virtmem: easily extend your memory

[-Rick-]

Hello all,

virtmem is an Arduino (and Teensyduino!) library that makes it easy to extend the limited RAM available on microcontrollers with 'virtual memory'. To do so, virtmem provides a simple interface to use external memory sources such as an SD card or SPI RAM chip which resembles working with 'regular' memory.

Some of its main features are:

• Extend the available memory with kilobytes, megabytes or even gigabytes
• Supports SPI RAM (23LC series from Microchip), SD cards and RAM from a computer connected through serial
• Easy C++ interface that closely resembles regular data access
• Memory page system to speed up access to virtual memory
• New memory interfaces can be added easily

And a small demonstration that uses an SD card as memory source:

#include <Arduino.h>
#include <SdFat.h>
#include <virtmem.h>
#include <alloc/sd_alloc.h>

// Simplify virtmem usage
using namespace virtmem;

// Create virtual a memory allocator that uses SD card (with FAT filesystem) as virtual memory pool
// The default memory pool size (1 MB) is used.
SDVAlloc valloc;

SdFat sd;

struct MyStruct { int x, y; };

void setup()
{
    // Initialize SdFatlib
    if (!sd.begin(9, SPI_FULL_SPEED))
        sd.initErrorHalt();

    valloc.start(); // Always call this to initialize the allocator before using it

    // Allocate a char buffer of 10000 bytes in virtual memory and store the address to a virtual pointer
    VPtr<char, SDVAlloc> str = valloc.alloc<char>(10000);

    // Set the first 1000 bytes to 'A'
    memset(str, 'A', 1000);

    // array access
    str[1] = 'B';

    // Own types (structs/classes) also work.
    VPtr<MyStruct, SDVAlloc> ms = valloc.alloc<MyStruct>(); // alloc call without parameters: use automatic size deduction
    ms->x = 5;
    ms->y = 15;
}

void loop()
{
    // ...
}

The project is hosted on github: https://github.com/rhelmus/virtmem
A detailed manual with more info can be found here: http://rhelmus.github.io/virtmem/index.html

Most of the development was done on Teensy 3.X boards. This is the first release, but already pretty feature complete. Nevertheless, any feedback (questions, suggestions, bugs etc) is welcome!

[duff]

Hmmm, I wonder if this would be useful with OTA? Have you tried loading the binary of a sketch into this virtual memory, or am I totally off base here?

[Cosford]

Huh. Very cool. Will have a play.
One particular application springs to mind because I know it's something some of the guys here struggle with a tidy solution for; audio delays.

Thanks for sharing!

[WMXZ]

One particular application springs to mind because I know it's something some of the guys here struggle with a tidy solution for; audio delays.

For audio delays, you may consider also Frank's Memoryboard. See also Paul's 9s delay demo, e.g.
https://forum.pjrc.com/threads/29276...ll=1#post80049

[Cosford]

Yeah, I'm aware of that solution. Just wondered whether this could potentially provide an alternate solution for those interested in it. (Not something I need personally).

[-Rick-]

Thanks for the feedback!

Hmmm, I wonder if this would be useful with OTA? Have you tried loading the binary of a sketch into this virtual memory, or am I totally off base here?

I am not so familiar with this topic. I think the binary instructions could be put in virtual memory. You would still need to find a way to properly execute the chunks.

Huh. Very cool. Will have a play.
One particular application springs to mind because I know it's something some of the guys here struggle with a tidy solution for; audio delays.

Thanks for sharing!

Yes, I guess virtmem could bring a nice alternative to that. What kind of speed requirements are we talking about?