;* bootROM, a very small bootloader for $NAME
;*
;* protocol details:
;* abbrv: H = Host, CPU = C
;*
;* value/cmd              | direction | comment
;* ------------------------------------------------------------
;* 'H'                    | H -> C    | enter bootROM ("HI")
;* 'O'                    | C -> H    | ack bootROM entry ("OH HAI")
;*
;* 'W'0xZZZZZZZZ0xYYYYYYYY| H -> C    | write instr (0xYY...Y) to
;*                                    | address (0xZZ...Z)
;* 'D'                    | C -> H    | instr write done
;*
;* 'R'0xZZZZZZZZ          | H -> C    | read instr from address (0xZZ..Z)
;* 'F'0xYYYYYYYY          | C -> H    | instr read done and return instr
;*
;* 'Q'0xZZZZZZZZ0xYYYYYYYY| H -> C    | write data (0xYY...Y) to
;*                                    | address (0xZZ...Z)
;* 'A'                    | C -> H    | data write done
;*
;* 'T'0xZZZZZZZZ          | H -> C    | read data from address (0xZZ..Z)
;* 'G'0xYYYYYYYY          | C -> H    | read done and return data
;*
;* 'J'0xZZZZZZZZ          | H -> C    | jump to address (0xZZ...Z)
;*/
	.data

	.text
	.define UART_BASE, 0x2000
	.define UART_STATUS, 0x0
	.define UART_RECV, 0xc
	.define UART_TRANS, 0x8

	.define UART_TRANS_EMPTY, 0x1
	.define UART_RECV_NEW, 0x2

	.define PBASE, 0x2030
	.define PADDR, 0x4
	.define PDATA, 0x8

;-----
start:
	br+ main
	br+ main
	ret

main:
	ldi r10, UART_BASE@lo
	ldih r10, UART_BASE@hi
	ldi r11, PBASE@lo
	ldih r11, PBASE@hi
poll:
	call recv_byte
	; we received the enter bootrom sign
	xor r1, r1, r1
	cmpi r0, 0x48 ; 'H'
	breq+ bt_H
	br poll ; else

;-----
send_byte:
	ldw r3, UART_STATUS(r10)
	andx r3, UART_TRANS_EMPTY
	brnz+ send_byte ; branch if not zero
	stw r1, UART_TRANS(r10)
	ret

;-----
send_word:
	lrs r0, r1, 0
	call send_byte
	lrs r0, r1, 8
	call send_byte
	lrs r0, r1, 16
	call send_byte
	lrs r0, r1, 24
	call send_byte
	ret

;-----
recv_byte:
	ldw r3, UART_STATUS(r10)
	andx r3, UART_RECV_NEW
	brzs+ recv_byte; branch if zero
	xor r0, r0, r0
	ldw r0, UART_RECV(r10)
	ret

;-----
recv_word:
	xor r1, r1, r1
	call recv_byte
	or r1, r0, r1

	call recv_byte
	lls r1, r1, 8
	or r1, r0, r1

	call recv_byte
	lls r1, r1, 8
	or r1, r0, r1

	call recv_byte
	lls r1, r1, 8
	or r0, r0, r1
	xor r1, r1, r1

	ret

;-----
bootrom:
	call recv_byte
	xor r1, r1, r1

	cmpi r0, 0x57 ; 'W'
	breq- bt_W

	;cmpi r0, 0x52 ; 'R'
	;breq- bt_R

	cmpi r0, 0x51 ; 'Q'
	breq- bt_Q

	cmpi r0, 0x54 ; 'T'
	breq- bt_T

	cmpi r0, 0x4a ; 'J'
	breq- bt_J

	; cmpi r0, 0x48 ; 'H'
	; breq bt_H
	; FALL THROUGH ;)

bt_H:
	ldi r1, 0x4f ; 'O'
	call send_byte
	br bootrom

bt_W:
	ldi r1, 0x57 ; 'W'
	call send_byte
	call recv_word ; receive addr
	stw r0, PADDR(r11)
	call recv_word ; receive instr
	stw r0, PDATA(r11)
	ldi r1, 0x44 ; 'D'
	call send_byte
	br bootrom

;bt_R: ;lesen von IRAM wird nicht unterstuetzt
	;call recv_word ; receive addr
	;mov r2, r0
	;ldi r1, 0x46 ; 'F'
	;call send_byte
	;ldx r1, 0(r2)
	;call send_word
	;br bootrom

bt_Q:
	ldi r1, 0x51 ; 'Q'
	call send_byte
	call recv_word ; receive addr
	addi r6, r0, 0
	call recv_word ; receive data
	stw r0, 0(r6)
	ldi r1, 0x41 ; 'A'
	call send_byte
	br bootrom

bt_T:
	call recv_word ; receive addr
	mov r2, r0
	ldi r1, 0x47 ; 'G'
	call send_byte
	ldw r1, 0(r2)
	call send_word
	br bootrom

bt_J:
	; 'overflow' ROM