From 963aebd9488de1989e7b651d0801fd10428aabcd Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Sun, 4 Apr 2021 21:41:22 +0000
Subject: [PATCH] Add uartctrl.rom: Control PC via COM1 attached terminal

---
 Makefile         |   3 +
 rom/uartctrl.asm | 325 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 328 insertions(+)
 create mode 100644 rom/uartctrl.asm

diff --git a/Makefile b/Makefile
index 00bdacf..eab91cb 100644
--- a/Makefile
+++ b/Makefile
@@ -82,3 +82,6 @@ qemu-floppy5: fd360.img $(ROMS)
 
 qemu-hdd: hdd.img $(ROMS)
 	$(QEMU) $(QEMU_ARGS) -boot c -hda hdd.img
+
+qemu-uartctrl: uartctrl.rom
+	$(QEMU) $(QEMU_ARGS) -option-rom uartctrl.rom -serial stdio
diff --git a/rom/uartctrl.asm b/rom/uartctrl.asm
new file mode 100644
index 0000000..1a8f70d
--- /dev/null
+++ b/rom/uartctrl.asm
@@ -0,0 +1,325 @@
+	cpu 8086
+	org 0x0000
+
+	; configuration for the uart chip for i/o
+%define uart 0x3F8
+%define irq 4
+%define clock 115200
+%define baud 9600
+
+data	equ (uart + 0) ; data register
+ier	equ (uart + 1)
+fcr	equ (uart + 2)
+isr	equ (uart + 2)
+lcr	equ (uart + 3)
+mcr	equ (uart + 4)
+lsr	equ (uart + 5) ; line status register
+msr	equ (uart + 6)
+
+absolute 0xE0 ; data in bios data area
+pstate	resw 1 ; parser resume offset
+parg	resb 1 ; accumulator for numerical CSI arguments
+section .text
+
+	db 0x55, 0xAA
+	db 0x00
+	jmp init
+
+%defstr	uart_s uart
+%defstr baud_s baud
+banner	db "nero uartctrl: port ", uart_s, " irq ", irq + 0x30," baud ", baud_s, 0x0A, 0x0D, 0
+
+init	push ax
+	push dx
+	push bx
+	push si
+	push ds
+
+	; set dlab
+	mov dx, lcr
+	in al, dx
+	or al, 0x80
+	out dx, al
+	; set divisor
+	mov cx, (clock / baud)
+	; low byte
+	mov dx, (uart + 0)
+	mov al, cl
+	out dx, al
+	; high byte
+	mov dx, (uart + 1)
+	mov al, ch
+	out dx, al
+	; disable dlab
+	mov dx, lcr
+	in al, dx
+	and al, 0x7F
+	out dx, al
+	; disable fifo
+	mov dx, fcr
+	mov al, 0
+	out dx, al
+	; enable RX interrupt
+	mov dx, ier
+	mov al, 1
+	out dx, al
+	; set line modes (8 bits, no parity, 1 stopbit)
+	mov dx, lcr
+	mov al, 3
+	out dx, al
+	; set modem control lines (unused)
+	mov dx, mcr
+	mov al, 8
+	out dx, al
+
+	; hook boot interrupt
+	xor ax, ax
+	mov ds, ax
+	mov word [4*0x19], int19
+	mov word [4*0x19+2], cs
+
+	; hook video services
+	; keep original ptr in intvec 47h for chaining
+	mov ax, int10
+	mov bx, cs
+	xchg word [4*0x10], ax
+	xchg word [4*0x10+2], bx
+	mov word [4*0x47], ax
+	mov word [4*0x47+2], bx
+
+	; hook uart irq
+	mov word [4*(0x08+irq)], intu
+	mov word [4*(0x08+irq)+2], cs
+
+	; enable IRQ in PIC
+	mov dx, 0x21
+	in al, dx
+	and al, ~(1 << irq)
+	out dx, al
+
+	; reset parser state
+	mov word [0x400+pstate], parse.start
+
+	call greet
+
+	pop ds
+	pop si
+	pop bx
+	pop dx
+	pop ax
+	retf
+
+greet   mov si, banner
+	xor bx, bx
+.loop   mov al, [cs:si]
+	test al, al
+	jz .exit
+	mov ah, 0x0e
+	int 0x10
+	inc si
+	jmp .loop
+.exit   ret
+
+putc	mov ah, al
+	; check if transmit buffer empty
+.l01	mov dx, lsr
+	in al, dx
+	test al, 0x20
+	jz .l01
+	mov al, ah
+	; send char to uart
+	mov dx, data
+	out dx, al
+	ret
+
+pdx:	; this double-call is essentially a 4 times repeating loop
+	call .l1
+.l1:	call .l2
+.l2:	; set up cl for bit shifts
+	mov cl, 4
+	; grab highest nibble from dx
+	mov al, dh
+	; remove highest nibble from dx
+	shl dx, cl
+	; shift away second-highest nibble that we accidentally copied
+	shr al, cl
+	; map 0-9 to ascii codes for '0' to '9'
+	add al, 0x30
+	; if result is larger than '9', ...
+	cmp al, 0x3a
+	jl pputc
+	; ... add 7 so we continue at 'A'
+	add al, 7
+pputc	mov ah, 0x0e
+	xor bx, bx
+	int 0x10
+	ret
+
+	; system bootstrap
+int19	sti
+	xor ax, ax
+	int 0x16
+	mov dx, ax
+	call pdx
+	mov al, 0x0A
+	call pputc
+	mov al, 0x0D
+	call pputc
+	jmp int19
+
+	; video services
+int10   cmp ah, 0x0e
+	jne .chain
+
+	push ax
+	push dx
+
+	call putc
+
+	pop dx
+	pop ax
+
+.chain  sub sp, 4
+	push bp
+	mov bp, sp
+	; stack: BP IP:CS IP:CS FL
+
+	push ax
+	push ds
+
+	xor ax, ax
+	mov ds, ax
+	; copy offset
+	mov ax, [4*0x47]
+	mov [bp+2], ax
+	; copy segment
+	mov ax, [4*0x47+2]
+	mov [bp+4], ax
+
+	pop ds
+	pop ax
+
+	pop bp
+	retf
+
+
+	; uart controller irq
+intu	push ax
+	push dx
+	; check if we controller has data ready
+	mov dx, isr
+	in al, dx
+	and al, 0xF
+	cmp al, 4
+	jne ugetc.ret
+	; set DS to bios data area
+	push bx
+	push ds
+	mov ax, 0x40
+	mov ds, ax
+	; receive data
+	mov dx, data
+	in al, dx
+	jmp near [pstate] ; load parser state
+ugetc	pop word [pstate] ; save parser state
+	pop ds
+	pop bx
+	; send non-specific EOI signal
+.ret	mov al, 0x20
+	out 0x20, al
+	pop dx
+	pop ax
+	iret
+
+	; parse loop
+	; this is called from inside the uart interrupt
+	; only call ugetc when nothing on stack, so no nested funcs
+parse	call ugetc
+.start	cmp al, 0x1B
+	je .esc
+	cmp al, 0x7F
+	je .bs
+.ascii	mov dl, al
+	mov bx, kmap
+	cs xlatb
+	mov dh, al
+	; insert key code into buffer in bios data area
+.insert	mov bx, [0x1C] ; get next empty slot
+	mov [bx], dx ; store key code
+	add bx, 2
+	cmp bx, 0x3E ; are we beyond last pos?
+	jc .nowrap
+	mov bx, 0x1E ; first position
+.nowrap	cmp bx, [0x1A] ; next to-read slot
+	je parse
+	mov [0x1C], bx ; commit if not full
+	jmp parse
+.bs	mov dx, 0x0E08
+	jmp .insert
+.esc	call ugetc
+	cmp al, 0x5B
+	je .csi
+	cmp al, 'O'
+	je .vt_o
+	jmp parse
+.csi	mov byte [parg], 0 ; reset argument
+.csicon	call ugetc
+	cmp al, 0x30
+	jc parse
+	cmp al, 0x3A
+	jnc .nonum
+	sub al, 0x30
+	mov dl, al
+	mov al, 0xA
+	mul byte [parg]
+	add al, dl
+	mov [parg], al
+	jmp .csicon
+.nonum	cmp al, '~'
+	jne .letter
+	mov al, [parg]
+	mov bx, fkeysn
+	jmp .lookup
+.vt_o	call ugetc ; VT100 \eO... sequences
+.letter	sub al, 0x40
+	mov bx, fkeysc
+.lookup	cs xlatb
+	cmp al, 0
+	je parse
+	mov dh, al
+	mov dl, 0
+	jmp .insert
+
+	align 128
+
+	; ascii -> XT scancode map
+	; this assumes US querty layout
+kmap	db 0x00,0x1E,0x30,0x2E, 0x20,0x12,0x21,0x22, 0x23,0x0F,0x24,0x25, 0x26,0x1C,0x31,0x18
+	db 0x19,0x10,0x13,0x1F, 0x14,0x16,0x2F,0x11, 0x2D,0x15,0x2C,0x01, 0x2B,0x1B,0x07,0x0C
+
+	db 0x39,0x02,0x03,0x04, 0x05,0x06,0x08,0x28, 0x0A,0x0B,0x09,0x0D, 0x33,0x0C,0x34,0x35
+	db 0x0B,0x02,0x03,0x04, 0x05,0x06,0x07,0x08, 0x09,0x0A,0x27,0x27, 0x33,0x0D,0x34,0x35
+
+	db 0x03,0x1E,0x30,0x2E, 0x20,0x12,0x21,0x22, 0x23,0x17,0x24,0x25, 0x26,0x32,0x31,0x18
+	db 0x19,0x10,0x13,0x1F, 0x14,0x16,0x2F,0x11, 0x2D,0x15,0x2C,0x1A, 0x2B,0x1B,0x07,0x0C
+
+	db 0x29,0x1E,0x30,0x2E, 0x20,0x12,0x21,0x22, 0x23,0x17,0x24,0x25, 0x26,0x32,0x31,0x18
+	db 0x19,0x10,0x13,0x1F, 0x14,0x16,0x2F,0x11, 0x2D,0x15,0x2C,0x1A, 0x2B,0x1B,0x29,0x70
+
+	; function keys by character
+	; \eO$c, looks up $c to XT scancode
+	; table is like ascii, except it starts at 0x40 '@'
+fkeysc	db 0,0x48,0x50,0x4D, 0x4B,0,0x4F,0, 0x47,0,0,0, 0,0,0,0
+	db 0x3B,0x3C,0x3D,0x3E, 0,0,0,0, 0,0,0,0, 0,0,0,0
+	db 0,0,0,0, 0,0,0,0, 0,0,0,0, 0x42,0,0,0
+	db 0,0,0,0, 0x3F,0x40,0x41,0x43, 0x44,0,0,0, 0,0,0,0
+
+	; function keys by numbers
+	; 10 entries per line
+	; \e[$n~, looks up $n to XT scancode
+fkeysn	db 0,0x47,0x52,0x53,0, 0x49,0x51,0x47,0x4F,0 ; 0-9
+	db 0,0x3B,0x3C,0x3D,0x3E, 0x3F,0,0x40,0x41,0x42 ; 10-19
+	db 0x43,0x44,0,0x85,0x86, 0,0,0,0,0 ; 20-29
+	db 0,0,0,0,0, 0,0,0,0,0 ; 30-39
+
+	align 512