How to verify a detached signature in an embedded device

[Voser Peter]

Hello, 
I want to verify a detached signature in a boot loader. 
The boot loader is built using the GNU toolchain for my 
processor, but there is no OS available (no file system, 
no shell, no stdin/stdout, ...). 

I have the signature as well as the public key and the 
corresponding text as character arrays in the RAM. 
Also, I know how long the corresponding arrays are. 
Is there a possibility to verify them? Has anyone 
already written this code? Or: can anyone give me a 
tip how to modify the gpgme lib? I looked at the source 
code of the gpgme lib, but it assumes to have an OS. 

The function I dream of looks as follows: 

int isSignatureGood(char *signature,
                    int signatureSize,
                    char *publicKey
                    int publicKeySize,
                    char *text
                    char textSize);

Thank you, 
Peter Voser