Re: Micro IMSAI

[TheHighNibble]

Mikol,

the current firmware won't run headless. Its looking for at least the Power switch to know that you have finished building the kit.

Even with the Power switch in place, the only way you can currently set the NVRAM configuration is through the front panel switches.

That's not to say this would always have to be the way :-)

I have thought about a micro version myself, how else would I remain sane on the 14 hour flight from Australia to the US. But my last trip was cancelled by COVID-19.

On Saturday, 30 May 2020 23:37:22 UTC+10, Mikol Ryon wrote:

So I got my kit all assembled and working and I love it.

I like to be able to reproduce things so I bought a spare esp32-pico, flashed it, dropped it and Bob's yer uncle, it works.

Here's where perhaps, I get a little silly...

Now I've got a spare esp32. Hmm...could I wire up the PSRAM and SD card socket and have another one that I can use exclusively via the web interface?

Or, what if I did a super tiny 1/4 or 1/8 scale version of the whole thing? Maybe a bank of dip switches or even jumpers for the switches?

Sure, it wouldn't look accurate but I'd love a micro version. I could probably just about wire up the ram and sd card but designing a little PCB for the LEDs and switches would be beyond me.

If someone cleverer than I could do that they'd be my hero.

[TheHighNibble]

P.S. I think all the ICs would have to be SMD to make it adequately "micro".

[Udo Munk]

Small headless systems already were done plenty, for example:

https://smallcomputercentral.wordpress.com/2020/02/26/pocket-romwbw-system/

[Ted Agar]

Several months ago I started a little project intended to help me become more familiar with the ESP32 family. I purchased a ESP32 variant that had PSRAM and a microSD socket already onboard. Flashed Dave's code and fired it up to see what might happen. Came up, to a point, but I quickly became aware that I needed the front panel power switch to get very far, and that I also I would need the front panel to set the configuration. My ESP32 board had a different footprint than the PICO so I jumpered the minimal required number of pins (<10 pins as I recall) so that I could use the imsai8080esp panel to get past that point. I kept expanding on the project until I ended up with something that could potentially run the whole ball of wax. The result mostly works but has a handful of problems. Issues may be because I failed to faithfully reverse engineer the panel, or maybe problems with my retro and noisy wiring methods. Some questions came up while interpreting the design that I have yet to find answers for...

At any rate I got bored with it and set it aside.

[wb4...@gmail.com]

Hey Ted,

Once the NVRAM is properly programmed in, could all the LEDs and switches (except power) be removed?  I’m wondering about a mother/duaghter board pair, where the “necessary” parts are always with the esp32, and the LEDs, switches, etc.. are on a larger motherboard that is only plugged into when needed.

 

Also, which esp32 board did you find for this that includes the small RAM and microSD?

 

I don’t want to wreck up my nice pretty IMSAIesp anymore. I also want a smaller version that I can take when I travel!

Terry

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[Ted Agar]

Terry,

This is the ESP that I used - https://www.ebay.com/itm/ESP32-WROVER-4MB-PSRAM-TF-CARD-WiFi-Module-Bluetooth-Development-Board/152942911430?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

There are many similar ones out there.

I have intermittent issues with the microSD - it mostly works but occasionally causes BDOS errors and a reboot is necessary. I had to add pullup resistors to the microSD circuit, not sure if the values are optimal. It didn't work at all until I added them.

As Dave mentioned, the power switch is required. A single TTL chip and a SPST switch could probably synthesize that part of the front panel. LEDs are definitely not required. Or, a custom version of the firmware could make the power switch not needed and provide a different way to set the configuration.

The switches are loaded in parallel into 8-bit registers that are cascaded to form a long (32-bit) shift register. They appear to then be shifted serially into a single GPIO input pin on the esp32, if I interpreted this correctly.

You could run Udo's software on a Raspberry Pi (even the zeroW) and skip the whole hardware thing, might be less fun but easier.

- ted

 

 

From: Ted Agar

Sent: Sunday, May 31, 2020 10:22 AM

To: IMSAI 8080esp

Subject: Re: Micro IMSAI

 

Several months ago I started a little project intended to help me become more familiar with the ESP32 family. I purchased a ESP32 variant that had PSRAM and a microSD socket already onboard. Flashed Dave's code and fired it up to see what might happen. Came up, to a point, but I quickly became aware that I needed the front panel power switch to get very far, and that I also I would need the front panel to set the configuration. My ESP32 board had a different footprint than the PICO so I jumpered the minimal required number of pins (<10 pins as I recall) so that I could use the imsai8080esp panel to get past that point. I kept expanding on the project until I ended up with something that could potentially run the whole ball of wax. The result mostly works but has a handful of problems. Issues may be because I failed to faithfully reverse engineer the panel, or maybe problems with my retro and noisy wiring methods. Some questions came up while interpreting the design that I have yet to find answers for...

 

At any rate I got bored with it and set it aside.

 

 

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[James Sahm]

Hello All,

I am eagerly awaiting the shipment of my IMSAI Replica kit.  In the mean time, I was wanting to experiment with this a bit. 

I understand the shift registers toggling the power switch, but more simply (or in my case more difficultly) what are the proper gpio connections for the SD card and the PSRAM.

I have the PSRAM begin to post on startup, but then unmercifully dies with:

ets Jun  8 2016 00:22:57

rst:0xc (SW_CPU_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)

configsip: 188777542, SPIWP:0xee

clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00

mode:DIO, clock div:1

load:0x3fff0018,len:4

load:0x3fff001c,len:4492

load:0x40078000,len:13324

ho 0 tail 12 room 4

load:0x40080400,len:3796

entry 0x40080624

I (353) psram: This chip is ESP32-PICO

I (354) spiram: Found 64MBit SPI RAM device

I (354) spiram: SPI RAM mode: flash 80m sram 80m

I (357) spiram: PSRAM initialized, cache is in low/high (2-core) mode.

I (364) cpu_start: Pro cpu up.

I (368) cpu_start: Application information:

I (373) cpu_start: Project name:     imsaisim_esp32

I (378) cpu_start: App version:      v1.9.1

I (383) cpu_start: Compile time:     Sep  8 2021 15:28:40

I (389) cpu_start: ELF file SHA256:  8a0e39da91675446...

I (395) cpu_start: ESP-IDF:          v4.0.2-4-g877a28e05

I (401) cpu_start: Starting app cpu, entry point is 0x40081b58

I (392) cpu_start: App cpu up.

E (898) spiram: SPI SRAM memory test fail. 130965/131072 writes failed, first @ 3F800000

 E (898) cpu_start: External RAM failed memory test!

abort() was called at PC 0x40081c33 on core 0

So it is sort of recognizing the SPRAM.  Absolutely zero luck with the SD card reader.. soldered wires directly to a mSD card adapter as the socket and no joy there at all at any point.  In theory, is should pass through... Other card slot boards I have are 6pin style:  CS, SCK, MOSI, MISO, VCC, GND.

In any case just looking to tinker around until my kit is here for the big build.  Any pointers or like minded people who'd be willing to help appreciated!

What an incredible project!!

-Jim

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[TheHighNibble]

Jim,

if you are breadboarding it, then it's highly unlikely to work.

The PSRAM interface is running at 80MHz. I had to "tune" the PCB track layout and beef-up the ground plane "shielding"  to get it to work - took a few attempts.

Also the uSD is based on an 8-wire 4-bit SD bus mode @40Mhz not the usual basic 6 wire microcontroller SPI bus mode (low speed). Again this will be susceptible to noise on a breadboard.