From 4fa93e402d86a6d607ae0fdb1f2d2c4b7b2e3b67 Mon Sep 17 00:00:00 2001
From: Jordan Woyak <jordan.woyak@gmail.com>
Date: Fri, 20 Feb 2026 16:01:22 -0600
Subject: [PATCH] SI/SI_DeviceAMBaseboard: Expose the buffer size of 128 to
 eliminate some magic numbers.

---
 Source/Core/Core/HW/SI/SI.h                   |  4 +++-
 .../Core/Core/HW/SI/SI_DeviceAMBaseboard.cpp  | 23 +++++++------------
 Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.h |  5 +++-
 3 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/Source/Core/Core/HW/SI/SI.h b/Source/Core/Core/HW/SI/SI.h
index 5f8a47afd7..8e2e3afe3b 100644
--- a/Source/Core/Core/HW/SI/SI.h
+++ b/Source/Core/Core/HW/SI/SI.h
@@ -68,6 +68,8 @@ public:
 
   u32 GetPollXLines();
 
+  static constexpr u32 BUFFER_SIZE = 128;
+
 private:
   // SI Interrupt Types
   enum SIInterruptType
@@ -241,7 +243,7 @@ private:
   USIComCSR m_com_csr;
   USIStatusReg m_status_reg;
   USIEXIClockCount m_exi_clock_count;
-  std::array<u8, 128> m_si_buffer{};
+  std::array<u8, BUFFER_SIZE> m_si_buffer{};
 
   Core::System& m_system;
 };
diff --git a/Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.cpp b/Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.cpp
index f002e8f24f..03524214a9 100644
--- a/Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.cpp
+++ b/Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.cpp
@@ -176,14 +176,6 @@ CSIDevice_AMBaseboard::CSIDevice_AMBaseboard(Core::System& system, SIDevices dev
   }
 }
 
-constexpr u32 SI_XFER_LENGTH_MASK = 0x7f;
-
-// Translate [0,1,2,...,126,127] to [128,1,2,...,126,127]
-constexpr s32 ConvertSILengthField(u32 field)
-{
-  return ((field - 1) & SI_XFER_LENGTH_MASK) + 1;
-}
-
 void CSIDevice_AMBaseboard::ICCardSendReply(ICCommand* iccommand, u8* buffer, u32* length)
 {
   iccommand->status = Common::swap16(iccommand->status);
@@ -201,9 +193,9 @@ void CSIDevice_AMBaseboard::ICCardSendReply(ICCommand* iccommand, u8* buffer, u3
 
 void CSIDevice_AMBaseboard::SwapBuffers(u8* buffer, u32* buffer_length)
 {
-  memcpy(m_last[1], buffer, 0x80);     // Save current buffer
-  memcpy(buffer, m_last[0], 0x80);     // Load previous buffer
-  memcpy(m_last[0], m_last[1], 0x80);  // Update history
+  memcpy(m_last[1], buffer, RESPONSE_SIZE);     // Save current buffer
+  memcpy(buffer, m_last[0], RESPONSE_SIZE);     // Load previous buffer
+  memcpy(m_last[0], m_last[1], RESPONSE_SIZE);  // Update history
 
   m_lastptr[1] = *buffer_length;  // Swap lengths
   *buffer_length = m_lastptr[0];
@@ -212,11 +204,12 @@ void CSIDevice_AMBaseboard::SwapBuffers(u8* buffer, u32* buffer_length)
 
 int CSIDevice_AMBaseboard::RunBuffer(u8* buffer, int request_length)
 {
-  const auto& serial_interface = m_system.GetSerialInterface();
-  u32 buffer_length = ConvertSILengthField(serial_interface.GetInLength());
-
   // Debug logging
-  ISIDevice::RunBuffer(buffer, buffer_length);
+  ISIDevice::RunBuffer(buffer, request_length);
+
+  const auto& serial_interface = m_system.GetSerialInterface();
+
+  u32 buffer_length = RESPONSE_SIZE;
 
   u32 buffer_position = 0;
   while (buffer_position < buffer_length)
diff --git a/Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.h b/Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.h
index 4e7be13f00..55de0d357f 100644
--- a/Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.h
+++ b/Source/Core/Core/HW/SI/SI_DeviceAMBaseboard.h
@@ -4,6 +4,7 @@
 #pragma once
 
 #include "Core/HW/MagCard/MagneticCardReader.h"
+#include "Core/HW/SI/SI.h"
 #include "Core/HW/SI/SI_Device.h"
 
 namespace SerialInterface
@@ -175,7 +176,9 @@ private:
     u32 extlen;
   };
 
-  u8 m_last[2][0x80] = {};
+  static constexpr u32 RESPONSE_SIZE = SerialInterfaceManager::BUFFER_SIZE;
+
+  u8 m_last[2][RESPONSE_SIZE] = {};
   u32 m_lastptr[2] = {};
 
   std::array<u16, 2> m_coin{};