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87 lines
4.1 KiB
Markdown
87 lines
4.1 KiB
Markdown
---
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title: Software Design
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description: "TommyPROM Arduino 28C256 programmer software design"
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has_children: false
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nav_order: 3
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---
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# Software Design
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The software is designed around several major blocks and classes. The code has been
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broken out into individual files to make it easy to extend the hardware support to
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additional EPROM and EEPROM families. See the
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[Adding Chip Families](../extending) page for details on suggested hardware and software
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changes needed.
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## CommandStatus class
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The CommandStatus class stores the execution status of the previous command. It allows
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the status to be saved (and recalled using the / command) instead of just printing the
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status at the completion of the command. This was important for debugging XMODEM
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problems, because the error messages would get eaten as part of the transfer. The class
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has utility beyond XMODEM because it includes formatting that relieves each command from
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having to build parameterized error messages with multiple print calls.
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## Xmodem class
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The Xmodem class implements the communications protocols needed to do XMODEM CRC transmit
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and receive. It calls directly into the PROM read and write code, to the complete files
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are never stored during the transfer.
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## CLI code and command implementation
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This code parses input commands and parameters and executes the commands.
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A compile-time switch in Configure.h enables additional debug commands that are not needed
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in normal operation, but are very useful to verify proper operation of the hardware.
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## PromDevice class
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The PromDevice class and its subclasses encapsulate all of the communication between the
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Arduino and the target PROM device.
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To meet the timing requirements for block writes and 28C chip unlocking, the PromDevice
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class accesses the shift registers and data bus using direct port writes instead of 8
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individual pin accesses. This greatly increases performance, but it makes the code
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dependent on the particular flavor of Arduino being used. The code supports the Uno,
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Nano, and Boarduino versions of Arduino hardware or any other variant that uses that same
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mapping of ATMega ports to I/O pins. To support a different Arduino board, either change
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the pins used to match the mapping in the software, or change the hardware-specific code
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in PromDevice.cpp and PromAddressDriver.cpp.
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The PromDevice class contains common code used by all devices, including the block write
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code that will break a large write request into a set of properly-aligned smaller blocks
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for devices that support block writing, or a sequence of individual byte writes for
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devices that do not.
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Subclasses of the PromDevice class provide the device-specific code. To accommodate the
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limited memory footprint of the Arduino, only a single subclass will be compiled into the
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final code. This is controlled via switches in the Configure.h file.
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The device-specific subclasses are described below. Each class provides pin definitions,
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byte read, byte burn, and optional block burn code that is specific to the timing of the
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chip. They also supply a SetAddress method that either calls the built-in code for the
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shift register hardware or provides device-specific address code.
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### PromDevice28C class
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Although the existing code is specific to the 28C256, the constructor has parameters that
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easily support other chips. The current design has been used to read other chips,
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including 2764 and 29c040 EPROMs.
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The 28C code supports fast block writes, allowing a 32K byte chip to be programmed in just
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a few seconds.
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### PromDevice8755A class
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The PromDevice8755A class provides the byte read and byte write code, as well as
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SetAddress code that accommodates the ALE used on this chip. The byte write code controls
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the Vdd switching hardware that toggles the Vdd pin between the normal 5V value and the
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25V programming pulse.
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### PromAddressDriver class
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Although not actually a subclass of PromDevice, this contains the code to drive the shift
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registers that provide the address lines. If this hardware is used, the PromDeviceXX class
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can call this code to implement the SetAddress methods.
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