mycontroller – DMA

This is part of a project to build a complete, functional, extremely basic microcontroller. It is built using multimedia logic.

This section is a simulated very simplified DMA.

Example Run

The test of writing back and forth bytes seems to work.

Also, the example from the lab specification seems to work. Namely:

Download:

• Select head 1, track 2, sector 3, block 4 on the disk.
• Select address AB on the RAM.
• Select 6 bytes to transfer.
• Select download.
• Disable the master clear.
• Hit the transfer button. The yellow download LED should illuminate.
• Hit the clock at least 7 times. Your transfer should stop after the 6th cycle, illuminate the green completion LED, and deactivate the yellow download LED.
• You should see 6 different bytes transfer from disk blocks 4 through 9 from head 1, track 2, sector 3 to RAM addresses AB through B0, respectively. The particular bytes depend on how you organized the address space on your “disk.”

Upload:

• Select head 2, track 3, sector 4, block 5 on the disk.
• Select address AC on the RAM.
• Select 2 bytes to transfer.
• Select upload.
• Hit the transfer button. The yellow upload LED should illuminate.
• Hit the clock at least 3 times. Your transfer should stop after the 2nd cycle, illuminate the green completion LED, and deactivate the yellow upload LED.
• You should see 2 bytes transfer from RAM addresses AC and AD to disk blocks 5 and 6 on head 2, track 3, sector 4.
• These should be the second and third bytes you saw in the download example.

Known Issues

You can’t have reads/writes across different tracks or heads, which will produce (perhaps to the user) unexpected results, overwriting the same sectors rather than proceeding to the next track. In short, reading/writing across tracks requires multiple reads/writes.

I made a conscious decision to not worry about the clock wrapping around at this point. If the clock does wrap around, it may screw stuff up.

Screen Shots

Here is a link to the source.