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X86 Products


pmEasy®

Protected Mode Environment

pmEasy offers a middle-ground between Windows- or Linux-based systems and real-time systems which are burned into EPROM or flash.

Like a desktop OS, pmEasy starts in real-mode, switches the processor to protected mode, loads the application into RAM, and starts it running. The application is in the form of a relocatable exe file. Unlike desktop OS's, pmEasy is designed to support hard real-time requirements. It is also compact and fast.

Unlike DOS-extenders, which have also been used for embedded systems, pmEasy does not greatly increase interrupt latency nor task switching time.

Hence, pmEasy is appropriate for embedded systems which have some form of disk, and for which locating and burning code into ROM is not appropriate or not desired. (e.g. The application is large and complex or is in a state of flux.)


Application Loading

An important benefit of pmEasy is that it avoids the complexity of using a linker/locator. There is no worrying about addresses, descriptor tables, or how to start from system reset. The application is linked with the native linker of the Borland or Microsoft C/C++ compiler and pmEasy loads the resulting exe file from disk into RAM.

The following devices are supported:

• Floppy Disk (FAT12)
• IDE Hard Disk (FAT16, FAT32)
• LS-120
• Iomega Zip
• CDROM (ATAPI)
• M-Systems DiskOnChip® Flash Disk
• DOS devices (see below)

There are two versions of pmEasy: (1) pmEasy16 for 16-bit, segmented protected mode, and (2) pmEasy32 for 32-bit, flat protected mode.

pmEasy16 is particularly advantageous when upgrading from DOS. It loads exe files in the NE (New Executable) format, as used by Windows. This type of exe file is generated using the same compiler and linker as for real mode, but with the PROTMODE module statement.

pmEasy32 loads exe files in the PE (Portable Executable) format used by Windows NT. The exe file is a console-mode executable generated by a 32-bit, flat-mode compiler and linker, such as Borland C++ or Visual C++.


Loading pmEasy

pmEasy can operate with or without DOS present. It can be loaded and run from the DOS prompt. When running from DOS, the drive letter and file name of the application program can be specified on the pmEasy command line (e.g. C:> pme c:myapp.exe). Also, pmEasy can be bound to the application so that there is a single executable (e.g. C:> myapp). The ability to run from DOS is especially convenient during develop­ment. It is also useful for targets shipping with DOS. In such systems, pmEasy will exit cleanly back to DOS when the application is stopped.

For systems with only a BIOS, pmEasy can be bootloaded from disk. The exe2bin (or equivalent) utility is used to generate a binary file for pmEasy. A utility is included with pmEasy to replace the disk boot sector in order to load the binary image of pmEasy.  pmEasy, in turn, loads the application. DOS is not required in this process.

pmEasy does not depend upon DOS or upon BIOS to run. These are simply convenient ways to start it and to do hardware initialization. It is possible to locate pmEasy to run from ROM. In this case, the application code must include its own hardware initialization code — something the BIOS would normally take care of.

pmEasy includes a simple disk reader and drivers for loading from all of the devices listed on page 1. Any combination of drivers can be selected from the makefile used to make pmEasy. Typically, only one driver would be linked, but if the system has more than one type of drive, as many drivers as necessary may be linked to pmEasy.

Note: Device drivers included with pmEasy are modified for pmEasy and provided in object form only. They are not suitable for use with smxFile.

In addition, a special version of the disk reader is provided that uses DOS int 21H calls and DPMI 300H to load the program. This provides the ability to load from any device that has a DOS device driver, if DOS is present!

Sample applications and makefiles are provided. (If also using SMX, the Protosystem is the sample application.)


Protected Mode

When pmEasy is started, it initially runs in real mode. It is usually a DOS-style, real-mode exe, unless it is being bootloaded, in which case it is a binary file or unless it is being run from ROM, in which case it is a binary image. pmEasy sets up protected mode structures such as the global descriptor table (gdt) and the interrupt descriptor table (idt). It also hooks default exception handlers to the processor exception interrupt levels. Then pmEasy switches the 386-or-higher processor into protected mode. Next it loads the application into RAM and starts it running.

While the application is running, pmEasy provides a reduced DPMI[1] server. Services such as heap (i.e. RAM) allocation, local descriptor table management, and interrupt descriptor table management are provided.

The heap can be configured to span multiple, disjoint areas of memory using a simple table (see Flexible Heap, below). Also, some specialty functions are provided, such as DPMI 300H. This function allows invoking a real-mode software interrupt (e.g. int 21H (DOS) or int 10H (BIOS)) after pmEasy has switched to protected mode. This function is for use during initialization, such as to initialize a display controller to a particular graphics mode. (This ability can be a real life saver when the manufacturer of the display or other hardware provides only a real mode (e.g. BIOS int 10H) driver.)


EXE Debugging

For debugging the application code, pmScope and pmLoc are used. pmLoc is used to generate the debug symbolics for pmScope from the exe file. A special version of pmEasy that has been linked with the debug monitor, pmMon, is run on the target platform. It can be loaded the usual ways and, in turn, it loads the application from disk. Meanwhile, the user loads the symbols into the debugger on the host. When the exe load is complete, debugging can begin.

Another option is to use the VisualProbe debugger. This requires locating the application with Link & Locate 386. With this approach, Embedded pmEasy is used during debugging. For normal execution, the application is built as an exe, as usual. For smx users, this option is provided in the Protosystem makefile.


Flexible Heap

pmEasy 's heap can span multiple blocks of available RAM. The user specifies a table of starting and ending addresses of free memory blocks and pmEasy initializes the heap accordingly. This allows using all available RAM. For example, memory from the top of pmEasy to 640K and above 1M can be included in the heap.

Automatic memory sizing is also supported. This is accomplished by specifying a special value for the ending address of the last region in the table. pmEasy searches for the end of RAM, in user-specified increments, and sizes this block of heap as large as possible. This is useful for systems that are shipped with variable amounts of RAM or which may be upgraded in the field.


OMF Debugging

For those who prefer to use a debugger that accepts only omf files (e.g. VisualProbe), a reduced version of pmEasy called Embedded pmEasy is included in the pmEasy package.See the smx86 brochure for discussion of this option. Basically, it permits debugging with omf files, but running with exe files.


Hex Loader

The exe file loader in pmEasy can be replaced with a hex file loader. Hex files are one type of file produced by linker/locators. A hex file is not relocatable. Also a hex file is typically twice as large as the corresponding exe file. However, since each record is check-sum protected, a hex file is more secure for downloading via LAN or serial link.

The hex file loader can also be used with Embedded pmEasy to permit faster application loading into the target, during debugging. (Either via LAN to target hard drive or via floppy to target floppy drive.)

• 386 or higher
• pmEasy 16 supports 16-bit PM applications
• pmEasy 32 supports 32-bit PM applications
• Enters protected mode and stays there — no switching back and forth into and out of real or V86 mode, which severely hurts performance.
• Subset of DPMI services, compatible with DPMI specification version 1.0 (Intel Order No. 240977-001)
• ROM’able, bootable, or DOS loadable
• Standard pmEasy loads from many types of disk with the provided drivers. Other disks can be read using DOS file i/o, if DOS present.
• Will exit cleanly to DOS, if started from DOS
• Allocates available memory below and above 1MB (uses free memory table created by user)
• Standard pmEasy supports pmScope debugger
• Embedded pmEasy supports VisualProbe debugger
• Low-cost PC tool integration already done
• Built with MASM and Microsoft 16-bit C compiler, both available cheaply.
• Supports both PC and non-PC compatible targets
• Simply designed, easy to understand, well-structured code
• Source code is provided. Promotes understanding and allows customization
• Compatible with the SMX product family
• Works with or without SMX.

1. DOS Protected Mode Interface - an API developed by Intel and others
2. Sizes are with standard settings. Disabling video output and other features reduces pmEasy size significantly. Also some features use buffers of configurable size. If memory is tight, please contact us to determine an accurate size for the exact configuration you plan to use.
3. Size of pmEasy32, including PE loader and disk reader. pmEasy16 + NE loader size is similar. pmEasy is about 2K smaller with hex loader instead of PE loader.

• Access the manual.
• Try a free evaluation kit.