Sunday, March 06, 2016

SIMPL meet SIMPLEX - Part 1 - Putting it Together

SIMPLEX - the EXtended Version Of SIMPL

So I took SIMPL running on a LaunchPad, and added a 23K256 RAM chip with 6 jumper wires and a 10K resistor:

Overall View

I'm probably infringing a whole bunch of trademarks but the EXtended version of SIMPL which uses the EXternal SPI RAM will be called SIMPLEX. 

Now that's what I call subtle! With a touch of irony.

With the RAM expansion comes the need to examine and modify its contents, and so I have written a bit of code to allow the contends of the RAM to be dumped to the screen in both decimal and hexadecimal formats, with ASCII equivalent in a separate column.

Whilst the SIMPL kernel code fits into 2Kbytes - and as such may be considered as a smart interactive bootloader, the high level routines to manipulate the RAM extend this limit quite considerably.

The code I have produced is "quick and dirty"  C, and I am sure it could be written more succinctly at a later date.

The decimal-dump D and hex-dump H commands are the start of a new group of high level commands to handle external memory, editing etc.

30 or so years ago, "monitor" programs were common place on the early 8-bit micros. They allowed for the direct editing of data within the RAM space of the memory map - and were a means of entering programs - one hex byte at a time.  It was a welcome step up from toggle switches!

The "Editor"  will use the first 8 commands of the User Words, signified by letters A through to H, each representing a high level operation.  One allocation of these is as follows:

A           Assemble
B           Block
C           Compile
D           Decimal Dump
E           Edit
F           File
G          Go   (execute from RAM)
H          Hex Dump

Several of these are really just place-holders for yet to be written command functionality.

The first task of being able to examine the RAM contents has been undertaken, now its time to start looking at the process of getting code into the RAM area and then executing it from RAM.

The 23K256 has a page size of 32 bytes, which is a useful size for a phrase of SIMPL code.

Looking at the Block B and File F commands above, the block command can be used to manipulate the memory 32 bytes at a time - effectively a line of SIMPL code, whilst the File command can be used for handling multiple blocks. 

The hexadecimal conversion is used both for 2 digit (<= 255) and 4-digit (256 <=  x <= 65535) conversions.

I have includes a SIMPL primitive   $  which takes an integer x and converts it to either 2 digit or 4 digit hex.

The dump formats make use of the modern wider terminal screen.  1K of RAM can be dumped to a single screen - of 32 lines of 32  hex bytes.

The Hex -Dump as it appears on Termite Screen. 1K bytes of RAM data shown per screen

I have put the code for SIMPLEX_1 on this Github Gist  Please note that the UART is running at a non-standard 100Kbaud instead of 115200.  This is to be investigated later. 

In the next post, I'll look at more RAM operations plus actually running SIMPL code out of the external SPI RAM.

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