Difference between revisions of "RL8-A disk controller"

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(Fairly complete)
 
(Add bootstrap)
 
Line 93: Line 93:
 
  HS - Head Select
 
  HS - Head Select
 
  CYL - Cylinder
 
  CYL - Cylinder
 
 
===Command Register B===
 
===Command Register B===
  
Line 135: Line 134:
 
  DE - Drive Error ('Get Status' will provide details)
 
  DE - Drive Error ('Get Status' will provide details)
 
  DRDY - Drive  Ready
 
  DRDY - Drive  Ready
 
 
===Silo Buffer Register===
 
===Silo Buffer Register===
  
Line 152: Line 150:
 
| colspan=4 | Unused || DT || HS || CO || HO || BH || colspan=3 | STATE
 
| colspan=4 | Unused || DT || HS || CO || HO || BH || colspan=3 | STATE
 
{{12bitoctal-bitout}}
 
{{12bitoctal-bitout}}
 +
DT - Drive Type
 +
HS - Head Select
 +
CO - Cover Open
 +
HO - Heads Out
 +
BH - Brush Home
  
 
{| class="wikitable"
 
{| class="wikitable"
Line 186: Line 189:
 
  DSE - Drive Select Error
 
  DSE - Drive Select Error
  
<!-- ==Bootstraps==
+
==Bootstraps==
 
 
This [[bootstrap]] (which is position-independent [[object code]], so it can be placed anywhere; 04000 is good) will load the block at sector 0 of cylinder 0 of drive 0 into [[main memory]] at [[address]] 0:
 
  
 +
<!--This [[bootstrap]] will load the block at sector 0 of cylinder 0 of drive 0 into [[main memory]] at [[address]] 20: -->
 
{| border=1  
 
{| border=1  
! Address !! Data !! Mnemonic !! Description
+
! Address !! Data !! Comments
 
|- style="background-color: #ccccdd;"
 
|- style="background-color: #ccccdd;"
|1000||012700||MOV #174400,R0          ||Move the address of the Control Status register into R0
+
|21||7600|| Clear accumulator
 
|- style="background-color: #ccccff;"
 
|- style="background-color: #ccccff;"
|1002||174400||                         || (constant)
+
|22||6600|| Clear controller
 
|- style="background-color: #ccccdd;"
 
|- style="background-color: #ccccdd;"
|1004||012760||MOV #177400,6(R0)        ||Move block size (negative) into Multipurpose register
+
|23||7332|| Generate constant
 
|- style="background-color: #ccccff;"
 
|- style="background-color: #ccccff;"
|1006||177400||                         || (constant)
+
|24||6605|| Load SA with 20
 +
|- style="background-color: #ccccdd;"
 +
|25||1021|| Load constant into accumulator
 
|- style="background-color: #ccccff;"
 
|- style="background-color: #ccccff;"
|1010||000006||                         || (constant)
+
|26||6607|| Load WC
 
|- style="background-color: #ccccdd;"
 
|- style="background-color: #ccccdd;"
|1012||012710||MOV #14,@R0              ||Move 'Read Go' command into CSR
+
|27||2327|| Generate constant
 
|- style="background-color: #ccccff;"
 
|- style="background-color: #ccccff;"
|1014||000014||                         || (constant)
+
|30||6604|| Load CMD B
 
|- style="background-color: #ccccdd;"
 
|- style="background-color: #ccccdd;"
|1016||105710||TSTB (R0)                ||Test for 'Done' bit in CSR
+
|31||6601||Skip on done
 
|- style="background-color: #ccccff;"
 
|- style="background-color: #ccccff;"
|1020||100376||BPL 1016                ||Jump backward if not set
+
|32||5031||Jump backward if not
|- style="background-color: #ccccdd;"
 
|1022||005007||CLR PC                  ||Start loaded bootstrap with jump to 0
 
 
|}
 
|}
  
Note that the INIT pulse caused by hitting the [[front panel]]'s 'Start' button will clear the Bus Adddress register, so that the loaded block will be placed at location 0; and the Disk Address register, so that sector 0 will be read. If the drive's heads are not on cylinder 0, since a seek on an RL01/02 is ''relative'', a 'Read Header' command would have to be done before a seek could be commanded (or the [[device driver]] must remember the current cylinder), and that all would require a fair amount of code. To ensure that the drive is on cylinder 0 for the bootstrap, the drive should be power cycled before starting the bootstrap. -->
+
Start at 21; the loaded [[operating system]] will overlay the bootstrap.
 +
<!-- Note that the INIT pulse caused by hitting the [[front panel]]'s 'Start' button will clear the Bus Adddress register, so that the loaded block will be placed at location 0; and the Disk Address register, so that sector 0 will be read. If the drive's heads are not on cylinder 0, since a seek on an RL01/02 is ''relative'', a 'Read Header' command would have to be done before a seek could be commanded (or the [[device driver]] must remember the current cylinder), and that all would require a fair amount of code. To ensure that the drive is on cylinder 0 for the bootstrap, the drive should be power cycled before starting the bootstrap. -->
  
 
[[Category: OMNIBUS Storage Controllers]]
 
[[Category: OMNIBUS Storage Controllers]]

Latest revision as of 21:30, 26 May 2021

The RL8-A disk controller for the OMNIBUS PDP-8s was for the RL01 and RL02 disk drives. It could be set under program control to either 8-bit or 12-bit mode; in the latter, a sector contained 170 words, with 8 bits left unused. (These drives protect the data, and sector headers, with separate CRCs.)

The RL8-A was a hex board, the M8433. It had a 40-pin Berg connector which receives a special inter-drive cable (round in cross-section, with special locking connectors). The cable runs to the first drive; up to 4 drives can be connected to a single controller, using a bus running from one drive to the next, with a terminator in the last drive of the string.

It can be configured as device 60/61 (first controller) or 62/63 (second controller); its normal data break priority is 0, but it can be jumpered to use 1 instead.

Controller capabilities

The controller and drive combination can execute 8 different commands:

  • Maintenance
  • Reset
  • Get Status
  • Seek
  • Read Header
  • Write Data
  • Read Data
  • Read Data Without Header Check

Device instructions

The RL8-A is controlled with 14 instructions:

Code Mnemonic Function
6600 RLDC Clear controller, all register
6601 RLSD Skip on function done, clear if set
6602 RLMA Load memory address register
6603 RLCA Load command register A
6604 RLCB Load command register B
6605 RLSA Load sector address register
6607 RLWC Load word count register
6610 RRER Read error register
6611 RRWC Read word count register
6612 RRCA Read command register A
6613 RRCB Read command register B
6614 RRSA Read sector address register
6615 RRSI Read silo word
6617 RLSE Skip on composite error, clear if set

Device registers

The RL8-A controller includes 7 internal registers:

Register Abbreviation
Command Register A CA
Command Register B CB
Memory Address Register MA
Sector Address Register SA
Word Count Register WC
Error Register ER
Silo Buffer Register SI

Command Register A

During a seek:

DIR HS Unused CYL DIFF
11 10 09 08 07 06 05 04 03 02 01 00
DIR - Direction
HS - Head Select
CYL DIFF - Cylinder Difference (distance to move)

During a data read/write:

Unused HS Unused CYL
11 10 09 08 07 06 05 04 03 02 01 00
HS - Head Select
CYL - Cylinder

Command Register B

Unused MAIN MODE IE DRVSEL EMA FUNC
11 10 09 08 07 06 05 04 03 02 01 00
MAIN - Maintenance
MODE - 12- OR 8-bit mode
IE - Interrupt Enable
DRVSEL - Drive Select
EMA - Extended Memory Address
Function Code Function
0 Maintenance
1 Reset
2 Get Status
3 Seek
4 Read Header
5 Write Data
6 Read Data
7 Read Data, No Header Check

Error Register

DCRC/HCRC OPI DLT/HNF Unused DE DRDY
11 10 09 08 07 06 05 04 03 02 01 00
DCRC/HCRC - Data CRC/Header CRC
OPI - Operation Incomplete
DLT/HNF - Data Late / Header Not Found
DE - Drive Error ('Get Status' will provide details)
DRDY - Drive  Ready

Silo Buffer Register

During a 'Read Header' command - word 0:

Unused CA0 HS SECTOR
11 10 09 08 07 06 05 04 03 02 01 00

During a 'Read Header' command - word 1:

Unused CYLINDER CA8-CA1
11 10 09 08 07 06 05 04 03 02 01 00

During a 'Get Status' command - word 0:

Unused DT HS CO HO BH STATE
11 10 09 08 07 06 05 04 03 02 01 00
DT - Drive Type
HS - Head Select
CO - Cover Open
HO - Heads Out
BH - Brush Home
State Code State
0 Load Cartridge
1 Spin Up
2 Brush Cycle
3 Load Heads
4 Seek
5 Lock On
6 Unload Heads
7 Spin Down

During a 'Get Status' command - word 1:

Unused WDE CHE WL STO SPE WGE VC DSE
11 10 09 08 07 06 05 04 03 02 01 00
WDE - Write Data Error 
CHE - Current Head Error
WL - Write Lock
STO - Seek Time Out Error
SPE - Spin Error
WGE - Write Gate Error
VC - Volume Check
DSE - Drive Select Error

Bootstraps

Address Data Comments
21 7600 Clear accumulator
22 6600 Clear controller
23 7332 Generate constant
24 6605 Load SA with 20
25 1021 Load constant into accumulator
26 6607 Load WC
27 2327 Generate constant
30 6604 Load CMD B
31 6601 Skip on done
32 5031 Jump backward if not

Start at 21; the loaded operating system will overlay the bootstrap.