How the Amiga Reads Floppies

17 hours ago

The Amiga floppy controller uses four separate chips instead of a single integrated controller like the NEC765.
Two 8520 CIAs handle control I/O: the odd CIA manages outputs from the drive (disk sensing), and the even CIA manages inputs to the drive (selection, control, stepping).
Gary handles motor control and write data, processing signals from Paula through a NAND gate inverter.
Paula processes read data, performs DMA, and includes a hardware digital PLL for data separation; it does not handle drive selection or motor control.
MFM encoding/decoding is handled in software by the trackdisk.device in Kickstart ROM.
The author found detailed patents for Paula's DPLL (US patent 4780844) and Paula itself (US patent 4829473), revealing hardware-based data separation.
The Amiga's approach is more software-heavy than PC controllers, offering greater flexibility.

IBM i (originally AS/400) is a unique operating system with an integrated Db2 database at the kernel level, treating database and OS as one inseparable unit.
It uses an object-based architecture instead of file-centric, with Single Level Storage (SLS) treating all memory and disk as one flat address space.
The TIMI abstraction layer ensures decades-long backward compatibility, allowing programs from 1990 to run on modern hardware without recompilation.

Intel introduced the 8086 processor in 1978, a 16-bit chip that founded the x86 architecture.
The ALU performs 28 operations including arithmetic, logic, shifts, and BCD adjustments.
Microcode controls the ALU via a two-step process: first configure the ALU, then retrieve the result.

The author built a physical 17x17 matrix of switches with integrated LEDs to simulate Conway's Game of Life, using a microcontroller (AVR128DA64) to control rows and columns.
The LED display uses a multiplexing scheme where each row is active for 1/17th of the time, requiring higher current (150 mA per LED) to maintain brightness, with MOSFETs for row and column switching.
User input is detected by reusing row select lines to ground and sensing switch closures via GPIO pins, with pull-up resistors integrated on the MCU.

A 16-bit serial homebrew CPU was built using only 8 ICs, including memory and clock, achieving Turing completeness.
The CPU uses a single EPROM as both control state machine and 1-bit ALU, with two serial SRAMs and one serial FLASH.
It executes around 12,000 instructions per second at up to 10 MHz, capable of streaming video on a Nokia 5110 LCD at ~10 FPS.

The Disk II controller is a dumb hardware design that offloads low-level disk operations to software, unlike other controllers that provide a standard API.
Steve Wozniak designed the Disk II controller with minimal hardware, using only eight chips and a software-driven approach, enabling cost-effective floppy disk support for the Apple II.
Key challenges solved include byte framing via a state machine and sync bytes, byte encoding using GCR schemes like 6-and-2, sectoring with software signatures like D5 AA 96, and track locating through stepper motor control.

IBM i (originally AS/400) is a unique operating system with an integrated Db2 database at the kernel level, treating database and OS as one inseparable unit.
It uses an object-based architecture instead of file-centric, with Single Level Storage (SLS) treating all memory and disk as one flat address space.
The TIMI abstraction layer ensures decades-long backward compatibility, allowing programs from 1990 to run on modern hardware without recompilation.

Intel introduced the 8086 processor in 1978, a 16-bit chip that founded the x86 architecture.
The ALU performs 28 operations including arithmetic, logic, shifts, and BCD adjustments.
Microcode controls the ALU via a two-step process: first configure the ALU, then retrieve the result.

The author built a physical 17x17 matrix of switches with integrated LEDs to simulate Conway's Game of Life, using a microcontroller (AVR128DA64) to control rows and columns.
The LED display uses a multiplexing scheme where each row is active for 1/17th of the time, requiring higher current (150 mA per LED) to maintain brightness, with MOSFETs for row and column switching.
User input is detected by reusing row select lines to ground and sensing switch closures via GPIO pins, with pull-up resistors integrated on the MCU.

A 16-bit serial homebrew CPU was built using only 8 ICs, including memory and clock, achieving Turing completeness.
The CPU uses a single EPROM as both control state machine and 1-bit ALU, with two serial SRAMs and one serial FLASH.
It executes around 12,000 instructions per second at up to 10 MHz, capable of streaming video on a Nokia 5110 LCD at ~10 FPS.

The Disk II controller is a dumb hardware design that offloads low-level disk operations to software, unlike other controllers that provide a standard API.
Steve Wozniak designed the Disk II controller with minimal hardware, using only eight chips and a software-driven approach, enabling cost-effective floppy disk support for the Apple II.
Key challenges solved include byte framing via a state machine and sync bytes, byte encoding using GCR schemes like 6-and-2, sectoring with software signatures like D5 AA 96, and track locating through stepper motor control.

Hasty Briefsbeta