Wait states 1

Wait states

Jan

8

2012

My recent order of boards from BatchPCB got lost somewhere on its way. I am not sure if it was lost by USPS, at customs or at my local post office here in Warsaw, but the fact is I am still waiting for a new memory and UARTs boards. BatchPCB is re-doing my order now ...
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Design · Design - control

IDE interface with RTC 4

IDE interface with RTC

Dec

4

2011

There are two things in my design still missing to declare completion of basic hardware – real-time clock and IDE interface. Hence, my recent project activities concentrated on these two elements. RTC and IDE will occupy a dedicated expansion board and will be built in a way to keep hardware complexity to the minimum. RTC ...
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Design - I/O

Memory system update

Memory system update

Oct

29

2011

My memory system has recently undergone an update to hardware design. Originally I planned and implemented four memory bank registers – two for lower and upper 32kB of code, and two for lower and upper 32kB of data (see this post for details). With hardware able to address maximum of 128 banks via 22-bit address ...
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Design · Design - memory

Assembler and instruction set update 2

Jul

31

2011

I am slowly progressing on my simplistic OS/Monitor development. It is only a little fun, mainly because I do not have a functional simulator (i.e. emulator) of the computer and I have to test every bit of assembly code on real hardware. For that I have to constantly switch from Linux (where my development toolchain ...
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Design - ISA · Software

More bugs

More bugs

Jun

14

2011

Recent exercises with UART revealed two interesting bugs in my design. Both problems were resolved and I am documenting them here for dairy keeping. Implicit memory reads It is something I have discovered only now, playing with real devices attached to the CPU’s expansion bus. The problem is related to side effects of implicitly reading ...
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Design · Design - control

UARTs board draft schematics

UARTs board draft schematics

May

7

2011

I completed the initial revision of UARTs board schematics last night. Both 16550 UART chips and MAX232 level converters were new to me, so the task took several hours. Unlike with simple TTL chips, this time I really had to study the datasheets carefully to understand what all those pins do. I am only going ...
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Design - I/O