Developper's Notes Addendum

BUFFERS MANAGEMENT

Introduction

As you know, OZ is very structured for i/o management. The different system buffers follow the same rule. They are basicly managed with a special OZ call ($004E).

1 - Buffer types

There are three different buffer types:

Name Access Description

KB $0216 the keyboard buffer

RX $0233 the recieve data buffer for the serial interface

TX $0229 the transmit data buffer for the serial interface

Name	Access	Description
KB	$0216	the keyboard buffer
RX	$0233	the recieve data buffer for the serial interface
TX	$0229	the transmit data buffer for the serial interface

The access links to a buffer frame placed in the OS RAM variables area. Each buffer frame is 8 bytes length.

Frame structure:

address length description

IX 2 associated handle (for the serial port)

-01 1 pointer for input

-02 1 pointer for output

-03 1 unused

-04 1 buffer high byte address

-05 1 buffer start address

-06 1 buffer end address

address	length	description
IX	2	associated handle (for the serial port)
-01	1	pointer for input
-02	1	pointer for output
-03	1	unused
-04	1	buffer high byte address
-05	1	buffer start address
-06	1	buffer end address

The buffer area begins at $0B00, just after the handles and ends at $0BFF.

address length description

0B00 32 KB buffer

0B20 96 TX buffer

0B80 128 RX buffer

address	length	description
0B00	32	KB buffer
0B20	96	TX buffer
0B80	128	RX buffer

2 - Buffer operation : OZ_BUFF routine

OZ works on these buffers with a special call placed in the system RAM. We will name it OZ_BUFF, called by the vector $004E (just before OZ_DI). Here is the call description :

OZ_BUFF, buffer interface

CALL $004E

IN:

IX buffer access
L reason call
Other register parameters depend on reason call

Reason call:

$00 BF_PB Write to buffer

$03 BF_GB Read from buffer

$06 BF_PBT Write to buffer with timeout

$09 BF_GBT Read from buffer with timeout

$0C BF_STA Get buffer status

$0F BF_PUR Purge buffer

Reason call:
$00	BF_PB	Write to buffer
$03	BF_GB	Read from buffer
$06	BF_PBT	Write to buffer with timeout
$09	BF_GBT	Read from buffer with timeout
$0C	BF_STA	Get buffer status
$0F	BF_PUR	Purge buffer

OUT:

Depends on reason code, see below.
IX always remains unchanged.

BF_PB (L = $00), Write byte to buffer

IN :
A value to put
IX buffer access

Out if call succeeded:
Fc=0, H full slots, L empty slots.

Out if call failed:
Fc=1, A=RC_EOF buffer is full.

BF_GB (L = $03), Read byte from buffer

IN : IX buffer access

Out if call succeeded:
Fc=0, A=C data , H full slots, L empty slots.

Out if call failed:
Fc=1, A=RC_EOF buffer is empty.

BF_PBT (L = $06), Write byte to buffer with timeout

IN :
A value to put
BC timeout, $FFFF for default
IX buffer access

Out if call succeeded:
Fc=0, BC remaining timeout

Out if call failed:
Fc=1, A=RC_SUSP, RC_ESC, RC_TIME

BF_GBT (L = $09), Read byte from buffer with timeout

IN :
BC timeout, $FFFF for default
IX buffer access

Out if call succeeded:
Fc=0, A data read, BC remaining timeout

Out if call failed:
Fc=1, A=RC_SUSP, RC_ESC, RC_TIME

BF_STA (L = $0C), Get buffer status

IN : IX buffer access

OUT: Fc=0, always.
H full slots (bytes in use)
L empty slots (free bytes)

BF_PUR (l = $0F), Purge buffer

IN : IX buffer access

OUT: Fc=0, always.

Thierry Peycru (Zlab), March 1998.