From c099bcb7402421985e6e8c025e8cde591eaa073a Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Tue, 14 Oct 2025 17:54:17 -0700
Subject: Add MAIL_T macro; read framebuffer allocation response

---
 src/framebuffer.c | 21 +++++++++++++++++++--
 src/mailbox.h     | 12 +++++++++---
 src/uart.c        |  2 +-
 3 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/src/framebuffer.c b/src/framebuffer.c
index e3303b6..c3845b1 100644
--- a/src/framebuffer.c
+++ b/src/framebuffer.c
@@ -2,6 +2,7 @@
 
 #include <mailbox.h>
 
+#include <stddef.h>
 #include <stdint.h>
 
 #define WIDTH     640
@@ -9,8 +10,15 @@
 #define DEPTH      32
 #define ALIGNMENT  16 // Framebuffer byte alignment.
 
+typedef struct Framebuffer {
+  volatile void* pixels;
+  size_t         size;
+} Framebuffer;
+
+static Framebuffer framebuffer = {};
+
 bool framebuffer_init(uint32_t* error) {
-  volatile __attribute__((aligned(MAIL_ALIGN))) uint32_t ConfigureScreen[20] = {
+  MAIL_T uint32_t ConfigureScreen[20] = {
     80, // Size in bytes, aligned to MAIL_ALIGN.
     MAILBOX_REQUEST,
     TAG_FRAMEBUFFER_SET_PHYSICAL_SCREEN_SIZE, 8, MAILBOX_REQUEST, WIDTH, HEIGHT,
@@ -25,7 +33,7 @@ bool framebuffer_init(uint32_t* error) {
     goto end;
   }
   
-  volatile __attribute__((aligned(MAIL_ALIGN))) uint32_t InitFramebuffer[8] = {
+  MAIL_T uint32_t InitFramebuffer[8] = {
     32, // Size in bytes, aligned to MAIL_ALIGN.
     MAILBOX_REQUEST,
     TAG_FRAMEBUFFER_ALLOCATE, 8, MAILBOX_REQUEST, ALIGNMENT, 0,
@@ -33,6 +41,15 @@ bool framebuffer_init(uint32_t* error) {
   };
   mbox_write(PROPERTY_CHANNEL, InitFramebuffer);
   response = mbox_read(PROPERTY_CHANNEL);
+  if (response->code != MAILBOX_SUCCESS) {
+    goto end;
+  }
+  
+  // The input mail is overwritten with the response.
+  //   u32 fb base address
+  //   u32 fb size
+  framebuffer.pixels = (void*)(uintptr_t)InitFramebuffer[5];
+  framebuffer.size   = InitFramebuffer[6];
   
 end:
   *error = response->code;
diff --git a/src/mailbox.h b/src/mailbox.h
index b35c7a6..2104265 100644
--- a/src/mailbox.h
+++ b/src/mailbox.h
@@ -1,3 +1,9 @@
+/*
+References:
+  https://github-wiki-see.page/m/raspberrypi/firmware/wiki/Mailbox-property-interface
+  https://jsandler18.github.io/extra/prop-channel.html
+  https://jsandler18.github.io/extra/mailbox.html
+*/
 #pragma once
 
 #include <stdint.h>
@@ -6,6 +12,9 @@
 // must be aligned to a 16-byte boundary.
 #define MAIL_ALIGN 16
 
+// Type prefix for data arrays used as mail.
+#define MAIL_T volatile __attribute__((aligned(MAIL_ALIGN)))
+
 enum
 {
   PROPERTY_CHANNEL = 8,
@@ -55,9 +64,6 @@ typedef struct __attribute__((aligned(MAIL_ALIGN))) Mail {
   Tag      tags[];  // Variable quantity.
 } Mail;
 
-// TODO: Remove? Unused.
-#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, volatile const void* mail);
diff --git a/src/uart.c b/src/uart.c
index 3b107f4..f8be797 100644
--- a/src/uart.c
+++ b/src/uart.c
@@ -35,7 +35,7 @@ enum
 };
 
 // A mailbox message with set clock rate of PL011 to 3MHz tag.
-static const uint32_t __attribute__((aligned(MAIL_ALIGN))) UART_SET_CLK[9] = {
+static const MAIL_T uint32_t UART_SET_CLK[9] = {
   9*4, 0, 0x38002, 12, 8, 2, 3000000, 0, 0
 };
 
-- 
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