Self-nesting Interrupt / Jump(CI) Problem

Question

hello, 
 i'm using the ad21489 ez-kit as a SPI receiver/transmitter from/to external converters. 21489 is master (init conversions with PCG). 
 i've chosen a high sample rate of 192 kHz because very low latency is important. It's NOT possible for me to run a slower samplerate!! 
 now, due to the fact that the computations in the ISR needs more time than there is between 2 spi-interrupts, downsampling is required. occuring Interrupts during the ISR should be handled after the ISR, which means they should be self-nesting (like in programming reference, page 4.36) 
 to do so, i want to use the 'jump ISR (CI)' istruction. but this doesn't work. when i run the program it does not jump in the isr. on the second run it immediately stops and i get the error: "Target halted due to software breakpoint but no breakpoint found at address: 0x......". i've searched a lot but can't figure out what is happening. 
 i've attached the code. hope u can help me with this. 
 thx a lot in advance, 
 Tschem

EZAutoReply · Accepted Answer

Hi, 
 Yes, you may have to do a read/dummy read to RXSPI buffer to clear the SPI interrrupt. 
 Thanks, 
 Mitesh)

EZAutoReply · Answer

Hi Tschem, 
 I took a look at the code. But not sure if it can replicate the problem you mentioned directly without having the external converter connected. Could you please confirm? 
 I had few more additional questions: 
 1) I am curious to know if everything else other than the interrupt self nesting is working properly? I mean suppose if you remove the processing part and just loop back the data without down sampling it and thus without making use of the self nesting approach, does that work fine? 
 2) I see that you use a mix of assembly and C code. I hope you are already taking care of recommendations mentioned in the compiler manual regarding using mixed C and assembly codes. For example, compiler may have have some registers which might need to be saved and re-stored in an C callable assembly routine etc. 
 Thanks, 
 Mitesh

EZAutoReply · Answer

Hi Tschem, 
 Thanks for further details. I ran your code again on ADSP-21489 EZ-Kit. I tried to change the WAIT to more than 80 (100), but I couldn't see the error you mentioned in the first post. As I mentioned in my previous e-mail, could you please mention if this error should occur independent of whether the external converters are connected to the EZ-Kit or not? This will help me to understand whether or not it is possible for me to see the same failure here which you are seeing at your end. 
 I also wrote a simple code to demonstrate the functionality of the jump(ci) and rts(lr) instructions for self nesting of interrupts. The code does following: 
 1) Configures the core timer to generate periodic interrupts after every 1000 CCLK cycles. 
 2) Configures the IOP timer 0 to generate a single interrupt after 4500 CCLK cycles to ensure that total four core timer interrupt occur after which both the core and IOP timers are disabled in the IOP timer ISR. 
 3) Has a hardware loop of 1000 CCLK cycles inside the core timer ISR to make sure the the time taken for the ISR to execute exceeds the core timer period of 1000 CCLK cycles. 
 4) To count the number of core timer interrupts recognized and serviced, Inside the core timer ISR, a variable "count" is incremented each time the interrupt occurs. 
 I could see that without using the "self nesting" concept, the final count value is only "2". While, when the self nesting is used, the final count value is "4" which means that all the four timer interrupts were latched and serviced successfully. 
 "The line "#define USE_SELF_NESTING" can be commented/highlighted to switch between the normal ISR and self nested ISR." 
 Please find the simple code attached. Please use this as reference and try to modify your code accordingly and let me know if you still see the same issue. 
 Hope this helps. 
 Thanks, 
 Mitesh