Is there any point nannying an older MPU using an MCU? - Page 1
Forum section: electronics / general

author: technix
author_rank: Super Contributor
timestamp: March 19, 2017, 02:06:46 pm
content: This is about the 80C88 and AT91SAM9260 I bought. I had the idea of nannying it with a modern MCU that offers it a reference clock, a POR, power rail timing and USB to Serial link. Is this appropriate?For the 80C88, the nanny MCU would be PIC16F1455, providing a 4MHz reference clock, a serial connection and POR sequence.For the AT91SAM9260, the nanny MCU would be STM32F103CB, a serial connection over USB, POR and power sequence, and maybe a JTAG.

author: Ian.M
author_rank: Super Contributor
timestamp: March 19, 2017, 02:21:11 pm
content: Its not whether you 'nanny' it with another MCU or a SBC, its where you want to be on the spectrum of choices between the complete purist route, including a reconditioned VT100 terminal and a date code cutoff for all chips used, and the other end - hardware emulation as a soft-core in a current FPGA, with a high speed modern interface to a host system. If your interest is retro hardware interfacing, then using a period equivalent CPU or its direct descendent, but giving a modern MCU full bus access is likely to make the system a lot easier to bring up as all sorts of stuff can be emulated with the MCU until you have built it for real. If its the software side of things - well that's what software emulation is for.

author: westfw
author_rank: Super Contributor
timestamp: March 20, 2017, 01:49:54 am
content: Well, I built several "z80 nannied by an ATmega32" boards recently. They're sort-of neat, but I'm not really sure if there is that much of a "point" to it. One thing that is moderately interesting is justhow differenta RAM-rich environment can be. The ATmega32 has 32k of flash, and the Z80 has 64k of RAM, so those are "pretty close", right? Not really; for some things, the relevant comparison is 2k ofRAMin the m32, vs 64k in the Z80...OTOH, I have some ARM7TDMI chips that I'm think I should just throw away; obsoleted by the Cortex chips, these are neither historically not technically interesting. I think. (Ditto my early Luminary CM3 chips? Or do those qualify as "collectibles"?)

author: technix
author_rank: Super Contributor
timestamp: March 20, 2017, 10:28:15 am
content: Quote from: westfw on March 20, 2017, 01:49:54 amI don't think the nanny chip should sit in the front side bus, so the memory discrepancies are not felt. Although for the AT91SAM9260 board the nanny can access the main processor's 64MB RAM, through DMA requests over SPI bus. 12MHz SPI are fast.I have some ARM7TDMI chips too, LPC2103, and I am keeping them for the sake of having some ARM7 chips to play with.I am even buying older chips that can run Linux, playing with the idea of creating an DIY SBC with modern-ish features. I have acquired AT91SAM9260 and its accompanying memory (64MiB SDR SDRAM from Micron and 512MiB SLC NAND from Samsung) for the project.

author: obiwanjacobi
author_rank: Super Contributor
timestamp: March 20, 2017, 11:51:44 am
content: I have a Z80 nannied by a PSoC5 (see signature).This System Controller provides DMA, implements IO including a virtual channel over USB to the PC where the keyboard strokes are intercepted and sent to the Z80 system. It provides a separate debug UART channel for debugging/tracing etc.I think its fun!

author: westfw
author_rank: Super Contributor
timestamp: March 20, 2017, 09:53:05 pm
content: QuoteI'm not sure what you mean; but *I* meant that programming any system with essentially ALL RAM seems fundamentally different than programming any chip with mostly flash and just a bit of RAM, entirely separately from whether you are using a "nanny" chip..

author: technix
author_rank: Super Contributor
timestamp: March 21, 2017, 09:36:40 am
content: XIP vs load and run.

author: james_s
author_rank: Super Contributor
timestamp: March 22, 2017, 06:27:25 pm
content: I never liked this approach myself. Always seemed a bit "wrong" to have a microcontroller more powerful than the primary CPU.

author: technix
author_rank: Super Contributor
timestamp: March 23, 2017, 12:24:43 am
content: Quote from: james_s on March 22, 2017, 06:27:25 pmHow powerful is PIC16F @48MHz and Cortex-M3 @72MHz anyway?

author: james_s
author_rank: Super Contributor
timestamp: March 23, 2017, 12:53:39 am
content: Quote from: technix on March 23, 2017, 12:24:43 amThat's not a trivial question to answer, but it's safe to assume that it's quite a lot more powerful than a 4.77MHz 8088.

author: technix
author_rank: Super Contributor
timestamp: March 23, 2017, 02:51:34 am
content: PIC16F @48MHz vs 80C88 @8MHz?Cortex-M3 @72MHz vs ARM926EJ-S @180MHz vs Cortex-A7 MP1 @1.2GHz?

author: brucehoult
author_rank: Super Contributor
timestamp: March 23, 2017, 07:09:50 am
content: Quote from: westfw on March 20, 2017, 01:49:54 amGosh. The ARM7TDMI is *the* chip that made ARM what it is today, taking them from obscurity in a few Newtons and Psions to the first billion feature phones!

author: grumpydoc
author_rank: Super Contributor
timestamp: March 23, 2017, 09:54:26 am
content: Quote from: technix on March 23, 2017, 02:51:34 amWell the 48MHz PIC16F's have 14K of ROM and 1K of RAM, plus are only 14 or 20 pin packages so if what you want to do fits in that envelope the higher clock speed might give you better performance unless you need to do a lot of 16 bit maths.The most memory that the PIC16's have is 56k ROM and 4k RAM (but at 32MHz max clock).The 80C88 will address a meg of memory and I guess would perform about the same on general purpose computing. Probably better despite the slower clock if you need anything more than 8 bit maths.QuoteFirst two, no idea. Latter way faster surely?

author: spudboy488
author_rank: Regular Contributor
timestamp: March 23, 2017, 11:46:39 am
content: As said, it depends on what you want to get out of it. I have a ROM-less Z80 board and I use a PIC to load the program into the 64K RAM. I did it that way because I was more interested in the nostalgia code development. Also, I didn't have a way to program (E)PROMS so all I do is dump the hex file onto a VB.net file and it transfers it to RAM. Do what makes sense to you.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: March 23, 2017, 06:13:44 pm
content: Quote from: westfw on March 20, 2017, 01:49:54 amThe Cortex-M architecture is so much better than ARM7TDMI that it's not even funny. Toss 'em! Do keep the Luminary chips, though.

author: james_s
author_rank: Super Contributor
timestamp: March 23, 2017, 06:45:08 pm
content: Or maybe throw them on ebay for a few bucks for the lot, someone might have a use for them.

author: technix
author_rank: Super Contributor
timestamp: March 24, 2017, 01:09:14 am
content: Quote from: Sal Ammoniac on March 23, 2017, 06:13:44 pmI'd like to know what exact parts do you have sporting the ARM7TDMI. Maybe it can run some flavor of Linux.

author: westfw
author_rank: Super Contributor
timestamp: March 24, 2017, 05:19:28 am
content: QuoteI'm specifically talking about the ARM7TDMI chips sold as "microcontrollers" (mostly by NXP, I think.) LPC2103, LPC2138, and similar. No MMU, No external RAM controller, just semi-reasonable attempts to bend the architecture to something it wasn't really meant to be.I don't have any complaints about the more full-featured microprocessor-style chips capable of running linux or other "real OS" (though I haven't really looked at them carefully enough to have an opinion; not my cup of tea, so to speak.) I have several pre-Cortex "embedded ARM unix" boxes (Like some Mattel Juiceboxes with Samsung S3C44B0) that I meant to do things with, and are probably obsoleted by things like Raspberry Pi (and likewise should be thrown out. But they were cheap, and don't require the same level of effort as a bare chip.)