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I have some questions on the process that changes the frequence by the radio controller.
For example:
int WarpRadio_v1_SetCenterFreq2GHz(char freqset, unsigned int radios) which is used to change the board radio to one of the 2.4 Ghz band.
The parm freqset is used as dedicating the band, and the radios is to indciate the index of radio board.
But within this procedure, i found there are at least 3 different registers and several differnt hex value are used for this proces:
Here are 3 specific register:
slave_reg8 - set the transimtting value
slave_reg7 - the value used for radio select
slave_reg5 - set the go_bsy to high to start the transmitting
Here are differnt variables to be transmitted:
reg3, reg4 -- Seems they are transmitted to slave_reg8 regardless of the radio board, i am not about their usage
reg5 -- is set, for example REG_RAD2_BAND_SELECT & mask2g, and then tranmitted to slave_reg8 while radio selection info is sent to slave_reg7 the same time.
So for slave_reg8, there are at least 3 different values are received during this procedure, to change the radio board frequence domain.
I don't know the background for changing the freqence band, and guess if there is a protocol between the radio controller and the tranceiver controller MAX2829. Can you give some clues?
Another question is on the time cost by such an frequence changing operation. I see that, within the trasmit(), the while() is used until the transmission is completed indiating by the slave_reg5. Is this time depending on the MAX2829 device or anything else? I just want to find a means to quantitize the time cost of the freq band swithcing.
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First, please read the relevant sections of the MAX2829 datasheet. Fig. 2, for example, shows the timing of transactions over the SPI interface. The SPI clock output from the radio_controller runs at 20MHz (half the bus clock). With these, you can figure out the theoretical minimum time required to perform 3 SPI writes to change the center frequency. Tables 11-13 list the register values which must be written to select various center frequencies, and the meaning of each bit in the three registers. We used the datasheet to design the radio_controller HDL/C code; the "magic numbers" in WarpRadio_v1_SetCenterFreq2GHz() are all adapted from the MAX2829 datasheet.
To measure the actual frequency change time, I'd suggest using the XTime library to record timestamps at various places in your code, then print these via the the UART afterwards.
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Thanks very much for this detail explaination.
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But I am thinking the XTimer can only be used the measure the time cost on configuring the registers on MAX2829. How can I measure the time for the PLL settling time of changing band on MAX2829. I don't think the slv_reg5 of the radio controller returns depending only when the MAX2829 complete the PLL locking.
Last edited by riveridea (2011-Mar-02 14:38:25)
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I read the datasheet of MAX2829. As my expection: the time on changing the frequence could be two parts:
1. programming the 3 configure registers, each has 18 bits, by SPI port, with 20Mhz
2. PLL locking time, less than 300 us.
In whole, I guess the less than 350us is needed.
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The PLL settling time is measured in microseconds (around 25 usec for a change in the 2.4GHz band; see the bottom-center plot on pg. 17 of the MAX2829 datasheet). I think the only way to measure this yourself would be to probe the radio PLL signals with a high-speed oscilloscope. The radio doesn't provide any register/digital signal to indicate a settled PLL.
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Yes, I see that the 300 us is for the Automatic Sub-band selection. For manual sub-band selection, the settling time is less than 50us, based on Page 30 of datasheet.
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