nRF52832: UART buffers, PHY interface questions

[joedamato]

Hi,

Context

The chip will be a slave of a powerful CPU which is responsible for many coordinating tasks. The chip will connect the CPU via UART. I am interested in BLE.

It is important to minimise the interrupt rate and grab multiple bytes at once to improve efficiency.

Question

1. So, how large are the UART buffers and can we programmatically increase them?

2. Wouldn't a PHY interface connected to the CPU improve performance vs UART? (Not sure you have such product though)

Thanks

[RK]

1. With EasyDMA list mode the buffers are pretty much as big as you want them to be, subject to available RAM.

2. I don't understand this question at all. You use PHYs when you interface MACs to different physical transport mediums, here you are connecting two chips with traces.

I wouldn't use UART for this myself unless I had to, I'd use SPI, which you can run up to 4MHz. Also since the master controls the clock, it can clock in data whenever it wants, you just have to keep the buffers on the nRF full.

[joedamato]

My goal was to avoid those slow protocols by directly connecting the chip MAC with the CPU MAC interface (Cortex A53 support that). That would make this solution native BLE and potentially faster by reading bounds directly and accessing buffers in a very fast fashion.

[RK]

no you can't connect anything direct to the CPU, the buses are not exposed, there is no peripheral which is external memory mapped. And I'm not sure I'd call 4MHz SPI a slow protocol, that's 4x the underlying bit rate of BLE, which has an effective bit rate lower than that anyway.

Data rate's not your problem, if you have a problem at all it's available RAM for buffering the data you want to stream on and off. And if that is a real issue for you, you're using the wrong chip.

[joedamato]

RK, thanks for your inputs. You are right I will use SPI. One side question though: are there some wifi chips that expose their buses? Or is it just a Ethernet thing?

[RK]

Haven't come across any - the closest in my mind is the built-in PCIe on the Intel chips which is blisteringly fast and is so native it's almost part of the bus. Then there's varying types of external memory, from DRAM, which is on the bus to some of the chips which have a simple parallel peripheral you can use a few pins to interface to . Beyond those and the ability of two processors from the same family to work together, not really.