OZ_Buff, buffers low level interface

CALL $004E

IN:
            IX = buffer access
                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

            L = reason call
 

Reason	Name	Function
$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

            A = value to put (if required)
            BC = timeout (if required)

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

Registers changed after return:
            Depends on reason code.

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.

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.

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

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

IN :
            IX buffer access

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

IN :
            IX buffer access

OUT:
            Fc=0, always.

Notes:

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

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