ArchitectureAssembler/18_InterruptsDMA

Ïðåðûâàíèÿ è DMA

1. Ïðåðûâàíèå ? ñèãíàë, ñîîáùàþùèé ïðîöåññîðó î íàñòóïëåíèè êàêîãî-ëèáî âíåøíåãî ñîáûòèÿ.
   • àñèíõðîííû
   • ïîçâîëÿþò îñâîáîäèòü cpu îò àêòèâíîãî îæèäàíèÿ.
2. Ïðîáëåìû âîçíèêàþùèå ïðè îáðàáîòêå ïðåðûâàíèé:
   • ðàñïîçíàâàíèå ïðèðîäû ïðåðûâàíèÿ
   • ïðåðûâàíèÿ âàæíû
   • ïðåðûâàíèÿ íóæíî áûñòðî îáðàáîòàòü
3. Ìàñêèðîâàíèå ïðåðûâàíèé.
   • Ïðåðûâàíèÿ, â çàâèñèìîñòè îò âîçìîæíîñòè çàïðåòà, äåëÿòñÿ íà:
     • ìàñêèðóåìûå ? ïðåðûâàíèÿ, êîòîðûå ìîæíî çàïðåùàòü óñòàíîâêîé ñîîòâåòñòâóþùèõ áèòîâ â ðåãèñòðå ìàñêèðîâàíèÿ ïðåðûâàíèé;
     • íåìàñêèðóåìûå ? îáðàáàòûâàþòñÿ âñåãäà, íåçàâèñèìî îò çàïðåòîâ íà äðóãèå ïðåðûâàíèÿ.
4. Ïðèîðèòåòû îáñëóæèâàíèÿ ïðåðûâàíèé.
5. Ïðåðûâàíèÿ â Mars.
   1. Ìèêðîïðîöåññîð èìååò âõîäû ïðåðûâàíèÿ.
   2. Êàæäûé çàïðîñ ïðåðûâàíèÿ ìîæåò èíäèâèäóàëüíî ìàñêèðîâàòüñÿ(âêëþ÷àþòñÿ ïðè 1) ñîîòâåòñòâóþùèìè ðàçðÿäàìè ïîëÿ Int Mask â ðåãèñòðå Status. Âñå çàïðîñû ïðåðûâàíèé ìàñêèðóþòñÿ ïðè óñòàíîâêå çíà÷åíèÿ áèòà IÅ=1 â ðåãèñòðà Status.

   3. Âñå ïðåðûâàíèÿ îáíàðóæèâàþòñÿ ïðîöåññîðîì. Ïðè ïîñòóïëåíèè ñèãíàëîâ ïðåðûâàíèÿ ïðîöåññîð ñáðàñûâàåò(0) áèòû ïîëÿ ExcCode ðåãèñòðà Cause. Ïðè ýòîì ñîäåðæèìîå ïîëÿ IP ðåãèñòðà Cause áóäåò ïîêàçûâàòü, íà êàêèå âõîäû ïîñòóïèëè ñèãíàëû ïðåðûâàíèÿ. Ïðè ïîñòóïëåíèè íåñêîëüêèõ çàïðîñîâ ïðåðûâàíèÿ ïðèîðèòåò èõ îáñëóæèâàíèÿ äîëæåí çàäàâàòüñÿ ïðîãðàììîé-îáðàáîò÷èêîì.

   4. Ñèãíàë ïðåðûâàíèÿ ïðîäîëæàåò âîñïðèíèìàòüñÿ ïðîöåññîðîì ïîñëå íà÷àëà îáðàáîòêè ïðåðûâàíèÿ. ×òîáû èçáåæàòü ïîâòîðíîãî îáñëóæèâàíèÿ çàïðîñà, ïðîãðàììà-îáðàáîò÷èê äîëæíà âûäàòü ñîîáùåíèå ñîîòâåòñòâóþùåìó âíåøíåìó óñòðîéñòâó íà ñíÿòèå çàïðîñà ïðåðûâàíèÿ èëè ïðîèçâåñòè ìàñêèðîâàíèå çàïðîñà ïóòåì ñáðîñà â 0 ñîîòâåòñòâóþùåãî áèòà IMx ðåãèñòðå Status.
6. Ïðèìåð:

      1 .text
      2         .globl main
      3 main:
      4         mfc0 $a0, $12                   # read from the status register
      5         ori $a0, 0xff11                 # enable all interrupts
      6         mtc0 $a0, $12                   # write back to the status register
      7 
      8         lui $t0, 0xFFFF                 # $t0 = 0xFFFF0000;
      9         ori $a0, $0, 2                          # enable keyboard interrupt
     10         sw $a0, 0($t0)                  # write back to 0xFFFF0000;
     11                 
     12 here: 
     13         j here                          # stay here forever
     14         nop
     15         li $v0, 10                              # exit,if it ever comes here
     16         syscall
     17 
     18 
     19 .ktext 0x80000180                               # kernel code starts here
     20         
     21         .set noat                               # tell the assembler not to use $at, not needed here actually, just to illustrae the use of the .set noat
     22         move $k1, $at                   # save $at. User prorams are not supposed to touch $k0 and $k1 
     23         .set at                         # tell the assembler okay to use $at
     24         
     25         sw $v0, s1                              # We need to use these registers
     26         sw $a0, s2                              # not using the stack because the interrupt might be triggered by a memory reference 
     27                                         # using a bad value of the stack pointer
     28 
     29         mfc0 $k0, $13                   # Cause register
     30         srl $a0, $k0, 2                         # Extract ExcCode Field
     31         andi $a0, $a0, 0x1f
     32 
     33     bne $a0, $zero, kdone                       # Exception Code 0 is I/O. Only processing I/O here
     34     nop
     35     
     36         lui $v0, 0xFFFF                 # $t0 = 0xFFFF0000;
     37         lw $a0, 4($v0)                  # get the input key
     38         li $v0,1                                # print it here. 
     39                                         # Note: interrupt routine should return very fast, so doing something like 
     40                                         # print is NOT a good practice, actually!
     41         syscall
     42 
     43         li $v0,4                                # print the new line
     44         la $a0, new_line
     45         syscall
     46 
     47 kdone:
     48         mtc0 $0, $13                            # Clear Cause register
     49         mfc0 $k0, $12                   # Set Status register
     50         andi $k0, 0xfffd                        # clear EXL bit
     51         ori  $k0, 0x01                          # Interrupts enabled
     52         mtc0 $k0, $12                   # write back to status
     53     
     54     lw $v0, s1                          # Restore other registers
     55         lw $a0, s2
     56 
     57         .set noat                               # tell the assembler not to use $at
     58         move $at, $k1                   # Restore $at
     59         .set at                                 # tell the assembler okay to use $at
     60 
     61         eret                                    # return to EPC
     62     nop
     63 
     64 .kdata                                  # kernel data
     65 s1:     .word 10
     66 s2:     .word 11
     67 new_line: 
     68         .asciiz "\n"
   

7. DMA - ïðÿìîé äîñòóï ê ïàìÿòè.