Z88 Developers' Notes
Contents   Contents of System Calls

OS_Sr, save & restore operations

RST 20H, DEFB $6C

IN: 

     A = reason code:
     SR_SUS ($01)   Save user screen
     SR_WPD ($03)   Write parameter data (mailbox)
     SR_RPD ($04)   Read parameter data (mailbox)
     SR_FUS ($05)   Free user screen
     SR_CRM ($06)   Remove card (not implemented)
     SR_CIN ($07)   Insert card (not implemented)
     SR_PWT ($08)   Page wait
     SR_RND ($09)   Occasionally a random number (system use)

     BC, DE, HL, IX = arguments
OUT, if call successful: 
     Fc = 0
     returned values depend on A(in)
OUT, if call failed: 
     Fc = 1
     A = error code:
          RC_UNK ($03), unknown request
          RC_BAD ($04), bad arguments
          RC_HAND ($08), bad handle
          RC_ROOM ($07), no room
          RC_ESC ($01), with SR_PWT
          RC_SUSP ($69), with SR_PWT
          RC_DRAW ($66), with SR_PWT
          RC_QUIT ($67), with SR_PWT
SR_SUS (A = $01), save user screen

IN: 

     -
OUT, if call succeeded: 
     Fc = 0
     IX = handle of saved screen
OUT, if call failed: 
     Fc = 1
     A = return code:
          RC_HAND ($08), not sufficiently room for screen in memory.
Registers changed after return: 
     A.BCDEHL/..IY same
     .F....../IX.. different
SR_RUS (A = $02), restore user screen

IN: 

     IX = handle of previously saved screen image
OUT, if call succeeded: 
     Fc = 0
     IX = 0
OUT, if call failed: 
     Fc = 1
     A = return code:
          RC_HAND ($08), screen handle was not valid
Registers changed after return: 
     A.BCDEHL/..IY same
     .F....../IX.. different
SR_FUS (A = $05), free user screen (not restoring screen image)

IN: 

     IX = handle of previously saved screen image
OUT, if call succeeded: 
     Fc = 0
     IX = 0
OUT, if call failed: 
     Fc = 1
     A = return code:
          RC_HAND ($08), screen handle was not valid
Registers changed after return: 
     A.BCDEHL/..IY same
     .F....../IX.. different
SR_PWT (A = $08), page wait

IN: 

     -
OUT, if call succeeded: 
     Fc = 0
     A = <BACKSPACE> ($08)
OUT, if call failed: 
     Fc = 1
     A = return code:
          RC_ESC ($01), escape condition detected
          RC_SUSP ($69), process suspended or machine revived
          RC_DRAW ($66), process suspended or screen corrupted
          RC_QUIT ($67), KILL request
Registers changed after return: 
     ..BCDEHL/IXIY same
     AF....../.... different
Notes:
Although an OS_In alike call is made that returns the proper return codes on pre-emption error codes, successful keyboard output is always <BACKSPACE>.

SR_RND (A = $09), random number

IN:

     -

Out:

     DEBC = random number

Notes:

The return value (random number) only changes when certain
operating system functions occur in between calls to OS_Sr. Repeated fetching
a random number may well result in the same value being returned!





SR_WPD ($03)   Write parameter data (mailbox)



IN:

     DE = name of information type (null-terminated)
     DE = 0, clear mailbox
     BHL = extended pointer to information
     C = length of information

OUT:

     Fc = 0, successfull

Registers changed after return:

     A.BCDEHL/IXIY same
     .F....../.... different

Notes:

Mailboxing functionality is explained in detail in "Application
Static Structures".

 

SR_RPD ($04)   Read parameter data (mailbox)

IN:

     DE = name of information type (null-terminated)
     BHL = extended pointer to buffer for information read
     C = maximum size of buffer

OUT, if call successful:

     Fc = 0
     C = actual data size

OUT, if call failed:

     Fc = 0
     A = return code
          RC_FAIL ($16), information type is not present

Registers changed after return:

     A.B.DEHL/IXIY same
     .F.C..../.... different

Notes:

Mailboxing functionality is explained in detail in "Application
Static Structures".