How to emulate the Dobbertin HD20?
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The Dobbertin HD20 occupies only 5 I/O port addresses.
It's emulation is (compared to other devices) relatively simple.
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= Physical Properties =
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Sectors: 17 (0-16) on each track
Heads..: 4 (0-3)
Tracks.: 614 (0-613)
0-611 for data
612 is reserved
613 for parking the heads
=======> However, it would be great to provide 1024 tracks (0-1023) to have some more space
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= Ports =
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&FBE0: Data port (hddata) / Only 3 ports need to be emulated
&FBE1: Status register (hdstat) /
&FBE2: Select / configuration (hdslct) /
&FBE3: DMA / interrupt (hdmask) / These two ports can be ignored
&FBE4: Reset (hd_res) /
For the emulation ports &FBE0-2 (three ports only) are sufficient!
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= &FBE0: Data port =
====================
This port has four functions:
1. Send command bytes to this port
2. Send data to this port
3. Receive data from this port
4. Receive result bytes from this port
When sending / reiceiving data the CPC can send / receive 512 bytes at once.
It's not needed to wait, because the controller is very quick.
&FBE1: Status register
======================
This I/O address can be read to assess the status of the HD20 hard disc.
The significant bits are:
- Bit 0: If bit 0 is 0 then you need to wait for the HD20 / Ready bit
If bit 0 is 1 then the HD20 is ready to be used /
- Bit 1: If bit 1 is 0 then the HD20 does provide data / data flowing from controller to host ############# stimmt das ???
If bit 1 is 1 then the HD20 does expect data /#################################################### oder anders rum?
- Bit 2: If bit 2 is 0 then the HD20 is NOT in command state
If bit 2 is 1 then the HD20 is in command state
- Bit 3: If bit 3 is 0 then the controller is NOT selected - Error!!! / Controller selected bit
If bit 3 is 1 then the controller is selected and can be used /
If the input from &FBE1 is %xxxx1101 (binary) then the controller is in command state
and waits to receive command bytes
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= &FBE2: Select / configuration =
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This port is used to select the hard disc HD20, subsequently an command can be sent.
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= &FBE3: DMA / interrupt = - probable it's not necessary to emualate this port
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This port is used to set the operation mode only.
Example: (this is done when XDDOS gets initialized)
LD BC,&FBE3 ;BC = &FBE3 (DMA / Interrupts port)
LD A,&00
OUT (C),A ;send &00 to DMA/interrupt port
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= &FBE4: Reset = - probable it's not necessary to emualate this port
================ -------------------------------------------------
This port performs a reset of the HD20 just by writing a byte to it.
The content of the byte doesn't matter.
Read a sector
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Write a sector
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Additonal information
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The following information was obtained from Linux/drivers/block/xd.h and MESS pc_hdc.c.
Commands for HDC (incomplete list):
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CMD_TESTREADY &00 test drive ready
CMD_RECALIBRATE &01 recalibrate drive
??? &02 Request Syndrome
CMD_SENSE &03 request sense
CMD_FORMATDRV &04 format drive
CMD_VERIFY &05 read verify
CMD_FORMATTRK &06 format track
CMD_FORMATBAD &07 format bad track
CMD_READ &08 read
??? &09 Write Protect Sector
CMD_WRITE &0A write
CMD_SEEK &0B seek
Kommandos &0C bis &1B können in Datei sasi_r0a.pdf nachgelesen werden! Siehe dort!
Status (obtained when reading status register):
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STAT_READY &01 controller is ready
STAT_INPUT &02 data flowing from controller to host
STAT_COMMAND &04 controller in command phase
STAT_SELECT &08 controller is selected
STAT_REQUEST &10 controller requesting data
STAT_INTERRUPT &20 controller requesting interrupt
I/O Ports Lesen Schreiben
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&FBE0 Dobbertin Harddisc Data Port
&FBE1 Dobbertin Harddisc Status, Reset ---------------------> Lesen &00, &06 (Normalbetrieb an, an & gelesen)
&FBE2 Dobbertin Harddisc Select, Configuration -------------> Lesen &01 (wenn eingeschalten)
&FBE3 Dobbertin Harddisc DMA, Interrupt
&FBE4 Dobbertin Harddisc Reset
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= Example Codes =
=================
;Wait until the HD20 is ready
LD BC,&FBE1 ;HDSTAT -> 'BC'
wtctrl IN A,(C) ;Controller Status -> 'A'
AND 00001111B ;Mask significant Bits
BIT 0,A ;Controller Ready ?
RET NZ ;Yes, then RET
BIT 3,A ;Controller selected ?
JR NZ,wtctrl ;Yes, then wait
RET ;Else you should check for errors
;Check for errors
; ------ >>> ERROR CHECKING <<< ------
;
; RET mit CARRY = 1 und ZERO = 1 => No error
; RET mit CARRY = 0 und ZERO = 0 => error
LD BC,&FBE1 ;HDSTAT -> 'BC' = &FBE1
IN A,(C) ;Controller Status -> 'A'
AND 00001111B ;Mask significant Bits
errchck CP 00001111B ;STATUS State ?
JR NZ,hderror ;No, then jump to indicate error
DEC C ;HDDATA -> 'BC' = &FBE0
IN A,(C) ;Read Result-Phase byte -> 'A'
BIT 1,A ;Error occured ?
SCF ;No, then RET with
RET Z ; Carry & Zero = 1
;
hderror LD A,0FFH
AND A ;RET with Carry & Zero = 0
RET ; if an error occured
;SEND COMMAND
LD HL,command
sendcmd LD BC,&FBE2 ;HD20 select (hdslct)
OUT (C),A ;Select Controller
DEC C
DEC C ;HDDATA -> 'BC'
cmdloop INC C ;BC = &FBE1 (HDSTAT -> 'BC')
CALL wtctrl ;Wait Controller Ready (for 'wtcrtl' see before)
CP 00001101B ;COMMAND State ?
RET NZ ;No, then RET
DEC C ;BC = &FBE0 (HDDATA -> 'BC')
LD A,(HL) ;Command-Byte -> 'A'
OUT (C),A ;Zum Controller senden
INC HL
JR cmdloop
command is either hdrdsec or hdwrsec
For read / write:
hdrdsec DEFB 08H, xxH,yyH,zzH, 01H,02H ;Read Sector
hdwrsec DEFB 0AH, xxH,yyH,zzH, 01H,01H ;Write Sector
xx, yy, zz are defined as follows:
xx = HL + 1 = Head in bits 1,0 - Head can be 0-3
yy = HL + 2 = MSB Cyl. + Sector / Cylinder (high bits) in bits 7,6 / sector in bits 5,4,3,2,1 - Sector can be 0-16
zz = HL + 3 = LSB Cyl. / Cyliner (low bits) - Cylinder low bits can be 0-255
The hard disc has 614 tracks (from 0 to 613).
Tracks 0-612 are data (while track 613 is used for parking the four heads).
;Reset the hard disc and select configuration
;
LD BC,&FBE4 ;Reset Port
OUT (C),A ;send one byte to reset (content doesn't matter)
LD A,&32 ;50 ms waiting time
CALL &C964 ;Wait 1x 50 ms, preserve all registers
DEC C ;BC = &FBE3 (DMA / Interrupts)
LD A,&00
OUT (C),A ;send &00 to DMA/interrupt port
DEC C ;BC = &FBE2 (Select / Configuration)
IN A,(C) ;read status
CP &01 ;compare to 1
RET ;and returen