about sbc6713 + two A4D4 synchronize question (it is ugent)

[bmrYajun]

Hi supporter,

A customer want to use SBC6713e Plus 4 A/D 100KHz channels and 6 D/A 100KHz channels. I give the customer two solutions.

1. SBC6713e + servo16

the Highest frequency of Servo16 is 100KHz, customer want to use 100KHz working frequency.

Question: Could Servo16 work stable, continuously and long on 100KHz frequency ?

2. SBC6713e + two A4D4

Customer want to Simultaneously use six D/A

Question: Could we let two A4D4 Synchronously work in sbc6713e ? if we can, How do we do ?

regards
Jiang Qiao
BMR

[jhenderson]

Unfortunately, it is not possible to guarantee that the SBC6713 can perform an unspecified series of operations at 100 kHz. Ultimately, the only sure-fire approach is to benchmark the algorithm to be executed on the SBC and verify that it meets your real-time requirements.

The common motif of using an ISR to service A/D and D/A devices on a sample-by-sample basis is almost certainly problematic. The ISR overhead combined with Omnibus transfer inefficiencies and the high load on the CPU intrinsic to this approach means that few real-world applications will run at this rate within an ISR without careful and extensive optimization.

That said, the standard AnalogOut and AnalogIn drivers supplied with the SBC6713e will readily support 100 kHz continuous data flow to or from the Servo16 module. The supplied drivers are EDMA-driven and work on relatively large blocks of samples, to mitigate CPU usage. But, these drivers incur much higher latencies and are unsuitable for servo processing.

[bmrYajun]

If customer use SBC6713e with two A4D4.

I think the two A4D4 should work well at 100KHz, customer want to use 4 A/D 100KHz, it is no problem, but the customer want to use 6 D/A 100KHz channels , Could we let two A4D4 modules Synchronously work on sbc6713e ? if we can, How could we do ?

with best regards

Jiang Qiao

BMR

[jhenderson]

The Pismo target DSP libraries for the SBC6713 and M6713 provide two types of drivers for the Omnibus modules.

The EDMA-driven streaming drivers (Innovative::AnalogInStream and Innovative::AnalogOutStream) are very efficient in terms of CPU usage, since they use the DMA controller to perform all data movement. But, these drivers are block-oriented, and impose substantial latencies as a consequence. So they are ill-suited to applications in which latency is important, such as servo-control applications. Another limitation of this driver is that it requires one hardware interrupt per direction of data flow. The SBC6713e and M6713e each support only four external HW interrupts; Two are required for bus communications, leaving only two free for analog I/O. Therefore, it is not possible to support two modules operating bidirectionally, simultaneously since that would require four additional HW interrupts.

The Servo driver (Innovative::ServoBase) are very low-latency (as low as one sample). However, the CPU is used for all data movement and data processing occurs within an ISR, so this driver is much more CPU-intensive and it is ill-suited to data acquisition applications. This driver can be used to service analog I/O on up to two modules using a single interrupt from a single module. However, it is not possible to predict whether a specific number of analog I/O channels can be serviced using this driver, without benchmarking the specific algorithm being use.