I am using the FMC peripheral of the STM32MP157 to access the FPGA, the FMC is configured as a Synchronous read synchronous write PSRAM. For the simplicity of the FPGA logic design I would like to have the burst reads and burst writes with CRAM page size (CPSIZE) fixed at 1024 bits.
This is the device tree configuration:
&fmc {
pinctrl-names = "default", "sleep";
pinctrl-0 = <&fmc_pins_mx>;
pinctrl-1 = <&fmc_sleep_pins_mx>;
status = "okay";
psram@0,0 {
compatible = "mtd-ram";
reg = <0 0x00000000 0x100000>;
bank-width = <2>;
st,fmc2-ebi-cs-transaction-type = <8>;
st,fmc2-ebi-cs-cclk-enable = <1>;
st,fmc2-ebi-cs-mux-enable;
st,fmc2-ebi-cs-buswidth = <16>;
st,fmc2-ebi-cs-clk-period-ns = <60>;
st,fmc2-ebi-cs-cpsize = <128>;
st,fmc2-ebi-cs-data-latency-ns = <0>;
st,fmc2-ebi-cs-write-bus-turnaround-ns = <0>;
st,fmc2-ebi-cs-max-low-pulse-ns = <0>;
};
psram@1,0 {
compatible = "mtd-ram";
reg = <1 0x00000000 0x100000>;
bank-width = <2>;
st,fmc2-ebi-cs-transaction-type = <8>;
st,fmc2-ebi-cs-cclk-enable = <1>;
st,fmc2-ebi-cs-mux-enable;
st,fmc2-ebi-cs-buswidth = <16>;
st,fmc2-ebi-cs-clk-period-ns = <60>;
st,fmc2-ebi-cs-cpsize = <128>;
st,fmc2-ebi-cs-data-latency-ns = <0>;
st,fmc2-ebi-cs-write-bus-turnaround-ns = <0>;
st,fmc2-ebi-cs-max-low-pulse-ns = <0>;
};
};
This is the part of user space program for Linux to read and write PSRAM:
if ((fd1 = open("/dev/mtd6", O_SYNC | O_RDWR)) < 0)
errmsg_die("open()");
if (0 != lseek(fd1, 0, SEEK_SET))
errmsg_die("lseek()");
err = write(fd1, data, size);
if (err < 0)
errmsg_die("write()");
But the actual test found two problems, I got stuck for a long time completely do not know how to solve:
- When reading PSRAM, the length of one burst access cannot reach 1024 bits, but only 256 bits.
- A burst write to PSRAM can reach 1024 bits, but there is a small probability that 256 bits will be written at one time, and there will be a delay before the next round of write operation.
I suspect that this is due to some mechanism with Linux kernel or A7 core, but I am not familiar with the underlying layer at all.
I would like to ask how to solve this problem. Thanks!
