feat : enable FPU in UCOS

This change enable the saving and restoring of FPU
registers during context switch.

[ISDK-60](https://iontra.atlassian.net/browse/ISDK-60)

Signed-off-by: Gaurav <[email protected]>

Author: iontra-gaurav

Ports/RISC-V/RV32/GCC/os_cpu_a.S

@@ -23,7 +23,6 @@
 # For       : RISC-V RV32
 # Toolchain : GNU C Compiler
 #********************************************************************************************************
-# Note(s)   : Hardware FP is not supported.
 #********************************************************************************************************
 
 #********************************************************************************************************
@@ -108,7 +107,7 @@ OSStartHighRdy:
     # value stored in t0 is stored into mepc
     csrw   mepc, t0
 
-# Restore x1 to x31 registers
+# Restore x1 to x31 registers (base registers)
     # load word from memory addres [(0 * 4) + sp] into ra register
     lw     ra,   0 * 4(sp)
     lw     t0,   4 * 4(sp)
@@ -176,7 +175,7 @@ OSCtxSw:
 .align 8
 ucos_intr_exception_handler:
     # save regs to current sp
-    addi sp, sp, -4*32
+    addi sp, sp, -4*64
     # store contents of register ra into memory [(0 * 4) + sp]
     sw     ra,   0 * 4(sp)
     sw     t0,   4 * 4(sp)
@@ -207,6 +206,40 @@ ucos_intr_exception_handler:
     sw     t5,  29 * 4(sp)
     sw     t6,  30 * 4(sp)
 
+    #  save f0 to f31 registers (FPU registers)
+    fsw    f0,  32 * 4(sp)
+    fsw    f1,  33 * 4(sp)
+    fsw    f2,  34 * 4(sp)
+    fsw    f3,  35 * 4(sp)
+    fsw    f4,  36 * 4(sp)
+    fsw    f5,  37 * 4(sp)
+    fsw    f6,  38 * 4(sp)
+    fsw    f7,  39 * 4(sp)
+    fsw    f8,  40 * 4(sp)
+    fsw    f9,  41 * 4(sp)
+    fsw    f10, 42 * 4(sp)
+    fsw    f11, 43 * 4(sp)
+    fsw    f12, 44 * 4(sp)
+    fsw    f13, 45 * 4(sp)
+    fsw    f14, 46 * 4(sp)
+    fsw    f15, 47 * 4(sp)
+    fsw    f16, 48 * 4(sp)
+    fsw    f17, 49 * 4(sp)
+    fsw    f18, 50 * 4(sp)
+    fsw    f19, 51 * 4(sp)
+    fsw    f20, 52 * 4(sp)
+    fsw    f21, 53 * 4(sp)
+    fsw    f22, 54 * 4(sp)
+    fsw    f23, 55 * 4(sp)
+    fsw    f24, 56 * 4(sp)
+    fsw    f25, 57 * 4(sp)
+    fsw    f26, 58 * 4(sp)
+    fsw    f27, 59 * 4(sp)
+    fsw    f28, 60 * 4(sp)
+    fsw    f29, 61 * 4(sp)
+    fsw    f30, 62 * 4(sp)
+    fsw    f31, 63 * 4(sp)
+
     # If it is a ecall, do not add 4 in mepc
     # otherwise add 4 in mepc
     li t1, ARCH_CPU_MCAUSE_CAUSE_MASK
@@ -321,8 +354,42 @@ Software_IRQHandler:
     lw     t5,  29 * 4(sp)
     lw     t6,  30 * 4(sp)
 
+    #  Restore f0 to f31 registers (FPU registers)
+    flw    f0,  32 * 4(sp)
+    flw    f1,  33 * 4(sp)
+    flw    f2,  34 * 4(sp)
+    flw    f3,  35 * 4(sp)
+    flw    f4,  36 * 4(sp)
+    flw    f5,  37 * 4(sp)
+    flw    f6,  38 * 4(sp)
+    flw    f7,  39 * 4(sp)
+    flw    f8,  40 * 4(sp)
+    flw    f9,  41 * 4(sp)
+    flw    f10, 42 * 4(sp)
+    flw    f11, 43 * 4(sp)
+    flw    f12, 44 * 4(sp)
+    flw    f13, 45 * 4(sp)
+    flw    f14, 46 * 4(sp)
+    flw    f15, 47 * 4(sp)
+    flw    f16, 48 * 4(sp)
+    flw    f17, 49 * 4(sp)
+    flw    f18, 50 * 4(sp)
+    flw    f19, 51 * 4(sp)
+    flw    f20, 52 * 4(sp)
+    flw    f21, 53 * 4(sp)
+    flw    f22, 54 * 4(sp)
+    flw    f23, 55 * 4(sp)
+    flw    f24, 56 * 4(sp)
+    flw    f25, 57 * 4(sp)
+    flw    f26, 58 * 4(sp)
+    flw    f27, 59 * 4(sp)
+    flw    f28, 60 * 4(sp)
+    flw    f29, 61 * 4(sp)
+    flw    f30, 62 * 4(sp)
+    flw    f31, 63 * 4(sp)
+
 # Compensate for the stack pointer
-    addi   sp, sp, 4 * 32
+    addi   sp, sp, 4 * 64
 
 # Exception return will restore remaining context
     # set MPIE = 1