A project log for Trinity Core and Net

A 32 Bit Variable Length Instruction Set Core and Transputer Like Comms Network

andre-powellAndre Powell 11/04/2019 at 23:160 Comments

From the previous success of getting the RS232 to work at 9600 Baud the next incremental step is to get it to work at 115200 Baud.

This has now been done successfully.

The reason for getting this to work is to see if I can create a real time 'large' display of 80 characters by at least 30 lines.
To do this we need to send the contents of what is needed to be displayed plus the command codes to send the cursor around a monitor. Carriage Return and Line Feed will get the cursor down and to the left of the screen. The cursor needs to get back to the home position. I understand that the cursor can be sent up n lines using VT100 codes which takesfour characters.
This display needs to be refreshed within 400 ms. This is the Doherty Threshold as made famous in 'Halt and Catch Fire'. By ensuring that all the characters are sent in this time we can guarrantee that the Doherty Threshold is met.

The plan is to initially confirm the screen control via writing the appropriate characters.
Once this has been confirmed the Screen Engine will be written.
An area of memory will represent the screen, the Screen Engine will transfer the memory contents to a Tx Uart. It will then pass the control charcters.
For a 40 line by 80 character display then 3200 printing characters need to be sent. Along with these we have 40 Carriage Returns, 40 Line Feeds and then finally four characters to send the cursor back home. So we are looking at 3284 characters. 
If we are to keep within the Doherty Threshold at 115200 Baud then we can send 4602 characters, so 3284 characters is well within this limit.
As to response time of the machine that will be up to the software to be written, however by making the Screen Engine handle the display the Software can get on with the job working out what is needed to be displayed the problem is reduced.