eater: update docs

1 files changed, 68 insertions, 25 deletions

diff --git a/eater_cpu/readme.txt b/eater_cpu/readme.txt
index 51a63b2..f92fdd7 100644
--- a/eater_cpu/readme.txt
+++ b/eater_cpu/readme.txt
@@ -1,25 +1,68 @@
-                  |   4 LSB      
-                  +<--------> PC 
-                  |              
-                  |              
-       4 LSB      |              
-MAR  <------------+<--------> A  
- |                |           |  
- | 4 LSB          |           |  
- |                |           |  
- v                |           v  
-RAM <------------>|<-------- ALU 
-                  |           ^  
-                  |           |  
-                  |           |  
-                  |           |  
-    <-------------+           |  
- IR ------------->|<--------> B  
- |    4 LSB       |              
- |                |              
- |                |              
- | 4 MSB          +---------> OUT
- |                |            | 
- v                |            | 
- ins                           v 
- decoder                   DISPLAY
+                       4 LSB      
+                   +<--------> PC 
+                   |              
+                   |              
+        4 LSB      |              
+ MAR <-------------+<--------> A  
+  |                |           |  
+  | 4 LSB          |           |  
+  |                |           |  
+  v                |           v  
+ RAM <------------>|<-------- ALU 
+                   |           ^  
+                   |           |  
+                   |           |  
+                   |           |  
+     <-------------+           |  
+  IR ------------->|<--------> B  
+  |    4 LSB       |              
+  |                |              
+  |                |              
+  | 4 MSB          +---------> OUT
+  |                             | 
+  v                             | 
+  ins                           v 
+  decoder                   DISPLAY
+
+---
+
+instruction set
+
+LDA <memaddress>  0b_0000_<memaddress>    Load memory > A
+ADD <memaddress>  0b_0001_<memaddress>    "Add memory" + A -> A
+OUT <memaddress>  0b_1110_xxxx            Output A -> OUT
+
+---
+
+operation
+
+1. Load instruction @ PC into INS,
+   Increment PC.
+   a) PC out -> MAR
+   (PC_to_bus) + (bus_to_MAR) + (clk)
+   b) MEM -> INS
+   (RAM_to_bus) + (bus_to_INS) + (clk)
+   c) PC++
+   (PC_count_en) + (clk)
+
+2. Decode and execute instruction.
+
+2.I LDA: Load memory into A
+   a) INS_lsb -> MAR
+   (INS_to_bus) + (bus_to_MAR) + (clk)
+   b) MEM -> A
+   (RAM_to_bus) + (bus_to_A) + (clk)
+
+2.II ADD: Load mem in B,
+   ALU "auto" adds,
+   put back in A
+   a) INS_lsb -> MAR
+   (INS_to_bus) + (bus_to_MAR) + (clk)
+   b) MEM -> B
+   (RAM_to_bus) + (bus_to_B) + (clk)
+   c) ALU -> A
+   (ALU_to_bus) + (bus_to_A) + (clk)
+
+2.III OUT: Put A in OUT
+   a) A -> OUT
+   (A_to_bus) + (bus_to_OUT) + (clk)