ryanvarick.com - Analog Hardware Abstraction Layer

The Case for an Analog Hardware Abstraction Layer

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This too is incomplete; I'll update eventually. :-)

TODO:

Motivate the need for a HAL
Discuss the proposal (below)
Add the class-based discussion with Drew (via AIM)
Add JAVA class proposal
Toolkit Driver Architecture

Axes of Consideration

Substrate - silicon, foam, jell-o
Hardware version - EAC, uEAC, simulator
Communication medium - Ethernet, serial, virtual

Existing HAL

Copied from an email to Drew.

I've got a few minutes, so I thought I'd conjecture about the proposed HAL for JEAC. I have a simple five-layer interface for my toolkit under source control for a different project: http://home.ryanvarick.com/svn/eac-toolkit/trunk/hardware.pm

The comments in there may be useful if you want to look through it. Here's the gist of things:

At the bottom layer is channel communication (serial, Ethernet).

Above that, basic sentence interaction (sending sentences and reading their responses). Successful commands should return the sentence, errors return the FxxxxxZ (or whatever it is). Reading a value involves the DxxxxxxZ sentence, I think. LLAs might be a special case -- returning their values instead of the original sentence... I don't remember.

Above that, we can begin to define useful abstractions, read_ and write_dac, to differentiate between sentence modes. At this level, we can get away from sentences altogether.

Now that we're at the level of individual connections (called DACs), we can define distinct commands -- read, source, sink, etc.

Finally, we have a meta-level, for things like read_sheet, etc.

Here's how my code defines thigns:

#  Abstraction diagram:
#
#   LEVEL   FUNCTION NAME                     LAYER INFORMATION
#   =====   =============                     =================
#
#    (5)    reset_board                       some useful meta functions
#    (5)    get_gradient
#    (5)    report_lla
#    (5)    report_chain
#
#    (4)    read_voltage, write_source        command abstraction layer
#    (4)    read_lla_input, write_sink
#    (4)    read_lla_output, write_lla [*]
#
#    (3)    read_dac, write_dac               basic hardware command layer
#
#    (2)    init_hardware
#    (2)    write_command                     hardware communication layer
#
#    (1)    open/close_socket,
#           open/close_serial port            communication channel layer
#