|___|___|___|___|
+
+        CLA CLear Accumulator
+        MQL MQ Loads from Accumulator
+        MQA bitwise or MQ into Accumulator
+
+        bits 6,8,9,10 are used for extended arithmetic instructions
+        see https://homepage.divms.uiowa.edu/~jones/pdp8/refcard/74.html
+
+        Logical order of operations:
+            CLA
+            MQA, MQL (simultaneous parallel assignment)
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