1 files changed, 98 insertions, 0 deletions
diff --git a/ebus-racket/ebus/layer2.rkt b/ebus-racket/ebus/layer2.rkt
new file mode 100644
index 0000000..f9bc31a
--- /dev/null
+++ b/ebus-racket/ebus/layer2.rkt
@@ -0,0 +1,98 @@
+#lang racket/base
+(require (only-in racket/bool false?)
+         "../3rdparty/bzlib/parseq/main.ss")
+
+(define-logger ebus2)
+
+(define ebus-const-syn #xaa) ;; SYN
+(define ebus-const-escape #xa9) ;; Escape-Sequence Start
+(define ebus-const-ackok #x00) ;; ACK
+(define ebus-const-broadcastaddr #xfe) ;; Broadcast Address
+
+(struct ebus-body-broadcast (crc) #:transparent)
+
+(struct ebus-body-mastermaster (crc) #:transparent)
+
+(struct ebus-body-masterslave
+  (crc payloadSlaveLength payloadSlave crcSlave)
+  #:transparent)
+
+(struct ebus-paket
+  (source destination primaryCommand secondaryCommand payloadLength payload body)
+  #:transparent)
+
+;; single, maybe escaped, payload data byte 
+(define ebus-payload
+  (choice (seq escape-seq <- ebus-const-escape
+               escape-code <- (byte-in (list 0 1))
+               (return (cond
+                         ((= escape-code 0) ebus-const-escape)
+                         ((= escape-code 1) bytes ebus-const-syn))))
+          any-byte
+          ))
+
+(define parse-ebus-broadcast
+  (token (seq crc <- any-byte
+              syn <- ebus-const-syn
+              (return (ebus-body-broadcast crc)))))
+
+(define parse-ebus-mastermaster
+  (token (seq  crc <- any-byte
+               ack <- ebus-const-ackok ;; ACK des Empfängers
+               syn <- ebus-const-syn   ;; SYN des Senders
+               (return (ebus-body-mastermaster crc)))))
+
+(define parse-ebus-masterslave 
+  (token (seq crc <- any-byte
+              ack <- ebus-const-ackok ;; ACK des Empfängers
+              payloadSlaveLength <- any-byte
+              payloadSlave <- (repeat ebus-payload payloadSlaveLength payloadSlaveLength)
+              crcSlave <- any-byte
+              ackSlave <- ebus-const-ackok ;; ACK des Senders
+              synSlave <- ebus-const-syn   ;; SYN des Senders
+              (return (ebus-body-masterslave crc payloadSlaveLength payloadSlave crcSlave)))))
+
+(define parse-ebus-paket
+  (token (seq source <- any-byte
+              destination <- any-byte
+              primaryCommand <- any-byte
+              secondaryCommand <- any-byte
+              payloadLength <- any-byte
+              payload <- (repeat ebus-payload payloadLength payloadLength)
+              body <- (cond ((= destination ebus-const-broadcastaddr) parse-ebus-broadcast)
+                            (else (choice parse-ebus-mastermaster 
+                                          parse-ebus-masterslave)))
+              (return (ebus-paket source 
+                                  destination
+                                  primaryCommand
+                                  secondaryCommand
+                                  payloadLength
+                                  payload 
+                                  body)))))
+
+(define ebus-sync (tokens syncs <- (seq (repeat (string->bytes/latin-1 "\xaa")))
+                          (return (length syncs))))
+
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(define (read-ebus input-port)
+  (define syn   ((make-reader ebus-sync #:sof? #f #:eof? #f)  input-port))
+  (define paket   ((make-reader parse-ebus-paket #:sof? #f #:eof? #f) input-port))
+  (cond ((not (false? syn)) (log-ebus2-debug "dropped ~a x SYN (~a)" syn ebus-const-syn)))
+  (cond ((not (false? paket)) paket)
+        ((eof-object? (peek-byte input-port)) eof)
+        (else
+         ;; skip one byte
+         (let ([byte (read-byte input-port)])
+           (log-ebus2-debug "drop ~s 0x~x" byte byte))
+         (read-ebus input-port))))
+
+(provide 
+ ;; Read Layer Ebus-Paket `ebus-paket`
+ read-ebus
+ ;; Expose datastructures
+ (struct-out ebus-paket)
+ (struct-out ebus-body-broadcast)
+ (struct-out ebus-body-mastermaster)
+ (struct-out ebus-body-masterslave))