Ask HN: Hardware business; preventing a competitor from using your driver

I want to start a company selling a piece of hardware I designed. The hardware needs a driver, and I'd like to give people who buy my thing the source code to the driver to let them modify stuff if they want to. The problem is that I'd be a small business, and as I see it, if I open source the driver to my product there's nothing preventing a larger electronics manufacturing company from building and selling something that uses the driver I wrote. So, to protect myself from that contingency, (obviously) I'd include something preventing the sale of hardware that uses that driver in the license to the code. So, I've got two questions:

1. Legalese; anybody law-knowledgeable here who can say how much protection provisions in the license to the code of the driver would offer?

2. Partial-drm solution: To reiterate, I'd really like to give customers the code, but I don't want to inadvertently help a competitor undercut me, anybody heard of a partially-proprietary driver created by a hardware company to solve the problem I'm describing?

Obviously, I don't mean to claim ownership to ideas, only their implementation; but if my thing gets popular I'd prefer it if the company that eventually undercuts me has to through the expense of designing their own stuff.