bios: stub calls interrupt number; simplified bios.ha main interface

Instead of having the bios.call stub calling a function, make it directly call an interrupt that is
changed dynamically by modifying the code at runtime.
Simplify the bios.ha interface and document it.

Next up: implementing a high level drive interface for the BIOS using BIOS interrupts

1 files changed, 41 insertions, 0 deletions

diff --git a/bios/bios.ha b/bios/bios.ha
new file mode 100644
index 0000000..afae0f6
--- /dev/null
+++ b/bios/bios.ha
@@ -0,0 +1,41 @@
+// Struct defining the contents of the register state used
+// for bios calls
+export type state = struct {
+	@offset(0) eax: u32,
+	@offset(4) ebx: u32,
+	@offset(8) ecx: u32,
+	@offset(12) edx: u32,
+	@offset(16) edi: u32,
+	@offset(20) esi: u32,
+	@offset(24) ds: u16,
+	@offset(26) es: u16,
+	@offset(28) ss: u16,
+	@offset(30) gs: u16,
+	@offset(32) fs: u16
+};
+
+// The set real mode registers
+export let regs: state;
+
+// The address of a 512 bytes workspace that is located below 0xFFFFF and can be used to store the results
+// of various bios calls
+export const @symbol("_ws") ws: u16;
+
+// The boot drive number as given by the BIOS at boot time
+export const @symbol("drive_no") drive_number: u8;
+
+// The amount of sectors per track that the boot drive has
+export const @symbol("drive_spt") drive_sectors_per_track: u8;
+
+// The amount of heads that the boot drive has
+export const @symbol("drive_heads") drive_heads: u8;
+
+// Clears the BIOS mode registers
+export fn clearregs() void = {
+	regs = state {
+		...
+	};
+};
+
+// Call a BIOS interrupt
+export fn call(intno: u8) void;