Hi,
I just compiled gr-fosphor on a PC equipped with a HD 5450 card, and when I try to run osmocom_fft -F I gut the following error:
[+] Selected device: Cedar Build log for 'display.cl': "/tmp/OCL2287T8.cl", line 67: error: work group size exceeds the maximum default value for the selected device __attribute__((reqd_work_group_size(16, 16, 1))) ^
1 error detected in the compilation of "/tmp/OCL2287T8.cl". Frontend phase failed compilation.
Yes, that card only suppot 128 as a maximum work group size and fosphor is written to use 256. I think this particular generation of card is the only one that's new enough to support OpenCL but old enough to not support WG of 256.
I did however write a patch to support it a while back and just never bothered to clean it up (to select size dynamically depending on your card).
Try the attached patch and see if it works for you.
Cheers,
Sylvain