pseudo random number between X and Y?
in [Embedded]
|
From: Go Rf on 17 Nov 2009 08:06 Hello all I need a function, when called returns a pseudo random number between X and Y. I have many boards that periodically broadcasts their board addresses on an RF link. All boards use the same RF-channel frequency, so data collisions is going to happen. So I need to randomly delay between those broadcasts to be able to avoid collisions with other boards broadcasts. I want to make a pseudo random delay (X ms - Y ms) before sending the package again.
From: Paul Keinanen on 17 Nov 2009 08:22 On Tue, 17 Nov 2009 14:06:07 +0100, "Go Rf" <Rf(a)Rf.org> wrote: >Hello all > > > >I need a function, when called returns a pseudo random number between X and >Y. > > > >I have many boards that periodically broadcasts their board addresses on an >RF link. All boards use the same RF-channel frequency, so data collisions is >going to happen. So I need to randomly delay between those broadcasts to be >able to avoid collisions with other boards broadcasts. > > > >I want to make a pseudo random delay (X ms - Y ms) before sending the >package again. Why not just use some microsecond counter and use some of the lower order bits as delay, if receivers detect a collision situation. Even with mains powered systems, a typical microprocessor crystal will soon drift so much that collisions do not occur frequently after a mains failure. Paul
From: Paul Keinanen on 17 Nov 2009 08:39 On Tue, 17 Nov 2009 15:22:28 +0200, Paul Keinanen <keinanen(a)sci.fi> wrote: >On Tue, 17 Nov 2009 14:06:07 +0100, "Go Rf" <Rf(a)Rf.org> wrote: > >>Hello all >> >> >> >>I need a function, when called returns a pseudo random number between X and >>Y. >> >> >> >>I have many boards that periodically broadcasts their board addresses on an >>RF link. All boards use the same RF-channel frequency, so data collisions is >>going to happen. So I need to randomly delay between those broadcasts to be >>able to avoid collisions with other boards broadcasts. >> >> >> >>I want to make a pseudo random delay (X ms - Y ms) before sending the >>package again. > >Why not just use some microsecond counter and use some of the lower >order bits as delay, if receivers detect a collision situation. > >Even with mains powered systems, a typical microprocessor crystal will >soon drift so much that collisions do not occur frequently after a >mains failure. I would like to add that the microprocessor system crystal drift is so bad that in one system with identical processor cards distributed over a large area, the drift was so bad after a reset signal on the common serial line (break) the system became useless after a few seconds due to the crystal drift at various boards. We had to use the 50 Hz mains (with very bad short time accuracy) as our common timing reference. Paul
From: Wil Taphoorn on 17 Nov 2009 08:51 Go Rf wrote: > I have many boards that periodically broadcasts their board addresses on an > RF link. All boards use the same RF-channel frequency, so data collisions is > going to happen. So I need to randomly delay between those broadcasts to be > able to avoid collisions with other boards broadcasts. > > I want to make a pseudo random delay (X ms - Y ms) before sending the > package again. The boards use different addresses I assume. Should a delay calculated from (part of) the board's address not suffice? -- Wil
From: Go Rf on 17 Nov 2009 09:08 "Wil Taphoorn" <wil(a)nogo.wtms.nl> wrote in message news:WTMSB29E82BE(a)wtms.nl... > The boards use different addresses I assume. Should a delay calculated > from (part of) the board's address not suffice? The boards use a 32-bit address that is unique. So I should be able to use it. If I for example take 8-bits from theboard address to specify a delay. And the next time I take the next 8 bits. For example delay = bit(7 to 0) of address delay = bit(8 to 1) of address delay = bit(9 to 2) of address .... delay = bit(31 to 24) of address and then start again at: delay = bit(7 to 0) of address But some combinations of addresses works better than others. And it gets bad if i enumerate all boards starting at address 1 and the 2, 3, 4, 5 etc.
|
Next
|
Last
Pages: 1 2 3 4 Prev: OpenOCD+GDB (stepi. Unable to single step) Next: Compact Flash IDE PIO Write Size Issues |