5 files changed, 80 insertions, 5 deletions

diff --git a/src/framebuffer.c b/src/framebuffer.c
new file mode 100644
index 0000000..a90bcaa
--- /dev/null
+++ b/src/framebuffer.c
@@ -0,0 +1,30 @@
+#include <framebuffer.h>
+
+#include <mailbox.h>
+
+#include <stdint.h>
+
+#define WIDTH  640
+#define HEIGHT 480
+#define DEPTH   32
+
+bool framebuffer_init(uint32_t* error) {
+  volatile const Mail* mail;
+  
+  volatile __attribute__((aligned(MAIL_ALIGN))) uint32_t InitFramebuffer[] = {
+    80, // Size in bytes aligned to MAIL_ALIGN(16).
+    MAILBOX_REQUEST,
+    TAG_FRAMEBUFFER_SET_PHYSICAL_SCREEN_SIZE, 8, MAILBOX_REQUEST, WIDTH, HEIGHT,
+    TAG_FRAMEBUFFER_SET_VIRTUAL_SCREEN_SIZE,  8, MAILBOX_REQUEST, WIDTH, HEIGHT,
+    TAG_FRAMEBUFFER_SET_DEPTH,                4, MAILBOX_REQUEST, DEPTH,
+    TAG_END,
+    0, 0, 0 // Pad.
+  };
+
+  mbox_write(PROPERTY_CHANNEL, InitFramebuffer);
+  while ((mail = mbox_read(PROPERTY_CHANNEL)) != (volatile Mail*)(InitFramebuffer));
+  
+  *error = mail->code;
+  return mail->code == MAILBOX_SUCCESS;
+}
+
diff --git a/src/framebuffer.h b/src/framebuffer.h
new file mode 100644
index 0000000..d2d57cd
--- /dev/null
+++ b/src/framebuffer.h
@@ -0,0 +1,7 @@
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+bool framebuffer_init(uint32_t* error);
+
diff --git a/src/kernel.c b/src/kernel.c
index 4296aa7..ac803cc 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -1,3 +1,4 @@
+#include <framebuffer.h>
 #include <mailbox.h>
 #include <mmio.h>
 #include <raspi.h>
@@ -10,14 +11,26 @@ static void halt() {
 }
 
 void main() {
+  bool     success = true;
+  uint32_t error   = -1;
+  
   const int raspi = raspi_init();
   mmio_init(raspi); // Must be initialized before other peripherals.
   
   mbox_init();
   uart_init(raspi);
+  success = framebuffer_init(&error);
+  if (!success) {
+    uart_print("Failed to initialize framebuffer\n");
+    if (error == MAILBOX_DELIVERY_ERROR) {
+      uart_print("MAILBOX_DELIVERY_ERROR\n");
+    }
+    goto end;
+  }
   
   uart_print("Hello world!\n");
   
+end:
   halt();
 }
 
diff --git a/src/mailbox.c b/src/mailbox.c
index eaf0955..aacb747 100644
--- a/src/mailbox.c
+++ b/src/mailbox.c
@@ -21,7 +21,7 @@ static inline const void* msg_data(Message msg) {
   return (const void*)((uintptr_t)(msg >> 4));
 }
 
-static inline Message msg_make(uint8_t channel, const void* data) {
+static inline Message msg_make(uint8_t channel, volatile const void* data) {
   return ((uintptr_t)(data) << 4) | (channel & 0xf);
 }
 
@@ -64,7 +64,7 @@ const Mail* mbox_read(uint8_t channel) {
   return (const Mail*)(msg_data(msg));
 }
 
-void mbox_write(uint8_t channel, const void* mail) {
+void mbox_write(uint8_t channel, volatile const void* mail) {
   // Wait until the outbox is clear.
   while (outbox_full(pMailbox));
   // Send the mail.
diff --git a/src/mailbox.h b/src/mailbox.h
index e96a4ed..3cca366 100644
--- a/src/mailbox.h
+++ b/src/mailbox.h
@@ -11,6 +11,29 @@ enum
   PROPERTY_CHANNEL = 8,
 };
 
+enum
+{
+  MAILBOX_REQUEST  = 0,
+  MAILBOX_RESPONSE = 1,
+};
+
+enum
+{
+  MAILBOX_DELIVERY_ERROR = 0,
+  MAILBOX_ERROR          = 0x80000001,
+  MAILBOX_SUCCESS        = 0x80000000,
+};
+
+enum
+{
+  TAG_END                                  = 0,
+  TAG_FRAMEBUFFER_ALLOCATE                 = 0x00040001,
+  TAG_FRAMEBUFFER_RELEASE                  = 0x00048001,
+  TAG_FRAMEBUFFER_SET_PHYSICAL_SCREEN_SIZE = 0x00048003,
+  TAG_FRAMEBUFFER_SET_VIRTUAL_SCREEN_SIZE  = 0x00048004,
+  TAG_FRAMEBUFFER_SET_DEPTH                = 0x00048005,
+};
+
 typedef struct Tag {
   union {
     uint32_t all;
@@ -23,16 +46,18 @@ typedef struct Tag {
   };
   uint32_t size;    // Buffer size.
   uint32_t code;    // Request/response code.
-  uint32_t data[1]; // Buffer data.
+  uint32_t data[];  // Buffer data.
 } Tag;
 
 typedef struct __attribute__((aligned(MAIL_ALIGN))) Mail {
   uint32_t size;    // Buffer size.
   uint32_t code;    // Request/response code.
-  Tag      tags[1]; // Variable quantity.
+  Tag      tags[];  // Variable quantity.
 } Mail;
 
+#define MAIL_SIZE(TYPE) (sizeof(TYPE) + (2 * sizeof(uint32_t)))
+
 void        mbox_init();
 const Mail* mbox_read(uint8_t channel);
-void        mbox_write(uint8_t channel, const void* mail);
+void        mbox_write(uint8_t channel, volatile const void* mail);