Minimum clock speed for SWD?

We're trying to bit-bang SWD to program an nRF52832, and we're running into some problems getting the nRF52 to respond. One theory is we're not generating a high enough clock speed. Right now we're using a 10khz clock.

What's the minimum clock speed for SWD? Where can I find electrical specifications in general for SWD? I can't find them in the ARM Debug Interface Architecture Specification