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G.I. CTS256A-AL2 reimplementation on Z-80

Version 0.2.0-alpha

History

v0.3.0-alpha

  • reworked the YLDCTS yield routine and the idle loops in the CTS256 module, to fix issues in the handling of separators;
  • added an "Oddities" section in the README.md document;
  • reworked the rules encoding macros.

v0.2.0-alpha

  • convert text to uppercase to circumvent parsing errors in lower case text by the CTS256 module;
  • add rules debugging mode |r1.

v0.1.0-alpha

  • converted code-to-speech rules to text using macros to encode them;
  • splitted the source code into separate parts.

Files

Overview

This project aims at reimplementing the code contained in the Text-To-Speech processor CTS256A-AL2 from G.I. (General Instruments) to target the Z-80 processor. The CTS256A-AL2 is a companion chip for the SP0256A-AL2 "Narrator(tm)" voice synthesizer from the same company. Its role is to convert ASCII English text to Allophone codes for the SP0256A-AL2.

Some time ago, I disassembled and commented the original code of the CTS256A-AL2, to understand how it works. I also wrote a small C program to extract the conversion rules encoded in the chip. See CTS256A-AL2.

Later I wrote a pair of programs in C++, one to emulate the SP0256A-AL2 and produce audio from a stream of allophone codes, the other to emulate the TMS-7000 CPU (or G.I.'s PIC7041 in this case) on which the CTS256A-AL2 processor is based. See SP0256_CTS256A-AL2.

In this project, I first wrote a small C++ program to convert the disassembled TMS-7000 source code of the CTS256A-AL2 into Z-80 code.

Then I integrated the generated source code into an executable application that can be run on a TRS-80 Model 4 either on CP/M or LS-DOS 6.3, and into a resident driver and a filter for LS-DOS 6.3.

To use those programs, it is just needed to connect the SP0256A-AL2 in parallel mode to the printer port. For the LS-DOS driver or filter, 128K or more RAM memory are required, because the resident code is loaded in banked memory. Sufficient memory must also be available in the low driver area (below $1300). Note that the filter module can also be attached to any device other than the printer *PR.

The CP/M version should also run on other Z-80-based platforms. The output is sent to the standard BDOS LIST device.

How to use it

CP/M

There is currently no resident CTS256 driver for CP/M. It is only possible to run the executable to say a string or to read aloud a text file.

Executable mode

CTS256 string to say

or

CTS256 filespec

The string or the text file just contain some English ASCII text. Some escape codes are recognized:

  • |d1 to enable debug output of allophone mnemonics to the screen;
  • |d0 to disable it;
  • |e1 to echo the ASCII text sent to the CTS256 module;
  • |e0 to disable it;
  • |r1 to enable the rules debugging mode - try CTS256 |e1 |r1 This is a test.;
  • |r0 to disable it.

Allophone mnemonics can also be directly converted to codes and sent to the SP0256 device if they are enclosed inside brackets. Refer to the SP0256A-AL2 data sheet for more info about the allophone mnemonics.

Example (the mnemonics can be spaced):

  • CTS256 I'm a [KK3AAMMPA3PPYY1UW1PA3TT2ER1]

The SP0256 allophones stream is sent to the LIST device. Use the CP/M CONFIG tool to re-assign the LIST device if needed (for example, a serial port).

LS-DOS 6.3

Executable mode

CTS256 string to say

or

CTS256 filespec

The usage is identical to the CP/M executable version previously discussed.

The output is sent to the *PR device. It can be routed to another device or a file using the LS-DOS ROUTE command.

Driver mode

SET *CT [to] CTS256/DVR

The driver is assigned to a device name, eg: *CT. Any text sent to that device is converted to allophones and sent to the *PR printer device. The *PR device can be routed to any other output device (eg: serial port) or a file. Refer to the LS-DOS manual.

Example on how to use it:

COPY FALKEN/TXT *CT

In BASIC:

10 ON ERROR GOTO 10000
20 OPEN "O",1,"*CT" 'the device name given at the SET command
30 ON ERROR GOTO 0
40 PRINT #1, "|e1 This is a test."
50 CLOSE
60 END
10000 'Error handler
10010 PRINT "Can't open driver. Error code:";ERR
10020 RESUME 60

Filter mode

SET *CT [to] CTS256/FLT
FILTER *PR [using] *CT

The filter is assigned to a device name, eg: *CT. Then it is attached to the printer device *PR using the FILTER command. Any text sent to that device is converted to allophones and sent to the filtered device. It should also be possible to attach the filter to the Comms Link device *CL (I didn't try...).

Note that it is not possible to use the CTS256/EXE program if the filter is attached to the *PR device!

Example on how to use it:

LIST FALKEN/TXT (P)

In BASIC:

10 LPRINT "|e1 This is a test."

How to assemble it

I selected the assembler ZMAC from Georges Phillips to build the binaries under Windows.

The same source is used to assemble the different versions. The parameter -P0=v, which defines the corresponding system variable @@0 to the same value v, selects which parts of the code will be selected using conditional assembly:

  • -P0=2 for the CP/M executable CTS256.COM;
  • -P0=3 for the LS-DOS 6.3 executable CTS256/CMD;
  • -P0=4 for the LS-DOS 6.3 driver CTS256.DVR;
  • -P0=5 for the LS-DOS 6.3 filter CTS256.FLT.

CP/M

There is currently no resident CTS256 driver for CP/M.

Executable mode

ZMAC --zmac CTS256.ASM -P0=2 --od . --oo CIM,LST,BDS
move /Y CTS256.CIM CTS256.COM

Then copy CTS256.COM to a CP/M disk.

LS-DOS 6.3

Executable mode

ZMAC --zmac CTS256.ASM -P0=3 --od . --oo CMD,LST,BDS

Then copy CTS256.CMD to an LS-DOS 6 disk.

Driver mode

ZMAC --zmac CTS256.ASM -P0=4 --od . --oo CMD,LST,BDS
move /Y CTS256.CMD CTS256.DVR

Then copy CTS256.DVR to an LS-DOS 6 disk.

Filter mode

ZMAC --zmac CTS256.ASM -P0=5 --od . --oo CMD,LST,BDS
move /Y CTS256.CMD CTS256.FLT

Then copy CTS256.FLT to an LS-DOS 6 disk.

How it works

The original CTS256A-AL2 disassembled source code has been converted to Z-80 instructions using the conversion program MCS7000_to_Z80.cpp. Some fixes have been applied to fix some issues as JR value errors and the unsupported MPY instructions. Fortunately the MPY instructions were easy to fix with ADD instructions (the multiplicators were 2 and 3). A call to YLDCTS (yield) is also inserted in the idle loops of the CTS256A, to allow some kind of cooperative multitasking between the application and the CTS256 re-implementation. The converted code is named the "CTS256 module" in this discussion.

The CTS256A-AL2 memory space is handled as:

Registers R0-255, with the stack and the "internal" device buffers [0000-00FF]:

  • The registers are mapped to a region of 256 bytes in the Z-80 RAM space, and the first 128 registers can be accessed via the Z-80 register IX. Because the endianness of the TMS-7000 CPU is reversed wrt. the Z-80, the order of the registers is reversed. This is needed so the MOVD and DECD instructions using register pairs can work correctly. So, if IX is initialized to point to R0, the register R1 is accessed via (IX-1), R2 via (IX-2) and so on. The registers A and B which are mapped to R0 and R1 in the real TMS-7000, are not mapped in the Z-80 re-implementation. Instead, they simply use the corresponding Z-80 registers A and B (the Z-80 register A is saved to C when needed).
  • The TMS-7000 stack space is remapped to a "local" stack space of 64 bytes at CTSSTK. The Z-80 stack pointer is switched between the user stack and the local CTS256 module's stack, when the context is switched between the "user" mode and the "CTS256 module" mode. The Z-80 registers are also saved/restored upon context switching.
  • The "internal" device buffers are not used. The CTS256 module is configured to use an external RAM space of 4kB (1000H).

I/O Ports P0-P255 [0100-01FF]:

  • The ports are mapped to a region of 256 bytes in the Z-80 RAM space, and the first 128 ports can be accessed via the Z-80 register IY. Here the order of the ports is not reversed, as there is no need for that. Some ports are used to write/read the busy status of the CTS256 module, to enable/disable interrupts and to trigger them.

Parallel input from host computer [0200-0FFF]:

  • The ASCII text bytes from the host are read at the address 0200H. In the re-implementation, this address is mapped to PARLINP. When the host sends a byte to the CTS256 module, it writes the byte at that address, then triggers the INT3 interrupt if enabled.

SP0256 address space [2000-2FFF]:

  • The CTS256A-AL2 device writes the SP0256 allophone codes on the address bus in the space [2000-2FFF]. If an allophone is ready to be sent to the SP0256, it enables the INT1 interrupt. When the SP0256 is ready to receive a byte, it triggers INT1 and the interrupt handler sends the byte via the TMS-7000 address bus to the SP0256. In the re-implementation, when a byte is ready to be sent, the INT1 bit is set and the CTS256 module "yields" to the user application. The module wrapper then triggers INT1. The module's INT1 handler sends the byte to the device's address space in a 256-byte dummy buffer at SP0256 and the LSB of the address is written to R27. Then the wrapper reads the LSB of the address in R27 and sends it to the output device.

ROM code space [F000-FFFF]:

  • The original TMS-7000 code has been converted to Z-80 using the conversion tool written in C++. This code space also contains the packed text-to-speech conversion rules, unmodified.

Operation

  • After the CTS256 module is loaded into memory, it is first configured and prepared to be booted. The configuration initializes the I/O ports to:
    • use the parallel input mode (vs. serial) from the app (APORT=xxxxx000),
    • use the external memory space for the input and output buffers (APORT=xxx1xxxx),
    • any delimiter to trigger the conversion (APORT=1xxxxxxx).
  • Afterwards, the CTS256 module is "booted". The user stack is saved, the local stack pointer is initialized and the initialization code of the module is executed. At the end of the initialization code, the string O-K. is converted and ready to send to the device output.
  • It then enters an idle loop, and in the re-implementation a call to a yield routine YLDCTS is made, giving the control back to the application code. The YLDCTS routine first checks if INT1 is enabled, and if so, calls the INT1 handler to let the module send the next allophone; reads the allophone code and send it to the host device; and repeats until there are no more allophones to send (INT1 disabled). Then the YLDCTS routine saves the context (Z-80 registers) and the local stack pointer, switches SP to the application stack, restores the application registers and returns to the application.
  • When the application needs to send a character to the CTS256 module:
    • it stores the character into PARLIMP;
    • switches the context back to the CTS256 module;
    • triggers INT3 to let the module read and process the incoming character;
    • returns to the idle loop from where YLDCTS was called;
    • executes the module code to do the text-to-speech conversion, until YLDCTS is again invoked in the idle loop.

Oddities

While studying the CTS256A-AL2 module I found a number of oddities:

  • The module doesn't handle the lower case letters properly. For example, "rider." in lower case generates {[R]=[RR1]} {[I]=[IH]} {[D]=[PA2 DD2]} {[ER]=[ER1]} {[.]=[PA5 PA5]} whereas "RIDER." in upper case generates {[R]=[RR1]} {[I]^%=[AY]} {[D]=[PA2 DD2]} {[ER]=[ER1]} {[.]=[PA5 PA5]}. I found that the FETCH routine in the ROM does not perform the conversion to upper case. The conversion is done in GNEXT, which calls FETCH. But in the pattern check routines, FETCH is directly called, so the lower case chars are not converted. To fix that I had to add instructions to convert the characters to upper case.
  • When I converted the rules to plain text, I found a pattern symbol '$1F' (symbolized as '$') that is not recognized by the encoding routine in the ROM. I suspect that the rule [I]$% = [AY] is wrongly encoded, and should be in fact [I]D% = [AY], if I refer to the original document from the Naval Research Laboratory: 
     [IZ]%=/AY Z/
 [IS]%=/AY Z/
 [I]D%=/AY/
 +^[I]^+=/IH/
 [I]T%=/AY/
 #^:[I]^+=/IH/
    And the corresponding rules extracted from the CTS256A-AL2 ROM: 
     [IZ]% = [AY ZZ]
 [IS]% = [AY ZZ]
 [I]$% = [AY]		; and not [I]D% = [AY]
 +^[I]^+ = [IH]
 [I]T% = [AY]
 #*[I]^+ = [IH]

Program structure

The code is divided into the following blocks:

Driver/Filter Loader

This optional block is assembled only for the LS-DOS 6.3 versions of the Driver CTS256/DRV and the Filter CTS256/FLT. It checks the environment to ensure that:

  • the loader is invoked by the DOS command SET *xx CTS256/ext;
  • there is enough memory space in low driver memory to load the Jumper between $LOW and $1300;
  • there is at least one bank of 32K extended memory available.

Then:

  • it reserves one bank of 32K extended memory;
  • it initializes the Jumper module to fix some absolute addresses for its relocation to low driver memory;
  • it moves the Jumper to low memory;
  • it moves the Driver, the link module, the wrapper and the CTS256 module to the extended memory bank;
  • it initializes the Driver.

Jumper module

This optional block is assembled only for the LS-DOS 6.3 versions of the Driver CTS256/DRV and the Filter CTS256/FLT.

This module is called by LS-DOS when an I/O operation has to be done with the driver/filter. Its role is to activate the extended memory bank containing the main part of the code, to call the code in banked memory and to restore the normal memory banking before returning control to LS-DOS. A small stack in low memory is also used during the activation of the memory bank. The fact that the banked memory must be mapped to high memory space (8000-FFFF) explains why the Jumper memory must be loaded in the low driver memory space (between $LOW and $1300).

Driver module

This optional block is assembled only for the LS-DOS 6.3 versions of the Driver CTS256/DRV and the Filter CTS256/FLT.

This module handles the @PUT and the filter's @CTL requests from the DOS.

The @PUT handler:

  • handles the parameter sequences |pn;
  • handles the square brackets to enable/disable the allophone mnemonics parser;
  • else sends the character to the CTS256 module or the allophone mnemonics parser.

The @CTL handler sends the SP0256 codes produced by the CTS256 module to the output device (*PR or other).

Exec module

This optional block is assembled only for the LS-DOS 6.3 and CP/M versions of the executable application.

This module checks if the command line argument is the name of an existing (text) file.

  • If yes, the input for the processing is taken from the file.
  • If not, the input is taken from the command line.

The processing done by this module is essentially the same as in the Driver module.

Link module

This module contains:

  • a protected version of the LS-DOS $SVC service caller, where the stack is temporarily switched back to low memory, and the interrupts are disabled before restoring the stack pointer;
  • LS-DOS and CP/M versions of the @DSP, @PRT;
  • the incoming character handler, sending the character either to the CTS256 module or to the allophone mnemonics parser;
  • the "echo" |e1 and "debug" |d1 handlers;
  • the intro text.

SP0256 helper module

This module contains:

  • the allophone mnemonics parser;
  • the allophone code to mnemonic converter;
  • the allophone mnemonics table.

CTS256 Wrapper module

This module contains:

  • the BOOTCTS code to initialize and boot the CTS256 module;
  • the YLDCTS yield routine called by the CTS256 module's idle loop (with context switching);
  • the SENDCTS resume routine to resume the CTS256 module execution (with context switching).

CTS256 module

This module contains essentially the code generated by the TMS-7000 to Z-80 source code converter, with some fixes and adaptations.

The C++ conversion program MCS7000_to_Z80

This small program had been written in order to convert the original CTS256A-AL2 disassembled source code into Z-80 instructions. This was developed ad-hoc to convert only the TMS-7000 instructions that were used by the CTS256A-AL2 device. So in its current state it could not be used for other applications.

This utility is built on Windows using this Visual Studio C++ compiler command:

cl /EHsc MCS7000_to_Z80.cpp

Then the generated executable can be used to convert the source code:

MCS7000_to_Z80 <CTS256A.ASM >CTS256A_Z80.ASM

where CTS256A.ASM is the original CTS256A-AL2 disassembled source code and CTS256A_Z80.ASM is the converted Z-80 code.

To do next

  • Reduce the code size, by removing unneeded generated instructions (LD C,A and LD A,C).
  • Support for exception words EPROM images (as long as they don't contain executable code); see if possible.
  • A special flag to enable the output of the matching conversion rules found during the processing.
  • A driver mode for CP/M (this can be quite challenging!).
  • A Model I/III LDOS version (executable mode only).

Copyright notice

Microchip, Inc. holds the copyrights to the SP0256-AL2 design and ROM Image, and to the CTS256A-AL2 ROM Image. Microchip retains the intellectual property rights to the algorithms and data the emulated device CTS256A-AL2 contains.

GPLv3 License

Created by Michel Bernard (michel_bernard@hotmail.com) - http://www.github.com/GmEsoft/TRS80_CTS256A-AL2

Copyright (c) 2024 Michel Bernard. All rights reserved.

This file is part of TRS80_CTS256-AL2.

TRS80_CTS256-AL2 is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

TRS80_CTS256-AL2 is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with TRS80_CTS256-AL2. If not, see https://www.gnu.org/licenses/.