From eec40b069ad6cf8e91c358bf37b5518e4b0623ff Mon Sep 17 00:00:00 2001
From: taitep <taitep@taitep.se>
Date: Sun, 21 Dec 2025 14:24:20 +0100
Subject: [PATCH] Implement SB

---
 src/instructions.rs     |  1 +
 src/instructions/rvi.rs | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/src/instructions.rs b/src/instructions.rs
index fc270dc..5261dde 100644
--- a/src/instructions.rs
+++ b/src/instructions.rs
@@ -30,6 +30,7 @@ pub(crate) fn find_and_exec(instr: Instruction, core: &mut Core) -> Option<Instr
         },
         0b01000 => match instr.funct3() {
             // STORE
+            0b000 => Some(rvi::sb(core, instr)),
             0b011 => Some(rvi::sd(core, instr)),
             _ => None,
         },
diff --git a/src/instructions/rvi.rs b/src/instructions/rvi.rs
index 1fe1c7a..89d142b 100644
--- a/src/instructions/rvi.rs
+++ b/src/instructions/rvi.rs
@@ -53,6 +53,22 @@ pub fn sd(core: &mut Core, instr: Instruction) -> InstructionResult {
     }
 }
 
+pub fn sb(core: &mut Core, instr: Instruction) -> InstructionResult {
+    let addr = core.reg_read(instr.rs1()).wrapping_add(instr.imm_s());
+
+    let page = (addr / 4096) as PageNum;
+    let offset = (addr & (4096 as Addr - 1)) as u16;
+    let value = core.reg_read(instr.rs2()) as u8;
+
+    match core.mem.write_byte(page, offset, value) {
+        Ok(_) => {
+            core.pc = core.pc.wrapping_add(4);
+            InstructionResult::Normal
+        }
+        Err(_) => InstructionResult::Exception(()),
+    }
+}
+
 pub fn lui(core: &mut Core, instr: Instruction) -> InstructionResult {
     core.reg_write(instr.rd(), instr.imm_u());
     core.pc = core.pc.wrapping_add(4);