1 files changed, 38 insertions, 0 deletions

diff --git a/src/mailbox.h b/src/mailbox.h
new file mode 100644
index 0000000..e96a4ed
--- /dev/null
+++ b/src/mailbox.h
@@ -0,0 +1,38 @@
+#pragma once
+
+#include <stdint.h>
+
+// The channel takes the lower 4 bits; the data pointer the upper 28. So a mail
+// must be aligned to a 16-byte boundary.
+#define MAIL_ALIGN 16
+
+enum
+{
+  PROPERTY_CHANNEL = 8,
+};
+
+typedef struct Tag {
+  union {
+    uint32_t all;
+    struct {
+      uint16_t command : 12; // Command.
+      uint8_t  type    :  4; // Command type.
+      uint8_t  device  :  4; // Hardware device.
+      uint16_t zeroes  : 12; // Reserved.
+    } id;
+  };
+  uint32_t size;    // Buffer size.
+  uint32_t code;    // Request/response code.
+  uint32_t data[1]; // 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.
+} Mail;
+
+void        mbox_init();
+const Mail* mbox_read(uint8_t channel);
+void        mbox_write(uint8_t channel, const void* mail);
+