feat(shell): add poke command to write a byte to memory

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

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);

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 {