vault backup: 2022-08-01 11:30:26

content/notes/07-6809-advanced.md

@@ -6,7 +6,7 @@ tags:
 - cosc204
 ---
 
-10 addressing modes
+# addressing modes
 - implied `inca`
 - immediate `lda #$00`
 - extended `LDA $31FE` 
@@ -25,6 +25,50 @@ tags:
 - program counter relative `LDA TABLE,PCR ; A = the value stored at TABLE`
 	- if all memory references are relative, then the program cna be loaded anywhere is memory, and will still work. It is said to be **relocatable**
 
+![operand cheat sheet](https://i.imgur.com/mA7Y8bE.png)
 
- 
+# Calling conventions
+all global vars. this is discouraged in high level languages
 
+The calling convention is the set of rules that describe 
+- How to pass parameters 
+- How to return a result 
+- Which registers a routine may alter
+
+## CMOC
+a 6809 C compiler
+
+callling conventions
+- A routine must preserve Y, U, S and DP 
+- A routine may change A, B, X and CC 
+
+- Parameters are pushed on the stack in the reverse order 
+- The caller pops them off the stack after the call 
+
+- char parameters are promoted to int 
+- unsigned char are promoted to unsigned int 
+
+- Return 8-but values in B 
+- Return 16-bit values in D 
+
+- We’re not going to talk about passing a struct by value
+
+### example in C
+
+``` c
+uint16_t two_params(uint8_t first, uint16_t second) { 
+	return first + second; 
+} 
+
+uint16_t call_one(void) { 
+	return two_params(204, 431); 
+}
+```
+
+```
+LDD #$01AF ;
+decimal 431 PSHS B,A ;
+argument 2, int CLRA LDB #$CC ;
+decimal 204 PSHS B,A ;
+argument 1, int LBSR _two_params
+```