ILI948x_t41_p - a parallel display driver for Teensy 4.1

[Rezo]

Been playing around with it - got a partial read to work and it’s writing some odd stuff to the display.
The issue is the bit shifting from the data point to the buffers - my skills with bitwise operators are somewhat limited and while I know exactly how each operator works, I just can’t get it to play right. Even chatGPT is way off at this stuff many times.

Anyways, will try debug more with the logic analyzer when I get a chance!

[DutchMaker]

Let me know if I can help with the bitwise puzzle.
It’s also not my strongest suit but I may get lucky :-D

[Rezo]

Let me know if I can help with the bitwise puzzle.
It’s also not my strongest suit but I may get lucky :-D

Sorry for the late reply, was on vacation the whole week!

I pushed an update that semi works - you can try it out, although something broke my 9486 and I can no longer test on the bench.

Here is the bit shifting logic:
The FlexIO buffer is 32 bits long
We are using bits 0,1,2,3 and 6,7,8 and 9 for the data (same pins as well)

So when writing a command (8 bits in length) we need to shift the upper 4 bits to FlexIO bits 0-3 and the lower 8 bits to FlexIO bits 6-9
When writing pixel data (16 bits in length) we need to use the same approach as the command, but we need to split the 16 bit integer into two 8 bit integers - the lower byte and the upper byte

When reading, we do the opposite, we read bits 0-3 from FlexIO and push them into an 8 bit integer, and then we read bits 6-9 from FlexIO and write them into the 8 bit integer from bit #4.

So in theory this is all fairly simple, but I just can't get it to work properly for some reason.

[DutchMaker]

Thanks for the explanation.
I will try to get it to work early next week and share my findings.

[DutchMaker]

Sorry for the late reply, was on vacation the whole week!

I pushed an update that semi works - you can try it out, although something broke my 9486 and I can no longer test on the bench.

Here is the bit shifting logic:
The FlexIO buffer is 32 bits long
We are using bits 0,1,2,3 and 6,7,8 and 9 for the data (same pins as well)

So when writing a command (8 bits in length) we need to shift the upper 4 bits to FlexIO bits 0-3 and the lower 8 bits to FlexIO bits 6-9
When writing pixel data (16 bits in length) we need to use the same approach as the command, but we need to split the 16 bit integer into two 8 bit integers - the lower byte and the upper byte

When reading, we do the opposite, we read bits 0-3 from FlexIO and push them into an 8 bit integer, and then we read bits 6-9 from FlexIO and write them into the 8 bit integer from bit #4.

So in theory this is all fairly simple, but I just can't get it to work properly for some reason.

I'm gonna take a look at this but wanted to check if I understand the goal correctly.
Let's assume command = 1101 1001

Then the high nibble is 1101
The low nibble is 1001

Must the FlexIO integer then be:

0000 0010 0100 1101

Just want to know sure I have the bit positions correct before I work on solving the bit shifting.
If my example is off, then please supply values for the correct example and I'll try to fix it.

[Rezo]

If the command value is 1101 1001 then FlexIO shifter buffer needs to receive 0000 0011 0100 1001
Basically between the 4 high bits and 4 low bits we insert two empty bits as can be seen between the highlighted bits above

[DutchMaker]

Fixed the shifting and created a pull request.
Still nothing on the screen though...

[Rezo]

Maybe the shift into the FlexIO buffer needs to be the opposite way around
Eg shift 4 bits in from bit 22 to bit 26 and then another 4 bits from bit 28-31