From 7f14bcb05652926f2e2d6b66c8b7c90f0a7be962 Mon Sep 17 00:00:00 2001
From: kudasai <47227786+kudasaixc@users.noreply.github.com>
Date: Sat, 4 Jul 2026 17:29:52 +0200
Subject: [PATCH] feat(shell): add poke command to write a byte to memory

Complements the existing peek command. mmu_debug_poke mirrors
mmu_debug_peek: it writes a byte through a volatile pointer and reports
the result on both the VGA terminal and the serial log. The shell
command reuses htoi for parsing and validates argc.

Usage: poke <hex address> <hex value>
Example: poke B8000 41  -> writes 'A' to the top-left VGA cell.
---
 src/include/mm.h   |  1 +
 src/kernel/shell.c | 12 +++++++++++-
 src/mm/mmu.zig     | 19 ++++++++++++++++++-
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/include/mm.h b/src/include/mm.h
index d0195c5..9bfb1dd 100644
--- a/src/include/mm.h
+++ b/src/include/mm.h
@@ -19,5 +19,6 @@ extern void mmu_map_page(uint32_t phys_addr, uint32_t virt_addr, bool is_writeab
 
 extern void mmu_view_mappings(void);
 extern void mmu_debug_peek(uint32_t addr);
+extern void mmu_debug_poke(uint32_t addr, uint8_t value);
 
 #endif
diff --git a/src/kernel/shell.c b/src/kernel/shell.c
index 575ab67..6b7c6fc 100644
--- a/src/kernel/shell.c
+++ b/src/kernel/shell.c
@@ -93,6 +93,7 @@ static void shell_execute(char *cmd) {
     terminal_writestring("mia     - force a Page Fault for MMU testing\n");
     terminal_writestring("mmap    - print current virtual memory mappings\n");
     terminal_writestring("peek    - read and print memory at a given hex address\n");
+    terminal_writestring("poke    - write a hex byte at a given hex address\n");
     terminal_writestring("echo    - repeats your input to the console\n");
     terminal_writestring("crash   - make the machine freeze (fun cmd)\n\n");
   }
@@ -247,7 +248,16 @@ static void shell_execute(char *cmd) {
   else if (strcmp(cmd_name, "peek") == 0) {
     uint32_t addr = htoi(args[1]);
     mmu_debug_peek(addr);
-	
+
+  }
+  else if (strcmp(cmd_name, "poke") == 0) {
+    if (argc != 3) {
+      terminal_writestring("usage: poke <hex address> <hex value>\n");
+      return;
+    }
+    uint32_t addr = htoi(args[1]);
+    uint8_t value = (uint8_t) htoi(args[2]);
+    mmu_debug_poke(addr, value);
   }
   else if (strcmp(cmd_name, "memtest") == 0) {
     char *a = malloc(32);
diff --git a/src/mm/mmu.zig b/src/mm/mmu.zig
index ded420f..96c49a6 100644
--- a/src/mm/mmu.zig
+++ b/src/mm/mmu.zig
@@ -202,7 +202,24 @@ export fn mmu_debug_peek(addr: usize) void {
     serial_write_string("Value found: ");
     print_hex(value);
     serial_write_string("\r\n");
-	
+
+}
+
+export fn mmu_debug_poke(addr: usize, value: u8) void {
+    const ptr = @as(*volatile u8, @ptrFromInt(addr));
+    ptr.* = value;
+
+    terminal_writestring("Wrote ");
+    terminal_print_hex(value);
+    terminal_writestring(" at ");
+    terminal_print_hex(@as(u32, @truncate(addr)));
+    terminal_writestring("\n");
+
+    serial_write_string("\r\n[DEBUG] Poked ");
+    print_hex(value);
+    serial_write_string(" at ");
+    print_hex(addr);
+    serial_write_string("\r\n");
 }
 
 export fn mmu_handle_page_fault(error_code: u32) void {