Free call to BIOS routine - Revision history

Aoineko at 18:35, 22 September 2026

2026-09-22T18:35:53Z

2026-09-22T18:32:30Z

2026-09-22T18:32:15Z

2026-09-22T18:31:07Z

2026-09-22T18:30:55Z

2022-07-08T22:15:23Z

2022-07-08T22:14:39Z

2022-07-08T22:04:09Z

2022-07-08T22:03:49Z

2022-07-08T22:02:21Z

@@ Line 19: / Line 19: @@
 !	!!__sdcccall(0)	!!__sdcccall(1)	 !!__z88dk_fastcall
 |-
-|colspan="4"|RETURN
+|colspan="4" style="text-align:center;"|RETURN
 |-
 |8 bits	||L	||A	||L
@@ Line 27: / Line 27: @@
 |32 bits	||DE-HL	||HL-DE	||DE-HL
 |-
-|colspan="4"|PARAMETERS
+|colspan="4" style="text-align:center;"|PARAMETERS
 |-
 |8 bits	||Stack	||A	||L

@@ Line 35: / Line 35: @@
 |32 bits	||Stack	||HL-DE	||DE-HL
 |-
-|8 + 8 bits	||Stack	||A + L	||Invalid
+|8 + 8 bits	||Stack	||A + L	||''Invalid''
 |-
-|8 + 16 bits	||Stack	||A + DE	||Invalid
+|8 + 16 bits	||Stack	||A + DE	||''Invalid''
 |-
-|16 + 16 bits	||Stack	||HL + DE	||Invalid
+|16 + 16 bits	||Stack	||HL + DE	||''Invalid''
 |-
-|16 + 8 bits	||Stack	||HL + Stack	||Invalid
+|16 + 8 bits	||Stack	||HL + Stack	||''Invalid''
 |}
 You can found many examples in <tt>engine\src\bios.h</tt>.

@@ Line 15: / Line 15: @@
 Here is a summary of all possible the combinations:
-{| class="wikitable'
+{| class="wikitable"
 |-
 !	!!__sdcccall(0)	!!__sdcccall(1)	 !!__z88dk_fastcall
 |-
-|spancol="4"|RETURN
+|colspan="4"|RETURN
 |-
 |8 bits	||L	||A	||L
@@ Line 27: / Line 27: @@
 |32 bits	||DE-HL	||HL-DE	||DE-HL
 |-
-|spancol="4"|PARAMETERS
+|colspan="4"|PARAMETERS
 |-
-|8 bits	Stack	||A	||L
+|8 bits	||Stack	||A	||L
 |-
 |16 bits	||Stack	||HL	||HL

@@ Line 15: / Line 15: @@
 Here is a summary of all possible the combinations:
-{| style="wikitable'
+{| class="wikitable'
 |-
 !	!!__sdcccall(0)	!!__sdcccall(1)	 !!__z88dk_fastcall

@@ Line 15: / Line 15: @@
 Here is a summary of all possible the combinations:
-<html><img width="900px" src="https://cdn.discordapp.com/attachments/574951023374761988/995082329997443184/unknown.png" /></html>
+{| style="wikitable'
 You can found many examples in <tt>engine\src\bios.h</tt>.

@@ Line 3: / Line 3: @@
 The idea is to "cast" an address with the signature of a C function so that the calling code initializes the registers properly before calling the BIOS function.
-For example, the function <tt>GTSTCK</tt> (<tt>00D5h</tt>) which returns the status of the joystick, takes its input parameter in A and returns its final value in A. Among the possible function signatures, <tt>(u8(*)(u8))</tt> uses these same registers (<tt>u8</tt> is <tt>unsigned char</tt>).
+For example, the function <tt>GTSTCK</tt> (<tt>00D5h</tt>) which returns the status of the joystick, takes its input parameter in A and returns its final value in A. Among the possible function signatures, <tt>(u8(*)(u8))</tt> uses these same registers.
 Thus, with this function definition...

@@ Line 7: / Line 7: @@
 Thus, with this function definition...
   inline u8 Bios_GetJoystickDirection(u8 port) { return ((u8(*)(u8))R_GTSTCK)(port); }
-...the calling code will put the port number into A, call the <tt>GTSTCK</tt> function, then read the result into A.
+...the calling code will put the port number into register A, call the <tt>GTSTCK</tt> function, then read the result into register A.
 Since the function is inline, we gain C typing verification, while having zero C overhead.

@@ Line 11: / Line 11: @@
 Since the function is inline, we gain C typing verification, while having zero C overhead.
-Obviously, this only works with BIOS routines that use registers for which there is a C function signature. There are few of them, but by playing with the <tt>sdcccall1</tt> and <tt>z88dk_fastcall</tt> calling conventions, we still have some possibilities.
+Obviously, this only works with BIOS routines that use registers for which there is a C function signature. There are few of them, but by playing with the <tt>sdcccall1</tt> and <tt>z88dk_fastcall</tt> calling conventions, we still have some possibilities. In the case of a <tt>z88dk_fastcall</tt> signature you have to use a <tt>typedef</tt> to define the signature before you can use it.
 Here is a summary of all possible the combinations:

← Older revision		Revision as of 22:02, 8 July 2022
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	<html><img width="900px" src="https://cdn.discordapp.com/attachments/574951023374761988/995082329997443184/unknown.png" /></html>		<html><img width="900px" src="https://cdn.discordapp.com/attachments/574951023374761988/995082329997443184/unknown.png" /></html>
		+
		+	You can found many examples in <tt>engine\src\bios.h</tt>.