A little progress on the M4 Board, I managed to get the IPC (inter processor comms) system between the Cortex-M4 and the ESP8266 going.
It uses HSPI interface + GPIO0 on the ESP and SPI1 interface + a gpio on the M4.
SPI comms from ESP to Cortex-M4
Cortex-M4 acts as spi-slave, it will listen to the any incoming HSPI command from the ESP, via SPI_RXNE interrupt (on SPI1 irq handler, max. 42 MHz).
The irq handler is done with some very optimized assembler code and simply buffers whatever is send from the ESP, whenever there is something in the rx buffer. It also deals with sending any data if there is something in the transmit buffer to send.
HSPI CS will trigger an external interrupt on both edges on the M4.
When HSPI CS goes low, it will clear the index of the spi1 rx buffer.
When HSPI CS goes high, it will process the command/data received in the spi1 buffer.
Cortex-M4 to ESP
GPIO0 is set as input on the ESP and the M4 will pull this low whenever it wants to send command/data to the ESP. Prior to that command and data is written to the transmit buffer of the SPI IRQ handler.
This triggers an interrupt on the ESP, which will then start clocking dummy data out on the SPI to read/process the responses (full duplex).
This wont come in any faster than the ESP is driving the clock. The HSPI clock is set to 40 MHz.
This system works pretty well now. It’s not as fast as I’d like. Currently transfer is about 500 KB/s, while I can download to the ESP with about 900KB/s under optimal conditions.
So the SPI IPC is a bottleneck, however there is still room for improvement.
As the clock speed is really fine on the SPI, the problem is the delay between each byte write from the ESP which is done via CPU writes.
Ideally I could use DMA, but there seems to be no info on this anywhere in regards to the ESP.
Another option is to use 16 bit read/writes instead of 8 bits and probably almost double the speed.
Or I could use the entire 64 byte buffer of the ESP HSPI interface and clock them out nicely without delays 64 bytes at a time.
On the hardware side, I have re-designed the board and ordered new pcb’s. I screwed up the footprint of the GTL2000 chip and there simply was no way about. Obviously other improvements & fixes were added.
After ages of waiting for components to arrive from China (and some didn’t, so I had to reorder).
I was finally ready to assemble the M4 board. After applying the solder mask and doing pick and place, I found the GL2000 bi-directional level converter was the wrong package :/ – Oh well added the other components as there is enough work to do without it for now. Also a couple of other screwups, ie. swapped miso and mosi on the flash, used wrong SCK pin on ESP-12E (notice it is PIN 12 that’s spi-clock). So eventually I will have to re-do the PCB.
Update: It’s not entirely true, it is because there is two (known) different ESP-12E modules in existence, see here http://www.esp8266.com/viewtopic.php?f=5&t=3163 My initial layout wasn’t wrong, I just got a 12E module with a different pin layout :/
For now, the MCU, SD and SPI flash is working, I can access the ESP8266 wifi chip and read/write the spi flash from the Cortex M4 (keep the ESP in reset state and do spi access) and obviously send serial commands.
However the plan is to make an IPC interface via SPI between the Cortex M4 and the ESP-8266 to get proper performance.
I will update on this as I get along.
A side project to log industrial robots via their PLC (24V) interface.
The PCB consists of:
- ST32F407VGT (Cortex M4) as the MCU.
- SD card for storing detailed logs.
- DP83848 ethernet PHY hooked up to the M4 RMII interface, connecting it to the LAN, so logs can be downloaded, statistics viewed, live view, settings and more.
Using netbios names and DHCP by default, so easily accessible without pre-setting.
- Optocouplers to completely seperate the PLC signals from the board.
- Battery backup for SRAM and RTC, even poweroff’s are logged.
- Status leds for Power On, SD card OK, Ethernet OK, MCU running (flashing).
- Firmware upgradable from LAN/Internet or microSD.
The PCB was designed to fit a compact DIN rail case and using screw terminals for power and PLC signals.
For once it was a really smooth experince, only screwed up the battery polarity, which was easily fixed by using another holder.
After a long wait, the last components for the USB 3.0 to FPGA board arrived. Board is now reflown.
Both ends work, Spartan 6 FPGA detected via JTAG and FT601Q detected via USB3.0.
Being occupied with a few other projects at the moment, it probably will take a bit before I have time to write the appropriete VDHL and Windows D3XX code to fully test it. Hopefully in a few weeks I’ll be able to get some realtime fast data acquisition going with it.
Having a few spare ST32F407 chips collecting dust, I decided to make a neat little board for it. Featuring USB, JTAG, microSD, 32Mbit spiflash, WiFi, 18 GPIOS with 3.3V / 5V bi-directional level translation for a special purpose 🙂
Cortex-M4 is a great ARM MCU running at 168MHz, 192KB ram and 1MB flashrom. The one in use is a ST32F407VGT in a TQFP100 package, all GPIO’s are routed, no components backside. Board size 76×66 mm.
Still waiting for my USB3.0 FPGA boards to arrive.
Done the pcb,
just need to fix up the silkscreen and re-check everything before sending it to a fab house. Now sent to pcb manufacturer.
The board features the FT601Q Super speed (QFN76, 9x9mm!) connected to an Xilinx Spartan 6SLX9TQG144 FPGA.
All routed in 2 layers – yeah I know it’s not pretty, I am just happy if it works…
Just made an Eagle library for the USB3.0 fifo chip FT601Q, that I am planning to use for a board. More info about the SuperSpeed USB3.0 chip over at FTDI chips.
Attached the Eagle lbr here in case anyone wants to save some time.
Notice it’s untested as of now.