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Welcome to the Altair 8800 emulator repo. If you're interested in retrocomputing, software development, AI, cloud services, and climate monitoring you've arrived at the right repo.
The Altair 8800 kick-started the personal computer revolution. Microsoft's first product was Altair BASIC written for the Altair 8800 by Bill Gates and Paul Allen. At the time, Altair BASIC was a huge step forward as it allowed people to write programs using a high-level programming language.
The Altair project can run standalone and is a fantastic safe way to explore machine-level programming, Intel 8080 Assembly programming, along with C and BASIC development.
This is version 2 of the Azure Sphere Cloud Enabled Altair 8800 and shares the same code base as the Cloud-Enabled Altair 8800 Emulator project that runs on Windows, Linux, macOS, and Raspberry Pi.
The main differences in version 2 are:
- The web terminal now connects over WebSockets. This reduces the solution complexity and allows a local connection from the web terminal the the Azure Sphere device running the Altair emulator.
- There are two mutable storage options for the Altair emulator on Azure Sphere. Either SD Card or 100kB of transient storage provided by the real-time difference disk service.
- Greater focus on the Altair developer experience. There are more examples across BASIC, C, and Assembly programming languages with richer access to climate data and timing services.
- Integration with cloud based AI services, notably Anomaly Detection API. This enables the opportunity to explore AI services using climate data.
- Significant expansion of Intel 8088 IO ports allow for access to climate, timing and publishing services.
- The Azure Sphere specific documentation can be found on this Wiki. Navigate the wiki sidebar documentation starting from the Install Azure Sphere developer tools page.
- The main project documentation is maintained at cloud-enabled Altair 8800 emulator wiki.
- All the source code is provided under an MIT License, and contributions are very welcome.
The Altair emulator is supported on Azure Sphere devices from Avnet and Seeed Studio. If an Azure Sphere device is paired with the Altair front panel kit or the Mikroe Altair Retro Click, the Altair address and data bus activity is displayed.
| Azure Sphere with the Altair front panel kit | MikroE Retro Click |
|---|---|
 |
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Starting from the bottom left and moving up and then to the right.
- POSIX Compatible OS:. The Altair 8800 emulator runs on POSIX compatible operating systems, including Linux, macOS, Windows WSL 2, and Raspberry Pi OS.
- WebSocket & Azure IoT C: These communication libraries connect the Altair emulator to the web terminal and cloud services. The Altair terminal IO messages are routed over WebSockets, and the Azure IoT C SDK connects the Altair to Azure IoT Central.
- libuv library: The Altair coordinates activities on the main thread using the uvlib library event loop services.
- EdgeDevX: This library simplifies access to Azure IoT services, provides event-timer services, along with several useful utilities.
- Terminal IO & Cloud Services: The Intel 8080 CPU provides 256 input ports and 256 output ports. The Intel 8080 ports were used to integrate peripherals such as disk drives, printers, and modems. However, for the Altair emulator, these ports are used to integrate communications and cloud services. Terminal input and output ports are routed over WebSockets, other ports are used for timing services, access to weather and pollution data, plus Azure IoT services.
- Intel 8080 emulator: This is an open-source software implementation of the Intel 8080 CPU. The Intel 8080 emulator executes Intel 8080 applications including the CP/M operating system, compilers, apps, and games.
- CPU Monitor: The CPU monitor implements the virtual Altair front panel, along with memory disassembler, tracer, and Altair emulator reset.
- CP/M: CP/M originally stood for Control Program/Monitor. Later, CP/M became known as Control Program for Microcomputers. It was a mass-market operating system created in 1974 for Intel 8080/85-based microcomputers by Gary Kildall of Digital Research, Inc.
- Programming languages: Included on the main disk image are the Microsoft BASIC interpreter, the BDS C compiler, and the Intel and Microsoft assemblers and linkers.
- Altair BASIC: By default the Altair emulator boots CP/M, but it is easy to boot the original Altair BASIC program.
- Altair Web Terminal: Provides a web-browser hosted Altair terminal. The web terminal is built using the Xterm library. Xterm.js provides a web browser-hosted terminal, a WebSocket integrates Xterm with the Altair emulator.
- Open Weather Map: Open Weather Map provides planet-scale weather and pollution data services. Open Weather Map provides free access to weather and pollution data by geographic location.
- Azure IoT Central: Azure IoT Central is a customizable cloud-based Internet of Things (IoT) application platform. You can report, analyze, and export IoT data.
The Intel 8080 CPU can address up to 256 input ports and 256 output ports; allowing for virtually unlimited system expansion. Access to the ports is via the IN and OUT Intel 8080 CPU instructions.
The Altair emulator uses Intel 8080 IO ports to provide time services, true random numbers, and access to cloud services.
- You can access Intel 8080 IO ports from BASIC, C, Assembly programming languages, and directly using Intel 8080 opcodes. See Using Intel 8080 Input Output ports.
- The Intel 8080 software-enabled IO ports are implemented in the io_ports.c file.
- You can extend the Altair 8800 by adding additional IO port functions, for example, integrating machine learning capabilities.
The following tables shows output port numbers and port data values. Typically, calling an output port will load data to be read via an input port.
| Port | Port data | Loads |
|---|---|---|
| 30 | 0-255 | Set timer period in seconds |
| 33 | ASCII | CopyX filename |
| 41 | 0 | System tick count |
| 42 | 0 | Current UTC date and time |
| 43 | 0 | Current local date and time |
| 44 | 0 | Random number seed between -32000 and 32000 |
| Port | Port data | Loads |
|---|---|---|
| 34 | 0 | "Celsius" string literal |
| 34 | 1 | "Millibar" string literal |
| 34 | 2 | "Humidity %" string literal |
| 34 | 3 | "Wind km/h" string literal |
| 34 | 4 | "Wind degrees" string literal |
| 34 | 5 | "Observation" string literal |
| 35 | 0 | Temperature (Note 1) |
| 35 | 1 | Pressure (Note 1) |
| 35 | 2 | Relative humidity (Note 1) |
| 35 | 3 | Wind speed (Note 1) |
| 35 | 4 | Wind direction (Note 1) |
| 35 | 5 | Weather observation (Note 1) |
| Port | Port data | Loads |
|---|---|---|
| 36 | 0 | "Latitude" string literal |
| 36 | 1 | "Longitude" string literal |
| 36 | 2 | "Longitude" string literal |
| 36 | 3 | "City" string literal |
| 37 | 0 | Latitude (Note 2) |
| 37 | 1 | Longitude (Note 2) |
| 37 | 2 | Country name (Note 2) |
| 37 | 3 | City name (Note 2) |
| Port | Port data | Loads |
|---|---|---|
| 38 | 0 | "AQI(CAQI)" string literal |
| 38 | 1 | "CO" string literal |
| 38 | 2 | "NO" string literal |
| 38 | 3 | "NO2" string literal |
| 38 | 4 | "O3" string literal |
| 38 | 5 | "SO2" string literal |
| 38 | 6 | "NH3" string literal |
| 38 | 7 | "PM2.5" string literal |
| 38 | 8 | "PM1.0" string literal |
| 39 | 0 | Air quality index (Note 1) |
| 39 | 1 | Carbon monoxide level (Note 1) |
| 39 | 2 | Nitrogen monoxide level (Note 1) |
| 39 | 3 | Nitrogen dioxide level (Note 1) |
| 39 | 4 | Ozone level (Note 1) |
| 39 | 5 | Sulphur dioxide level (Note 1) |
| 39 | 6 | Ammonia level (Note 1) |
| 39 | 7 | Particulate matter 2.5 level (Note 1) |
| 39 | 8 | Particulate matter 1.0 level (Note 1) |
| Port | Port data | Loads |
|---|---|---|
| 31 | ASCII | Publish JSON to IoT Hub/Central (Max 256 characters) (Note 3) |
| 32 | 0 | Publish weather and pollution data to IoT Hub/Central (Note 3) |
| Port | Port data | Loads |
|---|---|---|
| 60 | 1 or 0 | Turn Red LED on or off |
| 61 | 1 or 0 | Turn Green LED on or off |
| 62 | 1 or 0 | Turn Blue LED on or off |
| 63 | 0 | Loads onboard temperature |
| 63 | 1 | Loads onboard pressure |
Typically, input ports will read data loaded by an output port.
| Port | Description |
|---|---|
| 30 | Query timer status. Enabled or expired (true or false) |
| 31 | Query publish json pending status. Enabled or expired (true or false) |
| 32 | Query publish weather pending status. Enabled or expired (true or false) |
| 33 | CopyX end-of-file (true or false) |
| 200 | Read loaded byte stream |
| 201 | Read CopyX file stream |
Notes.
- Requires an Open Weather Map API Key, and an active internet connection.
- Requires an active internet connection to call the geojs.io web service.
- Requires an active internet connection and a free or paid tier or Azure IoT Central.
The following code snippets use the Intel 8080 IO ports. The code samples included on the CP/M boot disk expand on these snippets.
The following assembly code demonstrates the use of the Intel 8080 IO port 30 timer. This is a snippet of the sleep.asm sample included on drive A: of the Altair emulator.
ORG 0100H ;CP/M base of TPA (transient program area)
MVI A,2 ;Move 2 to the accumulator to set a 2 second delay
OUT 30 ;Start timer
LOOP: IN 30 ;Get delay timer state into the accumulator
CPI 00H ;If accumulator equal to 0 then timer has expired
JZ BACK ;Jump on zero
JMP LOOP
BACK: RETThe following C code demonstrates the use of the Intel 8080 IO port 30 timer. This is a snippet of the hw.c sample included on drive A: of the Altair emulator.
outp(30,1); /* Enable delay for 1 second */
while(inp(30)); /* Wait for delay to expire */The following BASIC code demonstrates the use of the Intel 8080 IO port 30 timer. This is a snippet of the COUNT.BAS sample included on drive A: of the Altair emulator.
900 REM This sleep subroutine sleeps or delays for 1 second
1000 OUT 30, 1
1100 WAIT 30, 1, 1
1200 RETURNThe following BASIC code demonstrates the use of Intel 8080 output port 35 to load the current temperature, and input port to read the temperature. This is a snippet of the WEATHER.BAS sample included on drive A: of the Altair emulator.
500 PORT = 34 : REM Set the output port number
510 PDATA = 0 : REM Set the port data value to 0 for temperature
520 GOSUB 4800 : REM Loads the temperature and then reads the temperature string
530 PRINT RSTRING$
540 END
4800 REM SUBROUTINE READS STRING DATA FROM PORT UNTIL NULL CHARACTER
4900 OUT PORT, PDATA
5000 RSTRING$ = ""
5100 C=INP(200) : REM Read the temperature character by character until NULL returned
5200 IF C = 0 THEN RETURN
5300 RSTRING$ = RSTRING$ + CHR$(C)
5400 GOTO 5100