working dos vga writes!

Player/Display/dos.c

@@ -1,3 +1,4 @@
+#include "../../Common/def.h"
 #include "display.h"
 #include <fcntl.h>
 #include <stdbool.h>
@@ -259,6 +260,17 @@ static inline bool set_segment_rights(uint16_t selector, bool read,
   return !carry_clear;
 }
 
+static inline intptr_t get_segment_base_address(uint16_t selector) {
+  bool carry_clear;
+  uint16_t high, low;
+  __asm__ volatile("int $0x31"
+                   : "=@ccnc"(carry_clear), "=c"(high), "=d"(low)
+                   : "a"(0x0006), "b"(selector)
+                   : "memory", "cc");
+  // return carry_clear ? 0 : (((intptr_t)high << 16) | (intptr_t)low);
+  return ((intptr_t)high << 16) | (intptr_t)low;
+}
+
 static inline void use_segment(uint16_t selector) {
   __asm__ volatile("" : "=S"(selector)::);
 }
@@ -271,40 +283,19 @@ static inline void print_to_console(char *const str) {
 
 static uint32_t test = 0x1420124;
 
-// extern int plr_display_dos_main(int argc, char *argv[]) {
 extern int plr_display_dos_main(void) {
-  print_to_console("Fuck you stupid shit");
-  return -1;
-
-  uint16_t base = alloc_ldt_descriptor();
-  if (!base) {
-    print_to_console("Cannot allocate LDT descriptor");
+  /* Fat DS trick, see __djgpp_nearptr_enable() */
+  unsigned short ds_selector;
+  asm("movw %%ds, %0" : "=r"(ds_selector));
+  set_segment_limit(ds_selector, 0xFFFFFFFF);
+  intptr_t baseaddr = get_segment_base_address(ds_selector);
+  if (baseaddr == 0)
     return -1;
-  }
 
-  if (!set_segment_base_address(base, 0xA0000)) {
-    print_to_console("Cannot set LDT base address");
-    return -1;
-  }
-
-  if (!set_segment_limit(base, 0x10000)) {
-    print_to_console("Cannot set LDT limit");
-    return -1;
-  }
-
-  use_segment(base);
-
-  // char *volatile buf = (void *)(intptr_t)0xA0000; // VGA memory address
-  // char *buf = map_physical_address(0xA0000, 0x10000); // VGA memory
-  char *buf = map_physical_address(0xA0000, 0x10000); // VGA memory
-  // address
-  if (!buf)
-    return -1;
-  int x, y;
-
-  // if (!buf)
-  //   return -1;
+  unsigned char *volatile buf =
+      (unsigned char *)((intptr_t)0xA0000 - baseaddr); // VGA memory address
 
+  /* TODO: Make VESA work for sweet sweet 640x480. */
   // unsigned char saved_mode = get_video_mode(); // Save original mode
   // set_vesa_video_mode(MODE_VESA_640_480_8); // Set our VGA mode
   set_video_mode(MODE_VGA_320_200_8); // Set our VGA mode
@@ -327,6 +318,7 @@ extern int plr_display_dos_main(void) {
   // wait_for_key();
   // set_video_mode(saved_mode); // Restore original mode
 
+  int x, y;
   while (1) {
     for (y = 0; y < HEIGHT; y++) {
       for (x = 0; x < WIDTH; x++) {
@@ -339,7 +331,6 @@ extern int plr_display_dos_main(void) {
       }
     }
     // writetest();
-    __asm__ volatile("int $0x16" : : "a"(0x00) : "memory", "cc");
   }
 
   // dpmi_regs = (struct dpmi_regs){.eax = 0x00004C00};