From 636e5787dec7bbdbcbb0c776e8d5fb7fcb06a7c3 Mon Sep 17 00:00:00 2001
From: giomba <giomba@glgprograms.it>
Date: Fri, 13 Oct 2023 21:39:40 +0200
Subject: [PATCH] Add documentation about C/ASM calling conventions.

---
 README.md  | 41 +++++++++++++++++++++++++++++++++++++++++
 src/main.c | 16 ++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/README.md b/README.md
index bad3e2e..554e8bf 100644
--- a/README.md
+++ b/README.md
@@ -5,3 +5,44 @@ Demo for the Sanco 800x.
 The purpose of this demo is mainly to thinker with the hardware of the mentioned computer, since we are reverse-engineering it, and even writing an emulator.
 
 This repository is part of the [CEDA project](https://github.com/GLGPrograms/ceda-home) by [Retrofficina GLG Programs](https://retrofficina.glgprograms.it/).
+
+## C/ASM calling conventions
+Because the folks at z88dk were not able to put this plain and simple table
+in their messy documentation :smile:
+
+### Prologue
+```
+    push    ix
+    ld      ix,$0000
+    add     ix,sp
+```
+
+### Parameters stack
+```
+    uint8_t
+        ix+$04
+
+    uint8_t, uint8_t
+        ix+$04, ix+$05
+```
+
+### Access call parameters
+```
+    ld      a,(ix+$04)
+    ld      a,(ix+$05)
+```
+
+### Return value
+```
+    uint32_t    de (msb), hl (lsb)
+    uint16_t    hl
+    uint8_t     l
+    void*       hl
+```
+
+### Epilogue
+```
+    pop     ix
+    ret
+```
+
diff --git a/src/main.c b/src/main.c
index 699bde2..db728f9 100644
--- a/src/main.c
+++ b/src/main.c
@@ -12,3 +12,19 @@ int main(void) {
 
     return 0;
 }
+
+uint8_t ret_u8(void) {
+    return 0x01;
+}
+
+uint16_t ret_u16(void) {
+    return 0x0123;
+}
+
+uint32_t ret_u32(void) {
+    return 0x01234567;
+}
+
+void *ret_ptr(void) {
+    return (void *)0x1234;
+}