9. Technické a organizační prostředky (vnější události, výjimky, reálný čas)

Program irq_test.S pro společnou obsluhu sériového portu a časovače
// Directives to make interresting windows visible
#pragma qtmips show terminal
#pragma qtmips show registers
#pragma qtmips show cop0dock
#pragma qtmips show peripherals

.set SERIAL_PORT_BASE,     0xffffc000

.set SERP_RX_ST_REG_o,           0x00
.set SERP_RX_ST_REG_READY_m,      0x1
.set SERP_RX_ST_REG_IE_m,         0x2

.set SERP_RX_DATA_REG_o,         0x04

.set SERP_TX_ST_REG_o,           0x08
.set SERP_TX_ST_REG_READY_m,      0x1
.set SERP_TX_ST_REG_IE_m,         0x2

.set SERP_TX_DATA_REG_o,         0x0c

.set FREQ_FAST,  	           0x0800
.set FREQ_SLOW,		 0x2000

.set SLOW_CMD,   0x736c6f77
.set FAST_CMD,   0x66617374

.globl _start
.set noat
.set noreorder
.ent _start

.text

_start: 
   la    $t0, irq_entry - 0x180
   mtc0  $t0, $15, 1  // set EBase
   mfc0  $t1, $9, 0
   addi  $t1, $0, 50 
   mtc0  $t1, $11, 0
   la    $t0, next_counter
   sw    $t1, 0($t0)
   li    $21, SERIAL_PORT_BASE
   li    $20, SERP_RX_ST_REG_IE_m
   sw    $20, SERP_RX_ST_REG_o($21)
   li    $20, 0x00008801
   mtc0  $20, $12, 0  // set - status
loop:	
   la    $8, rd_ptr
   lw    $9, 0($8)
   lw    $10, 4($8)
   beq   $9, $10, no_new_char
   nop
   addi  $10, $9, 1
   andi  $10, $10, 0x3f
   sw    $10, 0($8)    
   add   $8, $9, $8
   lbu   $9, 8($8)
   la    $8, received_cmd
   lw    $10, 0($8)
   sll   $10, $10, 8
   or    $10, $10, $9
   sw    $10, 0($8)
   li    $11, FAST_CMD
   bne   $10, $11, not_fast
   nop
   la    $8, frequency
   addi  $9, $0, FREQ_FAST
   sw    $9, 0($8)	
   j     no_new_char
   nop          
not_fast:
   li    $11, SLOW_CMD
   bne   $10, $11, no_new_char
   nop
   la    $8, frequency
   addi  $9, $0, FREQ_SLOW
   sw    $9, 0($8)	
no_new_char:
   lui $8,0xffff
   ori $8,$8,0xc110 
   lw  $9,0x14($8)
   sw  $9,0($8)
   j loop
   nop


irq_entry:
   la    $26, save_regs
   sw    $8, 0($26)
   sw    $9, 4($26)
   sw    $10, 8($26)
   sw    $11, 12($26)
   mfc0  $26, $13, 0  // Cause
   andi  $27, $26, 0x00000800
   bne   $27, $0, rs232_rx_irq
   nop
test_timer:
   andi  $27, $26, 0x00008000
   bne   $27, $0, timer_irq
   nop
irq_end:
   la    $26, save_regs
   lw    $8, 0($26)
   lw    $9, 4($26)
   lw    $10, 8($26)
   lw    $11, 12($26)
   eret


rs232_rx_irq:
   li    $8, SERIAL_PORT_BASE
   lw    $9,0($8)
   andi  $9,$9,1
   beq   $9,$0, test_timer
   nop
read_next_char:
   la    $8, rd_ptr
   lw    $10, 4($8)
   addi  $9, $10, 1
   andi  $9, $9, 0x3f
   sw    $9, 4($8)
   lw    $11, 0($8)
   bne   $9, $11, free_buffer
   nop
   addi  $11, $11, 1
   andi  $11, $11, 0x3f
   sw    $11, 0($8)
free_buffer:
   add   $8, $8, $10
   li    $10, SERIAL_PORT_BASE
   lw    $9, SERP_RX_DATA_REG_o($10)
   sb    $9, 8($8)    //131     
   lw    $9,0($10)
   andi  $9,$9,1
   bne   $9,$0, read_next_char
   nop
   j     test_timer
   nop

timer_irq:
   la    $8, next_counter
   lw    $9, 0($8)
   lw    $10, 8($8)  //frequency
   add   $9, $9, $10
   sw    $9, 0($8)
   mtc0  $9, $11, 0
   lw    $9, 4($8)
   xori  $9, $9, 1
   sw    $9, 4($8)
   add   $10, $0, $0
   beq   $9, $0, turn_off
   nop
   addi  $10, $0, 0xff
turn_off:
   la    $8, 0xffffc110 
   sw    $10,4($8)
   j     irq_end 
   nop	

.data
.org   0x40000
received_cmd:
   .word 0
rd_ptr:
   .word 0
wr_ptr:
   .word 0
buffer:
   .word 0,0,0,0,0,0,0,0
   .word 0,0,0,0,0,0,0,0
save_regs:
   .word 0,0,0,0,0,0,0,0
   .word 0,0,0,0,0,0,0,0
next_counter:
   .word 0
turn_on:	
   .word 0
frequency:
   .word FREQ_FAST