AVR UART regarding RTS/CTS

RE: AVR UART regarding RTS/CTS

Ole Bauck — Fri, 01 Apr 2016 09:29:55 GMT

Ok, but is the nRF receiving all the bytes? Try printing out the bytes to a terminal as you receive them using uart or RTT.

RE: AVR UART regarding RTS/CTS

erltot — Fri, 01 Apr 2016 08:38:56 GMT

Correct. I am using another mcu to "spy" on the uart between avr and nrf and it shows the messages the way I expect

RE: AVR UART regarding RTS/CTS

Ole Bauck — Fri, 01 Apr 2016 07:56:32 GMT

Looks more like you are missing some parts instead of wrong order. This may be due to no hardware flow control (you didn't use that right?). Could you check that everything is received on the uart?

RE: AVR UART regarding RTS/CTS

erltot — Thu, 31 Mar 2016 18:22:14 GMT

It's almost working. Instead of crashing it sends some parts of the string in the wrong order after a while; Sending "A B C D E F G H I J K L M N O P Q R S T U V W X Y Z \r\n" every 200 ms:

...    
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
A B C D E F G H I J U V W X Y Z 
K L M N O P Q R S T A B C N O P Q R S T U V W J K L M X Y Z

RE: AVR UART regarding RTS/CTS

Ole Bauck — Thu, 31 Mar 2016 16:06:56 GMT

Something like this: http://pastebin.com/ETYguyPd

RE: AVR UART regarding RTS/CTS

Ole Bauck — Thu, 31 Mar 2016 15:54:48 GMT

You will get the best throughput with S130 v2 at the master and either s110 or s130 v2 at the peripheral. S120 will not give you better throughput.

20 byte packet is 20 bytes, a 20 character string will be 21 bytes due to the null terminator.

Error code 7 means NRF_ERROR_INVALID_PARAM. Which is probably because length is greater than BLE_NUS_MAX_DATA_LEN (see in ble_nus_string_send function).

Your code will most likely wait for very long time in while(true) statement in uart_send_flowcontrol(). In this case it is better to have another approach: If BLE_ERROR_NO_TX_PACKET is received store the packet in a buffer (f.ex. use app_fifo). When BLE_EVT_TX_COMPLETE is received check if there are any packets in the buffer and send them out if so.

RE: AVR UART regarding RTS/CTS

erltot — Tue, 29 Mar 2016 14:01:08 GMT

I am using S130 from SDK10 on both peripheral and central, are you saying I will have a better throughput if I switch to S110 and S120?

And just to clarify; is one 20 byte packet as you write to be considdered a 20 byte string, as I see the dongle split it in the terminal when sending a longer string via the BLE APP UART example?

I tried to add the flow control fix, I probably made a mistake somewhere, I could recieve the string I tried to send before it crashed. I get error code 7 from ble_nus_string_send. I could not figure out what that mean.

Code: http://pastebin.com/nXEKJXcB

I added the function previous known as heart_rate_meas_send to line 101 "uart_send_flowcontrol" and copied the code from the uart event function (this is probably where mistakes were made) and added the function call in on_ble_evt at line 347

RE: AVR UART regarding RTS/CTS

Ole Bauck — Thu, 17 Mar 2016 15:06:24 GMT

I checked the central code and it uses connection interval min 20ms and max 75ms. It will choose the min value if it can (depends on number of peripherals it is connected to).

RE: AVR UART regarding RTS/CTS

Ole Bauck — Thu, 17 Mar 2016 15:02:02 GMT

When I said "flow control" I meant the "wait for TX_COMPLETE event before sending new packets" (that's why I put it in apostrophes ;)).

With S130 as central you can receive 3 packets per connection event. Maximum throughput with 7.5ms is 63.4kbps assuming the peripheral side can send the same amount of packets, see here. Which SoftDevice are you using on the peripheral side? If you are using S130 you can only send two packets per connection event. What is your connection interval? You will be able to send the amount of packets if you use low enough connection interval:

bitrate = nr of packets per connection interval * 20bytes per packet * 8bit per byte / connection interval

RE: AVR UART regarding RTS/CTS

erltot — Thu, 17 Mar 2016 09:46:03 GMT

Are you refering to flow control on the BLE link(nRF51 to nRF51) or the UART link (nRF51 to AVR)?

I am using another nRF51 dongle as central, perhaps I can adjust some settings on this to achieve higher throughput? My central is running an edited version of Marco Russis' BLE multilink NUS Central: github.com/.../nrf51_multi_nus_central

My 270 bytes per second from the 54 character string every 200 millis from the peripheral to central seems a long way from the 5 300 bps - 128 000 bps mentioned in the thread you linked to, or am I mission something fundamental about this? How small is a small package?

RE: AVR UART regarding RTS/CTS

Ole Bauck — Thu, 17 Mar 2016 09:32:23 GMT

The example referred to in the post I linked to is from ble_app_hrs example. But the function ble_hrs_heart_rate_measurement_send(..) will call sd_ble_gatts_hvx(..) just as ble_nus_string_send(..) is doing.

The UART example will only divide the input over uart in packets of 20 bytes and send it over BLE. If you implement the "flow control" in the link, the example will max the throughput as long as UART bitrate is larger than BLE bitrate.

If your connection interval is over 200ms and the number of packets you can send per connection event is low (this is for most part limited by the central, take a look at this post), you may not be able to get that throughput.

RE: AVR UART regarding RTS/CTS

erltot — Wed, 16 Mar 2016 19:18:08 GMT

I could not completely relate the example you linked to, to the BLE_UART example, could you give an example for this as well?

I thought the UART example had maximum throughput allready, but it should be alot more than what I am trying to send, which would be around 265 bps (a string of 54 characters every 200 millis)

RE: AVR UART regarding RTS/CTS

Ole Bauck — Tue, 15 Mar 2016 09:41:52 GMT

The issue is not with the UART, but with the BLE link. You are sending too many packets and the ble_nus_string_send(..) function is returning BLE_ERROR_NO_TX_PACKETS (error code 0x3004, previously called BLE_ERROR_NO_TX_BUFFERS). The error code originally comes from the sd_ble_gatts_hvx(..) function which is called inside ble_nus_string_send(..).

See for example this post on how to handle this error code and send large amount of data. You should also make sure that the UART buffer (defined in APP_UART_FIFO_INIT) is large enough to buffer the data that are to be sent over BLE.