From 495bffdc7c11c94843e8b58e73d6dae46910ed80 Mon Sep 17 00:00:00 2001
From: Rob Taylor <rob.taylor@chipflow.io>
Date: Thu, 18 Dec 2025 23:50:32 +0000
Subject: [PATCH] feat: Write UART output to uart.log file for VS Code
 extension
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Add open_uart_log() and close_uart_log() functions to write UART
output to a dedicated file at PROJECT_ROOT/uart.log. The file is
flushed after each character for real-time monitoring by the
ChipFlow VS Code extension.

This enables the extension's UART Console panel to display
simulation output in real-time by watching the log file.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 chipflow/common/sim/main.cc.jinja |  2 ++
 chipflow/common/sim/models.cc     | 28 ++++++++++++++++++++++++++--
 chipflow/common/sim/models.h      |  4 ++++
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/chipflow/common/sim/main.cc.jinja b/chipflow/common/sim/main.cc.jinja
index cd72b861..b7097ad5 100644
--- a/chipflow/common/sim/main.cc.jinja
+++ b/chipflow/common/sim/main.cc.jinja
@@ -26,6 +26,7 @@ int main(int argc, char **argv) {
         std::cerr << "Waiting for debugger on " << agent.start_debugging() << std::endl;
 
     open_event_log(BUILD_DIR "/sim/events.json");
+    open_uart_log(PROJECT_ROOT "/uart.log");
     open_input_commands(PROJECT_ROOT "/design/tests/input.json");
 
     unsigned timestamp = 0;
@@ -74,5 +75,6 @@ int main(int argc, char **argv) {
         tick();
 
     close_event_log();
+    close_uart_log();
     return 0;
 }
diff --git a/chipflow/common/sim/models.cc b/chipflow/common/sim/models.cc
index 0aabda4f..b4863aca 100644
--- a/chipflow/common/sim/models.cc
+++ b/chipflow/common/sim/models.cc
@@ -86,6 +86,9 @@ void open_input_commands(const std::string &filename) {
 
 static std::ofstream event_log;
 
+// UART log file for VS Code extension
+static FILE *uart_log = nullptr;
+
 void open_event_log(const std::string &filename) {
     event_log.open(filename);
     if (!event_log) {
@@ -135,6 +138,22 @@ void close_event_log() {
     }
 }
 
+void open_uart_log(const std::string &filename) {
+    uart_log = fopen(filename.c_str(), "w");
+    if (!uart_log) {
+        fprintf(stderr, "WARNING: failed to open UART log file: %s\n", filename.c_str());
+    } else {
+        fprintf(stderr, "Logging UART to file: %s\n", filename.c_str());
+    }
+}
+
+void close_uart_log() {
+    if (uart_log) {
+        fclose(uart_log);
+        uart_log = nullptr;
+    }
+}
+
 namespace models {
 
 // SPI flash
@@ -246,10 +265,15 @@ void uart::step(unsigned timestamp) {
                 s.rx_sr = (tx ? 0x80U : 0x00U) | (s.rx_sr >> 1U);
             }
             if (bit == 8) {
-                // print to console
+                // print to console and log file
                 log_event(timestamp, name, "tx", json(s.rx_sr));
-                if (name == "uart_0")
+                if (name == "uart_0") {
                     fprintf(stderr, "%c", char(s.rx_sr));
+                    if (uart_log) {
+                        fprintf(uart_log, "%c", char(s.rx_sr));
+                        fflush(uart_log);  // Flush for real-time watching
+                    }
+                }
             }
             if (bit == 9) {
                 // end
diff --git a/chipflow/common/sim/models.h b/chipflow/common/sim/models.h
index 8147bddc..69806a8c 100644
--- a/chipflow/common/sim/models.h
+++ b/chipflow/common/sim/models.h
@@ -30,6 +30,10 @@ void log_event(unsigned timestamp, const std::string &peripheral, const std::str
 std::vector<action> get_pending_actions(const std::string &peripheral);
 void close_event_log();
 
+// UART log file for VS Code extension real-time monitoring
+void open_uart_log(const std::string &filename);
+void close_uart_log();
+
 namespace models {