![\"\"](\"http:\/\/course.ece.cmu.edu\/~ece500\/projects\/s20-teame0\/wp-content\/uploads\/sites\/92\/2020\/02\/PDM_deadbug_tester_closeup-1024x768.jpg\")
<\/p>\nThis week I mainly worked on getting the gigabit ethernet interface working on a development board, and, put together a board for testing the PDM microphones.<\/p>\n
After getting the FPGA toolchain set up last week, I spent most of this week putting together a basic RGMII interface.\u00a0 A significant amount of the time spent was on the IO.\u00a0 Since RGMII is a relatively fast DDR interface, in order to meet timing, I had to use ODDR2 blocks for all the pins.\u00a0 I had never used these before, and had some initial difficulty getting them to work as expected.\u00a0 Additionally, some of the IO that I was using to verify operation were buffered with 74HC245 bus transceivers, which cannot operate at the 125MHz required for RGMII.\u00a0 Once I realized that they were to blame for some of the unusual behavior, I removed them from the board and bypassed their footprints with wires.\u00a0 At this point, the board is able to send a hardcoded UDP packet over the RGMII interface, however, the PHY does not transmit it.\u00a0 I am not sure whether this is because some additional configuration is required for the PHY, the RGMII is not being generated correctly or something else, and, cannot find a datasheet for the PHY.\u00a0 I’ve emailed Broadcom, but haven’t received a reply.\u00a0 Last week I got a sample of a PHY from Analog Devices, which does have a datasheet available online.\u00a0 If I’m unable to get the broadcom PHY working, I will probably either use the AD PHY, or purchase a breakout board for a different chip (several are available online for ~$40).<\/p>\n
I also built a basic breakout board for one of the PDM microphones, and wrote a basic interface using a Teensy 4.0, that sends the raw PDM data over USB.\u00a0 I did not have time to do any analysis on this data, however.<\/p>\n
<\/p>\n
(close up of the microphone)<\/p>\n
![\"\"](\"http:\/\/course.ece.cmu.edu\/~ece500\/projects\/s20-teame0\/wp-content\/uploads\/sites\/92\/2020\/02\/PDM_deadbug_tester-225x300.jpg\")
<\/p>\n
(microphone test board.\u00a0 Dip switches for switching between multiple microphones)<\/p>\n
No significant changes to the plan have occurred, and we are still on track.\u00a0 Our main risk of falling off-track will be that I will have to get at least a basic ethernet interface working, or else pivot to a different interface, within the next week.<\/p>\n
This coming week, I plan to mainly work on the ethernet interface.\u00a0 I’ll be handing off the PDM microphone test board to Ryan and Sarah, going forward, for audio properties and testing data processing.<\/p>\n","protected":false},"excerpt":{"rendered":"
This week I mainly worked on getting the gigabit ethernet interface working on a development board, and, put together a board for testing the PDM microphones. After getting the FPGA toolchain set up last week, I spent most of this week putting together a basic RGMII interface.\u00a0 A significant amount of the time spent was … <\/p>\n