//  Template file with defines of peripheral registers
//  QtMips simulator https://github.com/cvut/QtMips/
//  developed by Karel Koci and Pavel Pisa.
//
//  template.S       - example file
//
//  (C) 2019 by Pavel Pisa
//      e-mail:   pisa@cmp.felk.cvut.cz
//      homepage: http://cmp.felk.cvut.cz/~pisa
//      work:     http://www.pikron.com/
//      license:  public domain

// Directives to make interresting windows visible
#pragma qtmips show terminal
#pragma qtmips show registers
#pragma qtmips show memory

.globl _start
.globl __start
.set noreorder
.ent _start

// Serial port/terminal registers
// There is mirror of this region at address 0xffff0000
// to match QtSpim and Mars emulators

.equ SERIAL_PORT_BASE,      0xffffc000 // base address of serial port region

.equ SERP_RX_ST_REG,        0xffffc000 // Receiver status register
.equ SERP_RX_ST_REG_o,          0x0000 // Offset of RX_ST_REG
.equ SERP_RX_ST_REG_READY_m,       0x1 // Data byte is ready to be read
.equ SERP_RX_ST_REG_IE_m,          0x2 // Enable Rx ready interrupt

.equ SERP_RX_DATA_REG,      0xffffc004 // Received data byte in 8 LSB bits
.equ SERP_RX_DATA_REG_o,        0x0004 // Offset of RX_DATA_REG

.equ SERP_TX_ST_REG,        0xffffc008 // Transmitter status register
.equ SERP_TX_ST_REG_o,          0x0008 // Offset of TX_ST_REG
.equ SERP_TX_ST_REG_READY_m,       0x1 // Transmitter can accept next byte
.equ SERP_TX_ST_REG_IE_m,          0x2 // Enable Tx ready interrupt

.equ SERP_TX_DATA_REG,      0xffffc00c // Write word to send 8 LSB bits to terminal
.equ SERP_TX_DATA_REG_o,        0x000c // Offset of TX_DATA_REG


// Memory mapped peripheral for dial knobs input,
// LED and RGB LEDs output designed to match
// MZ_APO education Zynq based board developed
// by Petr Porazil and Pavel Pisa at PiKRON.com company

.equ SPILED_REG_BASE        0xffffc100 // base of SPILED port region

.equ SPILED_REG_LED_LINE,   0xffffc104 // 32 bit word mapped as output
.equ SPILED_REG_LED_LINE_o,     0x0004 // Offset of the LED_LINE
.equ SPILED_REG_LED_RGB1,   0xffffc110 // RGB LED 1 color components
.equ SPILED_REG_LED_RGB1_o,     0x0010 // Offset of LED_RGB1
.equ SPILED_REG_LED_RGB2,   0xffffc114 // RGB LED 2 color components
.equ SPILED_REG_LED_RGB2_o,     0x0014 // Offset of LED_RGB2
.equ SPILED_REG_KNOBS_8BIT, 0xffffc124 // Three 8 bit knob values
.equ SPILED_REG_KNOBS_8BIT_o,   0x0024 // Offset of KNOBS_8BIT

// The simple 16-bit per pixel (RGB565) frame-buffer
// display size is 480 x 320 pixel
// Pixel format RGB565 expect
//   bits 11 .. 15 red component
//   bits  5 .. 10 green component
//   bits  0 ..  4 blue component
.equ LCD_FB_START,          0xffe00000
.equ LCD_FB_END,            0xffe4afff

// Mapping of interrupts
// Irq number   Cause/Status Bit   Source
//  2 / HW0      10                Serial port ready to accept character to Tx
//  3 / HW1      11                There is received character ready to be read
//  7 / HW5      15                Counter reached value in Compare register

// Original MIPS start address after reset
.org    0x80020000

.text

__start:
_start:

loop:	la	$a0, SERIAL_PORT_BASE  // load base address of serial port
	// it is pseodooperation lui $a0, 0xffff ; ori $a0, $a0, 0xc000
	// can be optimized as addi $a0, $zero, 0xffffc000-0x100000000
	// in this particular case

	la	$a1, text_1	// load address of text

next_char:lb	$t1, 0($a1)	// load one byte after another
	beq	$t1, $zero, end_char // is this the terminal zero byte
	addi	$a1, $a1, 1	// move pointer to next text byte
tx_busy:	lw	$t0, SERP_TX_ST_REG_o($a0) // read status of transmitter
	andi	$t0, $t0, SERP_TX_ST_REG_READY_m // mask ready bit
	beq	$t0, $zero, tx_busy	// if not ready wait for ready condition
	nop			// fill branch instruction delay slot
	sw	$t1,SERP_TX_DATA_REG_o($a0) // write byte to Tx data register
	beq       $zero, $zero, next_char // unconditional branch to process next byte
	nop			// fill delay slot

end_char:	break			// stop continuous execution
				// request developer interaction
	beq	$zero, $zero, loop
	nop			// fill delay slot

.end _start

.data

data_1:	.word	1, 2, 3, 4	// example how to fill data words

text_1:	.asciz	"Hello word.\n"	// store zero terminated ASCII text

// if whole source compile is OK the switch to core tab
#pragma qtmips tab core