Hi,My goal is to evaluate how fast I can toggle an I/O on the XMC1100.For this, I bought the cute XMC 2Go kit and installed DAVE4.Starting point was t...
Show More
Hi,
My goal is to evaluate how fast I can toggle an I/O on the XMC1100.
For this, I bought the cute XMC 2Go kit and installed DAVE4.
Starting point was the XMC_2Go_Initial_Start_v1.3 example.
I can change the frequency of the blinking led. Toolchain works. Fine.
Then I added the line
P0_5_toggle();
In a while(1) loop.
Toggling works and time from rise to fall is about 3us.
Really slow.
According the comments in the example, the CPU clock is running on 8 Mhz.
Not sure how this works, but I need the 32 Mhz.
Changed the configuration to :
SCU_CLK->CLKCR = 0x0FFC0100UL;
This resulted in toggle time of about 1.2 us.
After this, I replaced the function call to P0_5_toggle() with it's contents:
PORT0->OMR = 0x00200020UL;
This resulted in an improvement to about 530ns.
Oops! The tooling neglects the inline directive of the P0_5_toggle() function. No idea why.
Next step is to execute the toggle code from RAM.
Therefore, I moved the toggling code to a separate function in a separate file (header + c file).
In the function declaration in the header file, I added the famous __attribute__((section(".ram_code")))
However, the tooling also neglects this directive and the code is still executed from flash.
Anybody knows a solution?
It seems that it is a tooling issue.
I tried to understand the linker script, but I did not see strange things.
Thanks,
Lodewijk
--
An investigation of the 530 ns:
The P0_5_toggle() generates 3 assembly instructions (2 loads and 1 store):
LDR: 2 cycles
LDR: 2 cycles
STR: 2 cycles
+ a B(ranch) for the while loop, good for 3 cycles
So, this is 9 cycles. If we assume 2 wait cycles for reading from flash, we have 8 additional cycles.
In total 17 cycles. 17 cycles * 31ns = 527ns.
Show Less
