Analogue Pocket MPU Template

The current Specs of the MPU

Specs:

• Running at 74.2mhz (Same as the APF bus)
• Connected to the core via a 16bit HPS Bus
• Two timers - one for interrupts and the other for user timing.
• Currently, 32K of memory/ram for the MPU's program (Will be set to 16K for a smaller footprint)
• A 8Kbyte swap buffer for both the APF and MPU to do transfers - can do up to 32K with changing the bram size. Anything larger would require some
• The address of the swap memory starts at 0x0000_8000 on the MPU side and on the APF address it is at 0x8000_0000 (This can be changed on the .top_address parameter in the verilog code to any address you want on the APF bus)
• Boot Vector is at 0x0000_0000 and the interrupt is at 0x0000_0020 - the startup.S already has the code there for initialation of the MPU with the interrupts turned on.

How to setup

C Compiler for RISCV

• For this you will need the GCC compiler on your computer
• The best resource for setting this up is documented in there under "Build the RISC-V GCC" - https://github.com/SpinalHDL/VexRiscv
• Once there you can look under the \src\VexRiscv location for the main files that are used.
• Main.cpp contains the main loop and initialation of the MPU once the reset line from the APF has assurted the reset_l signal
• apf.cpp/h contains some APF fuctions to request or send data to the buffer area
• timer.cpp/h contains both the interrupt timer and a user timer function
• spi.cpp/h contains the HPS bus interface fuctions that where used to interface the mister framework
• printf.cpp/h the printf function is used with the Analogue debug cart's USB uart port to display debugging commands. The core has a 1024 sized fifo to make sure the CPU is not waiting for sending requests.
• interrupts.cpp/h this will currently turn on and off the timing interrupt mask in the core.
• core.cpp/h this is where the main core could should be for polling data and reseting the core.

The core itself

• The core will automativly start once and run the mpu.bin file when uploaded

Addresses:

• MPU Address 0x00000000 - 0x00008000 / APF Address 0x80000000 - 0x80008000 - Program Ram - locked from the APF bus when running
• MPU Address 0x00008000 - 0x80010000 / APF Address 0x80008000 - 0x80010000 - 8K Buffer mirrored
• MPU Address 0xFFFFFF20 - 0xFFFFFF4c - These are for the reading the joystick inputs from the APF Framework APF Target Dataslot commands
• MPU Address 0xFFFFFF80 - target_dataslot_id
• MPU Address 0xFFFFFF84 - target_dataslot_bridgeaddr
• MPU Address 0xFFFFFF88 - target_dataslot_length
• MPU Address 0xFFFFFF8C - target_dataslot_slotoffset
• MPU Address 0xFFFFFF90 - {target_dataslot_ack, target_dataslot_done, target_dataslot_err[2:0]}

UART Timing

• MPU Address 0xFFFFFF94 - uart_divisor = This is calculated in the UART.c program with the formula ((sys_clock * 1000)/uart_rate)
• MPU Address 0xFFFFFF94 - sysclk_frequency = This is to advise the UART and timers what the CPU clock rate is in MHZ

Timers

• MPU Address 0xFFFFFFC4 - millisecond_counter_1 - This will show the interupt counter in Milliseconds
• MPU Address 0xFFFFFFC8 - interupt_counter_1 - This will set the interrupt timer to interrupt the CPU when both the interrupt mask is on and the counter is greater or equal to this number
• MPU Address 0xFFFFFFCC - millisecond_counter_2 - This will show the interupt counter in Milliseconds

HPS Bus control

• MPU Address 0xFFFFFFD0 - {io_ss2, io_ss1,io_ss0,io_clk,1'b0,IO_DOUT[15:0]}
• MPU Address 0xFFFFFFD0 - {io_ack, IO_WIDE, IO_DIN}

Interrupt Mask

• MPU Address 0xFFFFFFF4 - {interupt_output_1, interupt_output_1_reg, timerenabled}

Why do things take some time to load or save?

• I have recently learnt that the APF does time based checks on requests from the MPU/Target dataslots. So make sure you can do some caching or make the buffer size larger to lower timing for the transfers.
• Try and keep the transfer sizes below 32Kbytes as the APF can change how much it sends if larger then this size

When will writes from the core to the APF bus

Right now the APF file system will re-write data to the file but will resize it to that last data packet you have sent. A bug fix will be coming soon

To Be Done:

• Right now getting malloc and calls working so the swap memory can be cleared when needed
• Write access when the next release canadate is out

Credits

• Analogue for the Pocket and giving me a lot of support on this.
• MiSTer, Mist, DeMiSTify projects and the Communities :-) Love you all
• Mist and their Community.
• VexRISCV Team - https://github.com/SpinalHDL/VexRiscv
• Robinsonb5 for his time answering my questions on his 832 CPU - Tho I did not use this excellent-looking CPU, I was not able to get the C Compiler working 100% on my builds
• Boogerman for some coding questions - You still owe me on the use of my JTAG tho LOL
• Electron Ash, AGG23 as a beta testers.
• And many more, so please message me and I would happily add them to this!!