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>a1 INTRODUCTION
The ALC program works as a simulated HDLC driver for the PAXNET system.
That is the reason why this manual is written as a collection of
modi_fica_tion to the "RC3502 COM201 HDLC DRIVER, Reference Manuals".

>a2 ALC Protocol
The protocol is a packet switching data trans_mission, full duplex,
running on a asynchronous transmission line. See AL.RC.20 and
AL.RC.22.

>a2 Driver Structure
The program main loop is composed of two parts: one for handling
requests (this part is a close copy of the HDLC driver) and one for
handling the LAM-driver commu_nication.

>a2 Line States
As in HDLC.

>a2 Driver Functions
Transput messages are executed with a maximum data stack depth of
1 only.

>a2 Modem Signal Consideration
ALC uses LAM108 or LAM116, so V.24 is used instead of X.25.

>a2 Testoutput
As in HDLC. This function has never been tested.

>a1 DRIVER INTERFACE
>a2 Driver Process Creation
The process name (used in LINK call) is 
 
 alc

The process incar_na_tion must be created with the follo_wing
parameters:
>hc
>tc $
     
  (req_sem:!ts_pointer;
   lam_sem:!sempointer;
   port:byte)

reg_sem is the semaphore to which all messages to the driver
should be signalled.
>hc _

TYPE

>hc
 ts_pointer = record
              s:sempointer;
              w:sempointer;
              end;

lam_sem is the LAM driver main semaphore. port is the LAM port used.
The range is 0 - 15.
>hc _

Stack size 400 words.

A coroutine priority is recommended.

>a2 Driver Messages
In answers, U3 is set to port.

>a3 Control Messages
>a4 Sense Status Message
As in HDLC.

SQD and CI are always 0.

>a4 Connect Message
Connect ident is not used.

K is not used. A K = 1 is performed.

>a4 Disconnect Messge
As in HDLC.

>a4 Return All Buffers Message
>ul
Function:

The line state is set to disconnect. 
All unused buffers are returned. The return-all-buffers message
is returned with result = ok.

Buffers located at the LAM driver are returned, when they arrive 
from the LAM driver.

>a4 Return Unused Buffers Message
As in HDLC.

>a4 Modem Control Message
No function.

>a4 Read Statistics Message
Same function as in HDLC. Same data buffer size as in HDLC.
The meaning of the counters is changed.

Data buffer from driver:

Record

 na1, na2, na3,
 na4, received,
 na6, transmitted,
 na8, skipped,
 na10, retransmitted,
>hc
 last_receiver_error,
 last_trans_error,
 timer_after_enq,
 wait_for_trans,
 timer_after_data,
 dsr,
 dcd,
 na19,
 last_lam_status,
 last_opcodes,
 trans_errors,
 rec_errors:integer;
 fut_use:array (1..6) of integer

end;
>hc _

Most counters are selfexplanatory. Others are described here:

>hc
    
 na_counter are always 0.
 last_receiver_error is U4 * 256 + U2 from LAM.

 last_trans_error is same format.
 wait_for_trans s no of times on receipt has
 been quequed while transmitter was engaged
 (with block transfer).

 dsr is no of times DSR signal was off.
 dcd is no of times DCD signal was off.

 last_lam_status is U4 * 256 + U2 from LAM.
 last_opcodes is last received opcode * 256
 + last trans. opcode.

 fut_use  if LAM answer U2 is > 8
 then fut_use (U2 div 8) is incremented.

>hc _
All counters are non-negative counters,
counting cyclically in the range 0 - 32767.

>a4 Read and Clear Statistics Message
As in HDLC.

>a4 Sense Line Speed Message
As in HDLC. ALC is running 1200 bps.

>a4  Event Message
As in HDLC. Event numbers are

 0  : line state becomes connected
 1  : line state requested disconnected
 2  : not used
 3  : no answer from LAM after datablocks
 4  : no answer from LAM after control blocks
 5  : unknown answer from LAM
 6  : not used
 7  : illegal opcode. Line state still connected
 8  : not used
 9  : modem off or cable off
 10 : no answer from LAM
 11 : timeout or too many retries,
      linestate is connecting
 12 : too many retries, linestate is
      disconnected
 13 : LAM receives errors
 14 : LAM transmit errors
 15 : ALC process in exception

 3, 4, 10 indicate LAM driver problems.

>a4  Testoutput Message
As in HDLC, never tested.

>a3 Transput Messages
As in HDLC.

>a2 Testoutput Formats
As in HDLC, not used yet.

>a1 PERFORMANCE
Depends highly on the LAM driver.

>a1 REFERENCES
>tb 5 (1)
CCITT Draft Revised Recommendation X.25. Computer Communication
Review, vol. 10, No. 1 and 2.

>tb 5 (2) 
Konventioner for drivere til NY og LAMBDA. UDV-NYSK[RM.EL.68 (Danish).

>tb 5 (3)
Konventioner for PASCAL80 driver interfacer. UDV-PASCAL80.EL.1 (Danish).

>tb 5 (4)
Addendum til konversioner for PASCAL80 driver interfaces. UDV-PASCAL80.HLV.12
(Danish).

>tb 5 (5)
RC3502 COM201 HDLC driver. Reference Manual. RCSL43-AA699 HLV.

>tb 5 (6)
Protokol for fuld duplex tilslutning af vagtcentraler. 
AL.RC.20.OER (Danish).

>tb 5 (7)
Tilslutning af vagtcentraler. AL.RC.22.OER (Danish).
«eof»
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