From e4d111a55e8f1d9b49e67dc98d9d2cdf418d9221 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Tue, 7 Sep 2021 16:46:30 +0200
Subject: Add working framebuffer request

Resources:
- https://jsandler18.github.io/extra/prop-channel.html
- https://jsandler18.github.io/extra/mailbox.html
- https://github.com/bztsrc/raspi3-tutorial/tree/master/09_framebuffer
- https://www.youtube.com/watch?v=hSJWbmiQfck
---
 src/common.h | 105 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 src/main.c   |   5 +--
 src/ppu.c    |  54 ++++++++++++++++++++++++++++++
 3 files changed, 160 insertions(+), 4 deletions(-)
 create mode 100644 src/ppu.c

diff --git a/src/common.h b/src/common.h
index a6af346..0bd365a 100644
--- a/src/common.h
+++ b/src/common.h
@@ -60,11 +60,9 @@ static inline void
 gpio_pin_set_func(u8 pin, GpioFunc func) {
     u8 start = (pin * 3) % 30;
     u8 reg = pin / 10;
-
     u32 selector = GPIO->func_select[reg];
     selector &= ~(7 << start);
     selector |= (func << start);
-
     GPIO->func_select[reg] = selector;
 }
 
@@ -144,4 +142,107 @@ uart_puts(char *s) {
     }
 }
 
+static inline void
+uart_hex(unsigned int d) {
+    unsigned int n;
+    uart_puts("0x");
+    for(int c = 28; c >= 0; c -= 4) {
+        n = (d>>c) & 0xF;
+        n += n> 9 ? 0x37 : 0x30;
+        uart_putc(n);
+    }
+}
+
+//
+// VideoCore Mailboxes.
+//
+
+typedef struct MboxTagHeader {
+    u32 id;
+    u32 buf_size;
+    u32 code;
+} MboxTagHeader;
+
+typedef struct MboxScreenTag {
+    MboxTagHeader header;
+    u32 width;
+    u32 height;
+} MboxScreenTag;
+
+typedef struct MboxDepthTag {
+    MboxTagHeader header;
+    u32 depth;
+} MboxDepthTag;
+
+typedef struct MboxFramebufferTag {
+    MboxTagHeader header;
+    u32 fb_addr;
+    u32 fb_size;
+} MboxFramebufferTag;
+
+typedef struct MboxFramebufferRequest {
+    u32 buf_size;
+    u32 code;
+    MboxScreenTag screen_tag;
+    MboxScreenTag virtual_screen_tag;
+    MboxDepthTag depth_tag;
+    MboxFramebufferTag framebuffer_tag;
+    u32 end_tag;
+    u8 padding[8];
+} MboxFramebufferRequest;
+
+typedef struct MailboxRegs {
+    vu32 read;
+    vu32 reserved[5];
+    vu32 status;
+    vu32 config;
+    vu32 write;
+} MailboxRegs;
+
+#define MBOX ((MailboxRegs *)(MEM_BASE + 0x0000B880))
+
+typedef enum MboxChannels {
+    MBOX_CH_POWER = 0,
+    MBOX_CH_FB    = 1,
+    MBOX_CH_VUART = 2,
+    MBOX_CH_VCHIQ = 3,
+    MBOX_CH_LEDS  = 4,
+    MBOX_CH_BTNS  = 5,
+    MBOX_CH_TOUCH = 6,
+    MBOX_CH_COUNT = 7,
+    MBOX_CH_PROP  = 8,
+} MboxChannels;
+
+// Property channel response type.
+#define MBOX_REQUEST      0
+#define MBOX_RESPONSE_OK  0x80000000
+#define MBOX_RESPONSE_ERR 0x80000001
+
+// Mailbox status codes.
+#define MBOX_FULL  0x80000000
+#define MBOX_EMPTY 0x40000000
+
+static inline void
+mb_write(u8 channel, void *data) {
+    while(MBOX->status & MBOX_FULL);
+    MBOX->write = ((uintptr_t)data & ~0xF) | (channel & 0xF);
+}
+
+static inline u32
+mb_read(u8 channel) {
+    while(true) {
+        while(MBOX->status & MBOX_EMPTY);
+        u32 data = MBOX->read;
+        if ((u8)(data & 0xF) == channel) {
+            return data & 0xFFFFFFF0;
+        }
+    }
+}
+
+static inline int
+mb_call(unsigned char ch, void *msg) {
+    mb_write(ch, msg);
+    return mb_read(ch);
+}
+
 #endif // COMMON_RPIBM_H
diff --git a/src/main.c b/src/main.c
index aac605b..22723c0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,13 +1,14 @@
 #include "common.h"
+#include "ppu.c"
 
 void main(void) {
     // Initialize uart.
     uart_init();
 
-    uart_puts("Hello World!\n");
+    ppu_init();
 
-    // Echo input to standard output.
     while(1) {
+        // Echo input to standard output.
         uart_putc(uart_getc());
     }
 }
diff --git a/src/ppu.c b/src/ppu.c
new file mode 100644
index 0000000..99574d7
--- /dev/null
+++ b/src/ppu.c
@@ -0,0 +1,54 @@
+#include "common.h"
+
+static u32 *framebuffer = 0;
+
+void
+ppu_init(void) {
+    static MboxFramebufferRequest fb_request = {
+        .buf_size = 96,
+        .code = MBOX_REQUEST,
+        .screen_tag = {
+            .header = {
+                .id = 0x48003,
+                .buf_size = 8,
+            },
+            .width = 1024,
+            .height = 1024,
+        },
+        .virtual_screen_tag = {
+            .header = {
+                .id = 0x48004,
+                .buf_size = 8,
+            },
+            .width = 1024,
+            .height = 1024,
+        },
+        .depth_tag = {
+            .header = {
+                .id = 0x48005,
+                .buf_size = 4,
+            },
+            .depth = 32,
+        },
+        .framebuffer_tag = {
+            .header = {
+                .id = 0x40001,
+                .buf_size = 8,
+            },
+            .fb_addr = 0,
+            .fb_size = 0,
+        }
+    };
+
+    if (mb_call(MBOX_CH_PROP, &fb_request)
+            && fb_request.depth_tag.depth == 32
+            && fb_request.framebuffer_tag.fb_addr != 0) {
+        fb_request.framebuffer_tag.fb_addr &= 0x3FFFFFFF;
+        framebuffer = (u32*)((uintptr_t)fb_request.framebuffer_tag.fb_addr);
+        for (size_t i = 0; i < 1024 * 100; i++) {
+            framebuffer[i] = 0xffaa22; // 0xBBGGRR
+        }
+    } else {
+        uart_puts("Unable initialize framebuffer\n");
+    }
+}
-- 
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