How to add GRiD Compass platform?

[JDat]

How to add another platform?
I want to try port ELKS on GRiD Compass 1101, 1129, 1131.

I have some hardware information regarding GRiD Compass.
There is d8254 PIC but on different I/O ports (0x00 and 0x02). IRQs by default are mapped in INT20h - INT27h. I can edit ports.h to fix it.

Instead of PIT Compass have "screen line IRQ" (16 kHz). This looks like some editing in arch and software logic.

Need to write bubble memory and GPiB FDD/HDD drivers, but have general idea how it all works on hardware level/protocol. Serial port and modem is also just another driver writing. Got an idea how to write these.

Local console (screen and keyboard)? Also have some information how it works. This can be done via CCPROM (BIOS for Compass) API or directly by accessing hardware.

So far I can not understand how was added 801xx and PC-98.
How to add another platform correctly? Looks like there is lot of editing, including config/make files...

[ghaerr]

Hello @JDat,

Thanks for your interesting ELKS. There should be a straightforward path to getting ELKS running on GRiD.

I don't suggest worrying yet about exactly how to create a new "platform" in ELKS, but first get the various devices working an a basic ELKS porting running, then the platform can be arranged.

You can start in elks/arch/i86/kernel, where the IRQ, and TIMER devices are coded. These have names like irq-8018x.c and timer-8018x.c. You'll want to create new versions, perhaps irq-grid.c, etc. You can define a new "architecture" like CONFIG_ARCH_GRID in .config, which will then allow you to change elks/arch/i86/kernel/Makefile to include your devices rather than 8018X, etc.

You may want to add a new section for CONFIG_ARCH_GRID in include/linuxmt/config.h.

The console code is in elks/arch/i86/drivers/char, and bubble memory block device driver would go in ../block.

Take a look at these and we can continue discussing the port. You'll want to understand how ELKS operates using the target-specific code mentioned above, and what problems there might be. There will also likely be special consideration about boot, but I don't know enough about GRiD to get into discussion that yet.

Looks like there is lot of editing, including config/make files...

Yes, there might be, but I suggest getting something running before doing all that.

Thank you!

[JDat]

Wow! That was really fast replay! Thank you very much!

I am just a beginner in C and Linux/ELKS kernel stuff. That mean I am making lot of mess in C code. Never compiled Linux kernet. Only using Linux as desktop OS.

I have following idea: I will experiment with kernel and do hardcore patching in 8018x or PC-98 without git pull. Maybe I'll simply fork ELKS and do experiments. When I'll get something working, we can discuss how to integrate my patches into production ELKS.

I'll start with sector read from bubble/FDD, because not yet understand all details. So far I can execute only 2 Kbytes of my own ASM code.

Than I'll try to customize kernel according to memory layout for GRiD and load it into RAM. I am not planning to use CCPROM API. I'll disable original timer interrupt. Maybe I'll use CCPROM API for showing text on screen. This is really slow and long process because I also need to continue hardware research for GRiD. Including PAL IC reversing, schematics, disassembling CCPROM code, Keyboard controller code , external FDD controller code.

I hope, that on one day I can get ELKS on GRiD.

Some information about GRiD hardware. Just for fun and curiosity. Not published before outside GRiD community:

GRiD have 8086 CPU and 8087 FPU @ 5 MHz.
Programmed Array Logic (PAL) based Video subsystem. Each pixel on screen can be individually addressed. So we have graphical only display.

GRiD also have following peripheral devices:
Keyboard controller. Also used as watchdog for pseudoDMA timeout to prevent stall.
8274 UART controller with RS232/RS422 and HDCL support. For GRiD network, Serial printers, Mouse...
Intel 7220 bubble memory storage 384 kBytes
Ti TMS9914A GPiB controller for peripiheral devices like external Floppy and Disks. Also for GPiB Printers.
Racal-Vadic Modem 300/1200 baud. Probably not compatible with Bell 2002 standard.
On Modem board there is also 8 Bit DAC connected to Internal Speaker. Can be used as COVOX thing.
RTC clock.
Hardware devices are mapped into memory. We can access them by reading writing in D000:offset.

There is no timer 8253/8254, but IRQ happens regularly from video hadware after every line is drawn on screen. This happen with ~16.4 kHz.

CCPROM - It is like BIOS for IBM XT, but... Don't call it BIOS for GRiD Compass, because BIOS is for IBM PC! GRiD Inc. called it CP or CCPROM.

CCPROM is 16 kBytes.
It have initialization code for all peripherals.
It have Font 5x8 pixels per character.
There are routines for printing char or line with CF/LF and BS handling (myve even more). Automatic screen scrolling, cursor stuff, etc.
More interesting thing inside CCPROM is Multitasking. There are routines for memory allocation, IPC message exchange, task creation and switxhing between tasks, including task sleeping, etc.
Drivers for Bubble memory and GPiB interface.

Boot process happens in following:
CCPROM set stack to 3000:000 and then read 1st sector and check for string "System Disk!" If present, then read 4 more sectors (2 kByte boot loader) code and put this code into 2000:0000, verify checksum and ,if everything is OK, jump to 2000:0006.

There are available lot of API calls. It is organizes as jump table. You can so call far FFFE:xxxx to access API.
There are API for keyboard programming. Install your own IRQs, enaable/disable IRQs. Memory, message/signal and task management API. API for reading 256 byte sectors from bubble memory. API for reading GPiB FDD/HDD 512 byte sectors with LBA addressing. Write text to screen (char or line). Etc.

Memory layout:
0x00000 - 0x003FF - Interrupt table
0x00400 - 0x0297F - Screen buffer. Pixel addressable. 320 x 240 pixels (more for 113x series because 512 x 256 pixels)
0x02980 - 0x0697F - CCPROM data area. Pointers for soft font, Pointers to GPiB and Bubble drivers, multitasking, memory management variables.
0x06980 - 0x3FFFF - Available RAM 256 kBytes ( up to 0x7FFFF for 512kByte models)
0x80000 - 0x9FFFF - EPROM for user programs (not researched yet). Can boot from here or store read only files.
0xC0000 - 0xCFFFF - Factory diagnostic ROM. No info how to connect.
0xD0000 - 0xDFFFF - Memory mapped I/O Devices: Bubble, GPiB, Keyboard, RTC, Modem, Serial
0xE0000 - 0xEFFFF - PseudoDMA using 8086 rep stosw code. Only one address used. Not fully researched yet
0xF0000 - 0xFFFFF - CCPROM - bootstrap code, init code, multitasking, memory managements, bubble & GPiB drivers, Keyboard and screen routines, Build in Font, entry points to API calls.

I/O address space:
0x0 - 0xF - 8259 Interrupt controller (actually only 2 addresses used).
IRQs are mapped as 0x20 - 0x27 in Interrupt table.

int8087 EQU 0
intGpib EQU 1
intKeyboard EQU 2 ; (Never used on CCOS, used only in CCPROM)
intSysTick EQU 3 ; (intHorisontalSync on compass) ~16.4 kHz
intModem EQU 4
intBubble EQU 5 ; (Never used on CCOS, used only in CCPROM)
intSerial EQU 6
intGlitch EQU 7