Hi Karol,
Here is what is happening in the Serial Send subsystem:
- The goal is to send data to the host at a fast rate and insert delimiters around a large sequence so the host reads a large chunk of data at a slow rate instead of small pieces of data at a fast rate.
- On the host side, it's impossible for Simulink to read 2 Uint16 data points at 200kHz, but Simulink can easily read 12,000 x 2 Uint16 data points every 60ms (~17Hz). The turnaround time makes it easy for Simulink in the second case, though it's the same amount of data.
- On the target model (DCDC_Buck.slx), the purpose of the Serial_Send subsystem is to send data at a fast rate (2 Uint16 data points at 200kHz) and insert delimiters every 12,000 hits.
- To do so, I use a counter that counts from 0 to 11,999. When the counter equals 0, I insert the end of the previous sequence ('EE') and the beginning of the next sequence ('SS'). 'EE' (0x4545 in ASCII) and 'SS' (0x5353 in ASCII) are arbitrary delimiters. Just make sure they match what you use on the host, you can use whatever you want, I picked S for Start and E for End, and I used 2 characters for each to match the Uint16 format of the delimiters.
- When the counter equals 0 I need to send 4 Uint16 data points. The 2 delimiters + the 2 signal data points.
- When the counter is different than 0, I need to send only the 2 signal data points.
- The counter feeds an "if" condition for the 2 above cases. The merge blocks are used to combine the outputs of the 2 conditions into one. The merge block will pick the output of the subsystem that is active at that time step.
- I can only use one Serial send block, and in the start case I need to send 4 Uint16 data points while I need to send 2 in the other cases. To do that I use a "While Iterator Subsystem". It's the equivalent of a "while" loop in C. I will loop 4 times in the Start case to send 4 Uint16 data points and twice in other cases to send signal data.
- The Serial_Send subsystem is scalable to different widths. Pay attention to the baudrate if changing the width of the signal. Serial communication usually sends 10 bits per data byte (1 start bit and 1 stop bit + 8 bits of data). At 200kHz, 2 uint16 data points mean 2x2x10x200000 = 8Mbps needed, neglecting the delimiters. The baudrate on the target is set to 12.5Mbps which should accommodate for 8Mbps. Increasing to 3 uint16 signals should still work as it will push the baudrate to a little more than 12Mbps, but that is very close to the limit. 4 signals will be too many and will not work at it would require 16+Mbps.
I hope it helps,
Antonin
