arch/um/drivers/slip_common.h

   1 #ifndef __UM_SLIP_COMMON_H
   2 #define __UM_SLIP_COMMON_H
   3
   4 #define BUF_SIZE 1500
   5  /* two bytes each for a (pathological) max packet of escaped chars +  *
   6   * terminating END char + initial END char                            */
   7 #define ENC_BUF_SIZE (2 * BUF_SIZE + 2)
   8
   9 /* SLIP protocol characters. */
  10 #define SLIP_END             0300       /* indicates end of frame       */
  11 #define SLIP_ESC             0333       /* indicates byte stuffing      */
  12 #define SLIP_ESC_END         0334       /* ESC ESC_END means END 'data' */
  13 #define SLIP_ESC_ESC         0335       /* ESC ESC_ESC means ESC 'data' */
  14
  15 static inline int slip_unesc(unsigned char c, unsigned char *buf, int *pos,
  16                              int *esc)
  17 {
  18         int ret;
  19
  20         switch(c){
  21         case SLIP_END:
  22                 *esc = 0;
  23                 ret=*pos;
  24                 *pos=0;
  25                 return(ret);
  26         case SLIP_ESC:
  27                 *esc = 1;
  28                 return(0);
  29         case SLIP_ESC_ESC:
  30                 if(*esc){
  31                         *esc = 0;
  32                         c = SLIP_ESC;
  33                 }
  34                 break;
  35         case SLIP_ESC_END:
  36                 if(*esc){
  37                         *esc = 0;
  38                         c = SLIP_END;
  39                 }
  40                 break;
  41         }
  42         buf[(*pos)++] = c;
  43         return(0);
  44 }
  45
  46 static inline int slip_esc(unsigned char *s, unsigned char *d, int len)
  47 {
  48         unsigned char *ptr = d;
  49         unsigned char c;
  50
  51         /*
  52          * Send an initial END character to flush out any
  53          * data that may have accumulated in the receiver
  54          * due to line noise.
  55          */
  56
  57         *ptr++ = SLIP_END;
  58
  59         /*
  60          * For each byte in the packet, send the appropriate
  61          * character sequence, according to the SLIP protocol.
  62          */
  63
  64         while (len-- > 0) {
  65                 switch(c = *s++) {
  66                 case SLIP_END:
  67                         *ptr++ = SLIP_ESC;
  68                         *ptr++ = SLIP_ESC_END;
  69                         break;
  70                 case SLIP_ESC:
  71                         *ptr++ = SLIP_ESC;
  72                         *ptr++ = SLIP_ESC_ESC;
  73                         break;
  74                 default:
  75                         *ptr++ = c;
  76                         break;
  77                 }
  78         }
  79         *ptr++ = SLIP_END;
  80         return (ptr - d);
  81 }
  82
  83 struct slip_proto {
  84         unsigned char ibuf[ENC_BUF_SIZE];
  85         unsigned char obuf[ENC_BUF_SIZE];
  86         int more; /* more data: do not read fd until ibuf has been drained */
  87         int pos;
  88         int esc;
  89 };
  90
  91 #define SLIP_PROTO_INIT { \
  92         .ibuf   = { '\0' }, \
  93         .obuf   = { '\0' }, \
  94         .more   = 0, \
  95         .pos    = 0, \
  96         .esc    = 0 \
  97 }
  98
  99 extern int slip_proto_read(int fd, void *buf, int len,
 100                            struct slip_proto *slip);
 101 extern int slip_proto_write(int fd, void *buf, int len,
 102                             struct slip_proto *slip);
 103
 104 #endif