From 63ca6b95b1f06f18ade4e58ba7ba42b09eeeb5d5 Mon Sep 17 00:00:00 2001
From: uvok
Date: Thu, 22 Jan 2026 19:43:31 +0100
Subject: Implement LDI

---
 eater_cpu/cpp/Veater_computer__main.cpp | 2 ++
 eater_cpu/eater_decoder.sv              | 8 ++++++++
 eater_cpu/eater_types.sv                | 4 ++++
 eater_cpu/readme.txt                    | 1 +
 4 files changed, 15 insertions(+)

diff --git a/eater_cpu/cpp/Veater_computer__main.cpp b/eater_cpu/cpp/Veater_computer__main.cpp
index fbfc978..4de8454 100644
--- a/eater_cpu/cpp/Veater_computer__main.cpp
+++ b/eater_cpu/cpp/Veater_computer__main.cpp
@@ -29,6 +29,8 @@ void load_program(const std::unique_ptr<Veater_computer> &topp) {
 
        // OUT
        0xe0,
+       // LDI 4
+       0x54,
        // NOP
        0x00,
        // HALT
diff --git a/eater_cpu/eater_decoder.sv b/eater_cpu/eater_decoder.sv
index fea00e0..20e3e0b 100644
--- a/eater_cpu/eater_decoder.sv
+++ b/eater_cpu/eater_decoder.sv
@@ -30,6 +30,7 @@ function CpuState insdep_state;
     ADD: insdep_state = ADD_INS_to_MAR;
     SUB: insdep_state = SUB_INS_to_MAR;
     STA: insdep_state = STA_INS_to_MAR;
+    LDI: insdep_state = LDI_INS_to_A;
     OUT: insdep_state = OUT_A_to_OUT;
     HALT_op: insdep_state = HALT_st;
 
@@ -65,6 +66,8 @@ always @(posedge clk_i) begin
     STA_INS_to_MAR: next_state = STA_A_to_MEM;
     STA_A_to_MEM: next_state = PC_to_MAR;
 
+    LDI_INS_to_A: next_state = PC_to_MAR;
+
     OUT_A_to_OUT: next_state = PC_to_MAR;
 
     HALT_st: next_state = HALT_st;
@@ -153,6 +156,11 @@ always_comb begin
         internal_flags.A_out = 1;
     end
 
+    LDI_INS_to_A: begin
+        internal_flags.INS_out = 1;
+        internal_flags.A_in = 1;
+    end
+
     OUT_A_to_OUT: begin
         internal_flags.A_out = 1;
         internal_flags.OUT_in = 1;
diff --git a/eater_cpu/eater_types.sv b/eater_cpu/eater_types.sv
index 6f69b4b..43e3a0d 100644
--- a/eater_cpu/eater_types.sv
+++ b/eater_cpu/eater_types.sv
@@ -44,6 +44,9 @@ typedef enum logic[7:0] {
     // STA: b) A -> MEM
     STA_A_to_MEM,
 
+    // LDI: a) LSB of INStruction into A
+    LDI_INS_to_A,
+
     // OUT: A -> OUT
     OUT_A_to_OUT,
 
@@ -57,6 +60,7 @@ typedef enum logic[3:0] {
     ADD = 'b0010,
     SUB = 'b0011,
     STA = 'b0100,
+    LDI = 'b0101,
     OUT = 'b1110,
     HALT_op = 'b1111
 } eater_instruction;
diff --git a/eater_cpu/readme.txt b/eater_cpu/readme.txt
index 402f0bb..57c65ef 100644
--- a/eater_cpu/readme.txt
+++ b/eater_cpu/readme.txt
@@ -33,6 +33,7 @@ LDA <memaddress>  0b_0001_<memaddress>    Load memory > A
 ADD <memaddress>  0b_0010_<memaddress>    "Add memory": mem>B, A + B -> A
 SUB <memaddress>  0b_0011_<memaddress>    "Sub memory": mem>B, A - B-> A
 STA <memaddress>  0b_0100_<memaddress>    Store A -> memory
+LDI <value>       0b_0101_<value>         Store <value> -> A
 OUT ____________  0b_1110_xxxx            Output A -> OUT
 HLT ____________  0b_1111_xxxx            Sets halt flag
 ---
-- 
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