Picaxe18M2 as loader/xtal/EEPROM for Prop?

TonyWaite

Some thoughts are so dumb that one should hesitate before sharing them.

But what if ...

... one could configure the new Picaxe 18M2 to replace the crystal and EEPROM in a Prop circuit; the 2K memory of the 18M2 booting the Prop; the Prop then loading from SD-card.

You could do it, but I can't think of any advantage ...

T o n y

Leon

The internal oscillator on the 18M2 won't be stable enough, and the EEPROM won't be accessible to the Propeller.

legoman132

Could the Picaxe interface to an SD card? because we could have it load a start-up program into the prop, which would allow the user to choose a program file off of the SD card (.binary, .eeprom, or neither?). Then the prop would tell the Picaxe what program the user wanted, and the Picaxe would load that program into the prop. Once the user is done with that program the prop can tell the Picaxe to load the "choose file" program and repeat the cycle. Don't see why you would want to use it as an xtal though...

Mike Green

The PICAXE series doesn't have the facilities for managing the FAT file system on an SD card. It would need over 1K of RAM for sector buffers and other working space. It probably would need about twice as much program space as on the largest PICAXEs, maybe more.

You'd be better off just attaching the SD card to the Propeller and having a loader in a pre-programmed and write-protected EEPROM on the Propeller. It's been done before several different times. There was even a kiosk controller using FemtoBasic to load programs off an SD card choosing from a simple list.

tonyp12

I'm also have been thinking about using a single chip to replace
USB and eeprom.

This chip is as low end I can find that still have USB2.0
and over 32kb of flash to emulate a 32k eeprom.
and still have room for it's own software.


Freescale 8bit with 60k flash. ($3 @ 1000)
Needs crystal for USB to work, so the prop could to share it.
http://www.mouser.com/ProductDetail/Freescale-Semiconductor/MC9S08JM60CLD/?qs=y2kkmE52mdOO7K2i3bnnvw%3d%3d


Other potential chip:
TI MSP430F5503, only 32kb flash but with some code compression of the emulated 32k eepreom it's own program could fit.
http://focus.ti.com/docs/prod/folders/print/msp430f5503.html

Mike Green

@tonyp12,
Very few Propeller programs are anywhere near 32K in length. The end of the EEPROM is padded with zeroes when it's written, so the TI chip with 32K of flash will work for most cases. Remember that the Propeller doesn't need an EEPROM if it's loaded over the serial link on I/O pins 30/31.

Cluso99

RamBlade eeprom boot code uses <1.8K longs meaning <7.2KB as it's minimal boot code from an SD card.

It uses the Femto driver so the I2C could be stripped reducing the code by ~1KB and there is other code that can be removed too, for an even smaller boot. So, my guess is that a minimal boot code for the Prop to boot from SD could be done <4KB.

However, unless you can add some serious features, then any chip >$1 is not woth it as the 32KB eeprom can be obtained in qty for less than this.

Of course, USB2.0 is a candidate. The FTDI chip is just too expensive for what it does IMHO.

I have done no Prop code for 6 mths due to other pressures. ASAP I want to take a look and see what, if anything, can be done to take Brad's USB serial code (to the PC) and see if we can reduce it's resources and cogs, so we can do minimal USB to PC in the Prop itself. ??? (sorry I keep forgetting who) has done specific USB drivers using 3 cogs to do bluetooth, etc. So I think we have an opportunity to do USB OTG, uncompliant, but working, without taking all the props resources.

TonyWaite

Thank you for your advice, which has given me a lot to think about as usual!

Regards,

T o n y