Looking for suggestion on best way to use 24-bit data received via 32-bit EPI FIFO and uDMA controller

Jeff McDevitt

I am using the EPI interface in GP mode with 24-bit data and 4-bit addresses to read data from an FPGA.. I read it into the FIFO which is set to 32-bits (there is no option for 24-bits). I then use the uDMA to read it into a uint32_t buffer. After that I want to use the lower 24-bits of the uint32_t buffer. Can anyone suggest a quick way to do this? Is there a way to setup the uDMA to only read the lower 24-bits from the NBRFIFO? (I couldn't find one). Or do I have to manually copy the buffer to drop the upper 8-bits?

Thanks,

Jeff

over 9 years ago

0 Sai Reddy over 9 years ago

TI__Mastermind 22640 points

Hello Jeff,

Both the NBRFIFO and uDMA read data sizes of 8, 16 or 32 bits. So to read 24-bit data, you will have to do this manually (that is using the CPU), either while copying from the NBRFIFO to a memory buffer or reading from a memory buffer into a variable.

Thanks,
Sai

EDIT: Modified a previous typo as pointed out by Chris.

0 Jeff McDevitt over 9 years ago in reply to Sai Reddy

Expert 1775 points

Sai,

Did you mean to say "Both the NBRFIFO and uDMA read data sizes of 8, 16 or 32 bits" ?

Thanks,

Jeff

0 Sai Reddy over 9 years ago in reply to Jeff McDevitt

TI__Mastermind 22640 points

Hello Jeff,

Yes it is 8, 16 or 32 bits. I will edit my original post. Thanks for pointing it out.

Sai

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Looking for suggestion on best way to use 24-bit data received via 32-bit EPI FIFO and uDMA controller