GWMON-65 is intended to be a simple ROM-type system monitor for systems utilizing processors that are compatible with the MOS 6502, including (but not limited to) R6501 and R6511 systems. It is written in a modular format so that it can be extended for use with specific system hardware with ease. It is being developed and released under the GNU GPLv3 as open source software (see LICENSE in project root for more information).

GWMON-65 is a port of GWMON-80.

The following customizations are available and can be built using make and the contents of the Make Target column.

GWMON-65 is composed of the following components:

• Jump table
• Core monitor, either SM (Small Monitor) or XM (eXtended Monitor)
• Command set(s) and handlers
• I/O modules
• Customizations

The jump table provide consistent entry points to GWMON-65. Vectors are provided at the beginning of the monitor in the form of a jump table. Standard vectors are:

• CSTART at ORG + 0: cold start routine
• WSTART at ORG + 3: warm start routine
• COUT at ORG + 6: output a character to console
• CIN at ORG + 9: wait for and input a character from console

There are two options available for the core monitor: SM (Small Monitor) or XM (eXtended Monitor). Currently, only SM is recommended as XM is still under development. SM has the advantage of being simpler and much smaller: most customizations using SM are 512 bytes or less.

Command sets provide data structures that define commands. The SM and XM standard command sets (scmdstd.inc and xcmdstd.inc, respectively) also provide the default command handlers for those core monitors. Command sets are chainable such that additional commands can be added into a given customization. Command sets are terminated by a "NULL command," which is monitor-specific and should be included after all other command sets.

Handlers provide actual implementation of commands. The core command handlers are defined with their command sets, but additional handlers must be defined separately from their command sets to allow command set chaining.

I/O modules contain the routines necessary to initialize the console I/O device, receive characters from it, and transmit characters to it. They are generic implementations for a given device; for example, r6500uc.inc provides the routines for talking to any system using the built-in serial port on R6500/1 family single-chip microcontrollers.

Customizations tie together vectors, a core monitor, I/O module, and one or more command sets into a machine-specific implementation of GWMON-65. See smr6501q.a65 for an example of a basic customization of the SM for the Glitch Works R6501Q SBC with the standard SM command set. See smosi1.a65 for an example of a customization that requires I/O setup.

If a customization for your system already exists, GWMON-65 can be built using the included Makefile:

make r65x1qsbc

...or by assembling the source directly from the command line. Many customizations build to an Intel HEX file, or platform-specific loadable format.

The Small Monitor (SM) command syntax is as follows:

D XXXX YYYY     Dump memory from XXXX to YYYY
E XXXX          Edit memory starting at XXXX (CTRL+C to end)
G XXXX          GO starting at address 
L               Load an Intel HEX file into memory

CTRL+C may be pressed at any text entry point to cancel the current operation. Hexadecimal inputs are validated, entering a non-hex character will cancel the current operation with an ERROR message.

The SM command processor automatically inserts the spaces after each element. So, to dump memory from 0x0000 to 0x000F you'd type

d0000000f

...and you'd get

>d 0000 000F
0000 : xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx

>

...where the xx fields are the hex representation of the bytes at those addresses.

No returns or spaces are typed in the commands. This is very similar to the NorthStar ROM monitor, most likely because it's about the simplest way to implement. Input is auto-downcased, so you can type entries in either (or even mixed) case.

The E command prompts for a starting address, displays the contents of the memory location, and allows input of a replacement value. Pressing RETURN will leave the current value unchanged and move to the next memory address. Pressing CTRL+C at any time terminates the E command.

G prompts for an address and transfers control to that address. The GWMON-65 warm start address is placed on the stack prior to control transfer, so routines may return to GWMON-65 with a RTS as long as the stack has been preserved.

The Intel HEX loader expects 16-bit addresses. It behaves as an Intel loader should, allowing empty blocks in the middle to be skipped. It will accept either UNIX-style LF endings or DOS/Windows CR/LF endings. The loader will accept an EOF (End of File, 0x01) record or a data record (0x00) with zero length as the terminating condition.

After invoking the loader, paste your Intel HEX file into the terminal or do an ASCII upload (depending on your terminal program).

If input or checksum errors are encountered, an asterisk will be printed on the offending line, and ERROR will be printed after the hex load completes.

The Small Monitor (SM) supports an I/O command set, provided in scmdio.inc and iocmd.inc. This command set provides shorthand I/O read and write for systems with a fixed 256-byte I/O page in the memory map, such as the Glitch Works GW-6502SBC-1. The I/O commands follow GWMON-80 syntax:

I XX            Input from I/O port XX and display as hex
O XX YY         Output to I/O port XX byte YY

IOPAGE must be defined in the customization. For Glitch Works boards, the default I/O page is 0xEF00. When an I or O command is executed, a memory access is made to the I/O page with the low address byte specified in the command (XX above). For example, the command sequence I01 would result in a memory read from 0xEF01.

See smgw6502sbc1.a65 for an example implementation.

Typing make will build all GWMON-65 customizations. Many convert into Intel HEX format or other loadable formats. This project uses the assembler from the CC65 package.