code:devstart - ikarishinjieva/unixV6-code-analyze-chs GitHub Wiki

5087

5088 /* Device start routine for disks

5089  * and other devices that have the register

5090  * layout of the older DEC controllers (RF, RK, RP, TM)

5091  */

5092 #define IENABLE 0100

5093 #define WCOM 02

5094 #define RCOM 04

5095 #define GO 01

5096 devstart(bp, devloc, devblk, hbcom)

5097 struct buf *bp;

5098 int *devloc;

5099 {

5100      register int *dp;

5101      register struct buf *rbp;

5102      register int com;

• com为待传给寄存器RKCS的局部变量

5103

5104      dp = devloc;

• RKDA地址赋给dp
  • 则 dp-1 为RKBA地址, dp-2 为RKWC地址, dp-3 为RKCS地址,详见RK磁盘 寄存器

5105      rbp = bp;

5106      *dp = devblk; /* block address */

5107      *--dp = rbp->b_addr; /* buffer address */

5108      *--dp = rbp->b_wcount; /* word count */

• 将RKDA置为devblk
• 将RKBA置为b_addr
• 将RKWC置为b_wcount

5109      com = (hbcom<<8) | IENABLE | GO |

5110           ((rbp->b_xmem & 03) << 4);

• com置IENABLE,GO标志
• 将第4,5两位置为rbp->xmem的高2位,rbp->xmem的意义参见struct buf

5111      if (rbp->b_flags&B_READ)

5112           com =| RCOM;

• 如果为读,置RCOM标志

5113      else

5114           com =| WCOM;

• 如果为写,置WCOM标志

5115      *--dp = com;

• 将com赋值给RKCS

5116 }

5117 /* ------------------------- */

• code:rkstart