How different is SHA-512/224 when compared to SHA-512? I understood from the NIST SHS specifications (FIPS 140-4) that the difference between SHA-512 and SHA-512/224 the two differences are the initial hash value and the final result truncation
I changed the initial hash value of SHA-512 to that one of SHA-512/224 as specified in the SHS specifications and then built the CAVS tests. Then I started testing against the copied CAVP test vector.
Lets consider the first case:
Len = 0
Msg = 00
MD = d14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f

But the result I am obtaining for the above input is:
SHA512/224 digest
     6ed0dd02806fa89e25de060c19d3ac86cabb87d6a0ddd05c333b84f4

Lets consider the second case:
Len = 8
Msg = 84
MD = 3cd36921df5d6963e73739cf4d20211e2d8877c19cff087ade9d0e3a

But the result I am obtaining for the above input is:
SHA512/224 digest
     8f8fdcb3f617a2d809b3132860b02fee00bdd927d541d42073dd12e7

What am I doing wrong?
As stated by FIPS 186-4 (6.6) The only two differences between SHA-512 and SHA-512/224 are the eight 64-bit words used for initialization, given by FIPS 186-4 (5.3.6.1); and result truncation to the first 224 bits of the 512-bit result: $H_0^{(N)}$, $H_1^{(N)}$, $H_2^{(N)}$ each 64-bit, and the high-order 32 bits of $H_3^{(N)}$.

I suggest to start by checking the SHA-512 implementation pass test vectors; then implement the truncation, and test; then change the initialization value, and test.

[epilogue: that was the test vectors, see this]