Stack Depth requirements for CP/M 2.2 CBIOS

Hello, I have rewritten my old systems CP/M 2.2 CBIOS to add an IDE Drive. I've run into a problem that has me stumped. Everything works as long as I don't try and copy or assemble a large Assembly file (>80KB). I will be going along fine and then out of nowhere I will see CP/M request access to Drive "T". My debug info says SELDSK is requesting Drive 0FF00h. I have added debug code to all the CBIOS routines so that they report what they are doing to the console (slow but nice). I've gone through my code many times and tested each routine via an embedded debug monitor. I believe I have added every CP/M 2.2 patch (1-6 and 9)that is specific to the CBIOS including those dealing with Blocking/Deblocking. In the back of my mind I kept wondering if I was exceeding CP/M's Stack Depth. I can find no information on the web or in my doc's that specifies what the maximum Stack usage is for a CBIOS. Do any of you have any thoughts on my Stack Question? Are there other issues with Blocking/Deblocking that become visible with large Disk Drives, and that are not covered in any of the published DRI patches? Thanks for your assistance. Robo