I welcome you to my review about EK-RA2L1 evaluation board featuring microcontroller from RA2L1 family. In this part I will describe evaluation board itself. I will also describe some of my opinions about board, some pros and cons, some bugs and many other. In this article I will not describe microcontroller itself. Microcontroller is described in dedicated chapter Review of RA2L1 Microcontroller. Except these two review parts there one tutorial showing how to utilize basic bus drivers, DMA and how to setup interrupts. Final score and summary are present at main page of review which is marked by yellow star in following table of contents. Following table of contents contains links to all parts of my review.
- Review of Renesas EK-RA2L1 Development Board
- Review of Renesas RA2L1 Microcontroller
- Using Serial Bus Drivers, DMA and Interrrupts on Renesas RA2L1
Overview of the board
At the beginning I likely to describe what we can find on evaluated board. Whole board looks as follows:
There are 3 interesting chips. First and the biggest chip is main MCU. It is Renesas R7FA2L1 MCU. I will refere this chip as main MCU in this review. Following image highlight main MCU:
But there are second MCU. It is Renesas S124 MCU and this MCU acts as debugger. It is highlighted on following image:
The last chip is LDO voltage regulator which is used to convert input 5V supply to 3.3V voltage which is used for powering both MCU and other components. LDO is highlighted on following image:
Except chips there are 8 interesting connectors. There are Arduino Uno compatible connector:
There are two PMODs which you can use for connecting PMODs which are usually known in FPGA world:
There are MicroBus connector for connecting expansion boards in this form factor:
There are two grove connectors used for connecting I2C sensors:
There are one qwiic connector used for connecting I2C sensors connected using this kind of connectors:
And finally, there are 4 standard 2.54mm connector exposing all the MCU GPIOs:
This is lot of connectors for connecting many sensors and actors available in market.
Another component which is present on board are jumpers. All jumpers are pinheads with 2mm pitch and not a standard 2.54mm. they are smaller which is fine, but they are harder to manipulate, I think. There are 5 jumpers.
First jumper is designed to select boot mode. Main MCU has integrated bootloader and using this jumper you can try this feature on your evaluation board (for example, testing this procedure before going on production). Jumper is 2 pin and by default opened but it is bundled in package. Jumper is connected in a way that one pin is used for holding them and second pin of jumper fly in air (is unconnected). Jumper is highlighted on following image:
Jumper J6 is used to disconnect boot mode selection signal from the connector used for debugging external MCU by onboard J-Link or for debugging onboard MCU by external debugger. When used as standalone board and used with onboard debugger, you do not need to worry about this jumper. Jumper is highlighted on following image:
Other jumpers are related to debugging options. Board support multiple debugging options which would be described later, and these jumpers are used for selecting debugging mode and configuration.
There are 4x2 pin jumpers used for disconnecting SWD (and on some kits possibly connect JTAG wires also) wires from main MCU. Only two pairs of signals are used on this kit. Jumpers are highlighted on following image:
Below the debugger chip there are additional two jumpers. Both are used for configurating debugging mode. There are three possible modes of debugging. Renesas refer them as Debug On-Board, Debug In, Debug Out. Using these two jumpers you can select required mode. Technically jumper J8 is used for connecting RESET pin of MCU to debugger, ground or nowhere and J9 is used for holding debugger MCU (Renesas S124) in reset when external debugging is required. Jumpers are highlighted on following image:
Except already described components there are 3 buttons (2 blue buttons connected to GPIO ports and 1 red button connected to reset) and 3 LEDs - red, green and blue. While they feature all three RGB channels they are separate by space so, you can watch them independently.
Last interesting feature which I want to mention is onboard small value accurate resistor which can be used for connecting current sense amplifier (or oscilloscope doing the same thing). Vendors usually provide just a jumper for connecting amperemeter but because of low consumption and high clock frequency used in modern MCU using amperemeter is less interesting in these days and current sense amplifiers may be a better choice, so this feature is welcome, I think. Probes for connecting external current sense amplifier to onboard shunt resistors are highlighted on following image:
The board is visually horizontally separated using line. The upper part is referred as an “Ecosystem & System Control Access Area” and the bottom part is referred as “MCU Native Pin Access Area”. The upper part is standardized and is very similar between all kits inside RA-EK family. The only difference between boards is that some boards have left-side USB connector connected to evaluated MCU, but RA2L1 MCU’s has no USB peripheral, so there are is no connector. The pin access area differs per kit and mostly differs in the number of exposed pins. Boards evaluating MCUs in 64pin package has less pins exposed here and similarly boards with MCUs with 144 pins have more pins there. RoadTestted board feature 100 pin MCU and all GPIOs are exposed here.
Classification of board
The EK-RA2L1 is one of evaluation boards evaluating Renesas RA family. There are many very similar kits which differ mainly in evaluated MCU and some kits have special features area which enables you to evaluate some advanced features offered by evaluated MCU. Except these EK-RA kits Renesas offers many boards classified as evaluation kits and many breakout boards. Except EK-RA kits I did not find any significant similarities or hierarchy in these boards. Board name refer to evaluated MCU. RoadTested board is named EK-RA2L1 and this means that evaluated MCU comes from RA2L1 family. Similarly, for example EK-RA6M4 evaluates MCU from RA6M4 family, so naming convention is easy.
Board can be powered by USB connector and this is probably most common way of powering board. Other powering option is using expansion connector. Power supply voltage is fed into pretty powerful LDO which converts it to 3.3V. Then 3.3V is used for powering all chips and peripherals. This voltage also power S124 chip used as J-Link OB debugger. Voltage is not adjustable and this I consider as a one of the most significant cons of board because MCU operating range is between 1.6 to 5.5V allowing all common operating voltages 1.8V, 2.5V, 3.3V and 5V and it would be nice to have possibility to evaluate RA2L1 MCU in full range rather than at 3.3V only. Many modern competitors boards support switching between 1.8 or 3.3 but on EK-RA2L1 it is impossible or highly complicated to do this. I personally think that this restriction come from the fact that both chips (main MCU and Debugger MCU) are powered from the same voltage and Debugger MCU needs 3.3V because of USB operation. On competitors boards it is usually resolved by making two voltages, allowing user to select voltage for main MCU, fixing voltage of debugger MCU and including level convertor in design, but there is nothing like this.
To this category can be also classified current sense low-value shunt resistor which can be used for external current sense amplifier (or oscilloscope) and which I have described in previous section.
For debugging purposes there are additional MCU from Renesas. This MCU runs SEGGER J-Link OB (on-board) debugger which is on-board variant of full-featured external J-Link debugger. J-Link is best in class debugger and on-board variant features similar features (SEGGER mentions that it supports exactly the same, but this is not true due to licensing issue as described later). Debugger is very reliable and runs on very high speed without any issues. Debugger is fully supported within Renesas e2 studio and it is supported within many tools provided by SEGGER but note that not all features of all tools are available. Nice example of this is SEGGER J-Flash tools. This tool allow you to read firmware without any issues but it do not allow you to program new firmware to the device because of license issues. You need to buy license from SEGGER if you want to use this tool in combination with J-Link OB. Standalone version of J-link do not come with this restriction, I think.
Interesting debugging feature is RTT (Real-time transfer) which is alternative to debugging UART. Many MCU evaluation boards connect one UART interface of evaluated MCU to the debugger MCU and debugger MCU emulates USB-to-UART bridge. But on this board, there are no UART signals connected in this way. Instead of this there are alternative feature named RTT. RTT works in a way, that firmware stores transmitted text in buffer in MCU memory and debugger periodically reads it using debugging interface (SWD/JTAG). This has some pros and some cons. One of benefit of this is performance and this implies two things. First, UART is pretty slow bus. Commonly used baudrate 115200, 1 stop and 1 stop bit and no parity means throuput of only 11,52 kB per second. Second performance-related reason showing that RTT is better is that transmitting byte over UART is on most MCUs blocking operation which in most implementations prevents MCU running when transmission is in progress. None of these apply for RTT. RTT operation is at MCU side just a memcpy operation and debugger can read data from this buffer at background. Access to the memory by the CPU core and debugger at some time probably slightly affects program execution but this is negligible delay in comparison with UART overhead. The disadvantage of RTT is that it require buffer which costs you a memory. Another disadvantage is that you cannot use your favourite serial terminal, but you are limited to tools that support this protocol which usually are only tools from SEGGER.
After some time spend with development on this platform, I think RTT is good, and I like it. At development time I faced issue being RTT viewer frozen but reconnecting RTT viewer fixed the issue. Development environment support J-Link OB well and debugging is very reliable. I did not face any strange situations with J-Link OB which sometimes happen when working with open-source based tools like OpenOCD.
Pins and connectors
Pinout is pretty fine, but there are some issues which I consider as a bad design. In bottom area of board all GPIOs of MCU are exposed including pins which are connected to some ports on connecters in upper area. This is fine. I utilized these bottom pins for connecting logic analyser to peripherals connected to the upper parts and I liked it very much. Technically this is done well but there two wrong pin labels. I will describe in following section. But there are one another significant issue. The issue is with multiplexing signals between connectors. It is done very extensively on this board. In some cases, it is justifiable. It is for example case of I2C signals. I2C signals are multiplexed between one groove and qwiic and one PMOD, but due to nature of I2C bus this is not the issue. Also note that both PMODs have their own I2C bus and similarly both GROVE connector is connected to non-shared bus so you can connect 2 devices with the same address to them and utilize them at the same time. Biggest multiplexing issue, I consider on SPI bus and especially on Slave Select wire. SPI signals including SS are multiplexed to the one PMOD, Arduino connector and MicroE connector at the same time so you cannot use multiple (even different) SPI devices at the same time connected to these connectors. Sharing bus signals is not a problem but sharing SS signal is. If you want to use multiple SPI devices at the same time in these connectors you must yourself ensure that you do connect some other GPIO to SS pin on your sensor/board. I think selection of pins used for SS on SPI bus was wrong and designers in Renesas can select (even generic without SPI SS support) different GPIOs per connector with SPI exposed next time.
As I have described in previous section there are bugs in pin labels. I found two bugs which can make very hard time when troubleshooting issues caused by them and especially when you do not know about them.
The first bug is that there are two pins labelled as P401 but one of them should be P404. The second wrong label is P211 (in fact P211 does not exists on RA2L1 MCU at all) which should be P214 instead. Both bugs are highlighted on following image:
Note that schematic has correct pins assigned as shown on following image. Bug was probably introduced by engineers in the process of designing PCB by manual silkscreen label placing.
Except these two bugs pin labels are correct and very useful. There are plenty of other labels including very smart description of MCU parameters, board name, MCU name, product code, revision number, Arduino signals are labelled well and so on. I lack some labels describing purpose of test points, but this is minor issue. My last note in this section is that some labels on bottom side of board are placed over vias. Some affected letters look little bit deformed, but this also is not a significant issue and even affected letters are still easy to read.
The board have small rubber stands so it is stable on the desk. If you do not trust small rubber stands protection in conductive desk (or inside device If you want to use this board directly instead of designing own PCB), you can use available holes with stand-offs.
Packaging and default software
Board comes properly packed inside antistatic bag. Board came in paper box with three cells. One of them was empty, one contained board and last one contained USB cable. Board was preprogramed with demonstration firmware which would be used to check that MCU, buttons and debugger are working. Demonstration firmware also utilize SEGGER RTT, so if you have no experience with it, this will be your first “meeting” with this technology.
Comparison with STM32 Nucleo
The EK-RA kits looks like strong competitors to STM32 Nucleo kits. These boards have many common properties. Both EK-RA and STM32 Nucleo kits are available in many variants evaluating different MCUs form their vendors. Both board families have vendor standardized form factor and both board families are designed in way allowing accessing every pin of MCU. But of course, layout of boards is different, used MCU is different and external peripherals are different. While STM32 provides multiple sizes of NUCLEO boards, EK-RA kits sizes differ only in size of special functions area (which is third are separated by visual line on board but this area is not present on RoadTested entry level kit). EK-RA kits have 2 PMOD connectors, 2 grove connectors, qwicc and one click connectors which are not present on NUCELO boards. If you use expansion boards with compatible connectors you may consider it as advantage. Other difference is in used debugger. ST uses their own ST-Link but Renesas use licensed SEGGER J-Link on this kit (which is quite interesting because some other Renesas Kits, like previously RoadTested Renesas RX72N Envision Kit, have their own E2 lite emulator instead of SEGGER J-Link OB). Both approaches have some pros and cons, so I do not consider none of them as significantly better. The benefit of STM32 NUCLEO I consider selectable operating voltage between 1.8V and 3.3V. In opposition as a benefit of RA-EK kits I consider more standardised approach of placing special features (in visually separated area) and easier selection of required features. Renesas provides better documentation making kit selection much easier. ST has some catalogues, but they contain only brief diagrams and then there are extremely detailed description. Nothing between. In opposition, Renesas provides fantastic presentation “An Introduction to Renesas Advanced (RA) MCU Kits” which you can find at main pages of all EK-RA kit. In this presentation you will find described concepts of boards, their hierarchy and main differences between them. This significantly simplify selection and you find ideal board for you in less than minutes. In comparison, searching for ideal NUCLEO board is more challenging because there are plenty of very similar boards and catalogue distinguish them only by form factor, available flash and RAM memory and basically in term of crypto accelerator but if you for example interested in NUCLEO boards with ethernet availability, I never found efficient way how to find them. After RoadTesting time I still cannot make decision which one is better. They are very comparable, and I like both board families.
Documentation is very high quality and I like it. Documentation related to MCU I will not cover here, and I will cover it in Review of Microcontroller chapter. The most important document related to development board is user manual available to download at Renesas website. User manual is well written, easy to read, detailed enough, contains all important information, quick start guides and many more. Except user manual there are available full schematics of board and all manufacturing data. Schematics is easy to read and structured well. I like all provided documentation and over whole RoadTesting time I did not find any missing information or mistake in documentation.
Price and Availability
EK-RA2L1 kit is available for about 80 USD which I consider as expensive when you take in account that this board evaluates one of the most entry level MCU in their families and except MCU does not have any expensive component onboard. Prices grow with complexity of board. For example, EK-RA6M4 which features more advanced MCU, USB and Ethernet connectivity and two external onboard FLASH memories cost about 175 USD but this price I also consider expensive. In opposition availability is good. Both mentioned boards (EK-RA2L1 and more advanced EK-RA6M4) are available at almost all distributors at the time of writing this review. Also note that there are some ways how to receive boards for free. First possibility is using sample program. While most vendors do not include evaluation boards in sample program, Renesas for some reason included them. Note that even Renesas do not include all evaluation boards in sample program but for some reason EK-RA kits currently are available in sample program. Second possibility to receive EK-RA kit for free is by accessing their (very interesting) webinar. I registered at Renesas website and received link to hand-on lab (webinar) very soon. EK-RA4M3 was offered for free for attendees. I tried applying to this but received email reply (from human from Renesas; not an automatic reply) that kits are not available to students at this time, but if you are attending on behalf of company you probably would be able to receive one kit for free.
EK-RA2L1 is good development board. There are some small bugs in pin labels but technically board is designed well, enables evaluation of MCU and can significantly save time at prototyping time. As a biggest con I classify high price.
This was all from this article. In next article I will review evaluated Microcontroller in detail.