initial versioin

code/os/04-multitask/platform.h

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+#ifndef __PLATFORM_H__
+#define __PLATFORM_H__
+
+/*
+ * QEMU RISC-V Virt machine with 16550a UART and VirtIO MMIO
+ */
+
+/* 
+ * maximum number of CPUs
+ * see https://github.com/qemu/qemu/blob/master/include/hw/riscv/virt.h
+ * #define VIRT_CPUS_MAX 8
+ */
+#define MAXNUM_CPU 8
+
+/*
+ * MemoryMap
+ * see https://github.com/qemu/qemu/blob/master/hw/riscv/virt.c, virt_memmap[] 
+ * 0x00001000 -- boot ROM, provided by qemu
+ * 0x02000000 -- CLINT
+ * 0x0C000000 -- PLIC
+ * 0x10000000 -- UART0
+ * 0x10001000 -- virtio disk
+ * 0x80000000 -- boot ROM jumps here in machine mode, where we load our kernel
+ */
+
+/* This machine puts UART registers here in physical memory. */
+#define UART0 0x10000000L
+
+#endif /* __PLATFORM_H__ */