Renesas RX65 Envision Kit - part 10: Reserve LCD Frame Buffer in Expansion RAM with GCC

RE: Renesas RX65 Envision Kit - part 10: Reserve LCD Frame Buffer in Expansion RAM with GCC

Jan Cumps — Tue, 21 Jan 2020 11:18:40 GMT

Here's how Trinamic approach fixing something in a known location. Their firmware and boot loader both expect that a structure is at a specific memory location.

It's interesting to see this used in the real world.

https://github.com/trinamic/TMC-EvalSystem/blob/master/main.c

https://github.com/trinamic/TMC-EvalSystem/blob/master/hal/Landungsbruecke/freescale/MK20DN512-TMCM.ld

In the code, they use GCC specific construct to place it in a known memory section:

[embed:dc8ab71f-3b98-42d9-b0f6-e21e02a0f8e2:3ef06e6b-9b7d-4651-b12d-db8be7f5e991:type=c_cpp&text=struct+BootloaderConfig+%7B%0Auint32_t+BLMagic%3B%0Auint32_t+drvEnableResetValue%3B%0A%7D%3B%0A%0A%2F%2F+This+struct+gets+placed+at+a+specific+address+by+the+linker%0Astruct+BootloaderConfig+__attribute__+%28%28section%28%22.bldata%22%29%29%29+BLConfig%3B]

In the linker file, this section is placed at a known location: the begin of RAM:

[embed:dc8ab71f-3b98-42d9-b0f6-e21e02a0f8e2:3ef06e6b-9b7d-4651-b12d-db8be7f5e991:type=text&text=%2F*+Specify+the+memory+areas+*%2F%0AMEMORY%0A%7B%0A++m_interrupts+%28rx%29+%3A+ORIGIN+%3D+0x00008000%2C+LENGTH+%3D+0x1BC%0A++m_cfmprotrom+%28rx%29+%3A+ORIGIN+%3D+0x00008400%2C+LENGTH+%3D+0x10%0A++m_text+%28rx%29+%3A+ORIGIN+%3D+0x00008410%2C+LENGTH+%3D+512K-32K-0x410%0A++m_data++++%28rwx%29+%3A+ORIGIN+%3D+0x1FFF0000%2C+LENGTH+%3D+128K+%2F*+SRAM+*%2F%0A%7D%0A%2F%2F+...%0A++%2F*+special+area+for+data+exchange+between+boot+loader+and+application%0A+++++at+the+beginning+of+the+RAM*%2F%0A++.bldata+%28NOLOAD%29+%3A%0A++%7B%0A++++.+%3D+ALIGN%284%29%3B%0A++++KEEP%28*%28.bldata%29%29%0A++++.+%3D+ALIGN%284%29%3B%0A++%7D+%3E+m_data]

RE: Renesas RX65 Envision Kit - part 10: Reserve LCD Frame Buffer in Expansion RAM with GCC

Jan Cumps — Fri, 20 Dec 2019 16:08:29 GMT

The defect that I logged with Renesas for the wrong memory section in the GCC linker file is not going in the right direction: https://renesasrulz.com/rx/f/rx---forum/15513/ram2-section-in-gcc-linker-script-starts-at-0x80000

I raised that the project generator creates a linker file with incorrect RAM addresses and they ask me if I fixed it meanwhile [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-d3df36d4-a30c-4249-8b8e-d960b01784f2/3681.contentimage_5F00_1.png:16:16]...

RE: Renesas RX65 Envision Kit - part 10: Reserve LCD Frame Buffer in Expansion RAM with GCC

Jan Cumps — Thu, 12 Dec 2019 19:36:40 GMT

What I didn't tell:

If you're just interested in getting a variable or buffer into the expansion RAM, it would suffice to just create a section n the linker file, then use:

[embed:dc8ab71f-3b98-42d9-b0f6-e21e02a0f8e2:3ef06e6b-9b7d-4651-b12d-db8be7f5e991:type=c_cpp&text=uuint32+__attribute__%28%28section+%28%22.FRAME_BUFFER%22%29%29%29+frameBuffer%5Bsize%5D%3B]

The thing with a big buffer like the LCD driver's frame buffer - especially in a microcontroller where there aren't many big chunks of memory available - is that it's hard to get 232000 bytes available in a continuous block available if you don't manage it.

That's why in this case putting it in a known available block makes sense. The linker can have fun allocating room for te small variables. That's not hard, even in a broken memory chunk.

What I didn't tell part 2:

I would not use my method to reserve the memory addresses for registers and memory mapped devices.

In that case, I'd just not make those memory chunks available in the loader script, and use header files - like the majority of HAL layers and microcontroller frameworks do for this type of memory areas.

(

also the Renesas tool chains do that. The red areas below are made unavailable to the linker, and the header files generate all the register addresses and structures:

[View:/resized-image/__size/338x180/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-d3df36d4-a30c-4249-8b8e-d960b01784f2/contentimage_5F00_205579.png:338:180]

)

RE: Renesas RX65 Envision Kit - part 10: Reserve LCD Frame Buffer in Expansion RAM with GCC

Andrew J — Thu, 12 Dec 2019 14:55:18 GMT

Interesting. I don't get why the 2nd block would overrun into the reserved area at 0x00108000. Wouldn't it overrun into the area after 0x00860000?