Write a PS/2 Keyboard Interrupt Service Routine

PS/2 keyboard ISR

IRQ1 signals data available at port 0x60 (scan code) and status in port 0x64. The ISR should read the byte, translate with a table if needed, and buffer it for the main loop. For example, scan code 0x1E is the make code for the 'A' key; 0x9E is the break code with high bit set on older sets.

Minimal ISR flow

nasmCopy
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• Scan code set 1/2/3: Layout differs; PC AT uses set 1
• Shift/ctrl: Track modifier bytes separately from letters
• Controller command: Port 0x64 bit 0 set means output buffer full
• Do not call blocking BIOS from ISR; buffer only

Scan code sets

Set 1 uses make/break with bit 7 set on release; set 2 uses 0xF0 prefix bytes. The 8042 may buffer multiple bytes during fast typing; drain port 0x60 until empty inside the ISR or risk losing edges. Do not translate to ASCII inside the ISR if you use a complex layout table; store raw bytes and translate in the main loop where floating point and division are allowed.

Why for this exercise

You will handle IRQ1, read scan codes from port 0x60, and store them in a ring buffer. This exercise requires PIC EOI and non-blocking work inside the handler.